Chapter 6 Objectives 1/16/16, 12:34 PMChapter 6 Objectives Due: 11:59pm on Friday, January 22, 2016 You will receive no credit for items you complete after the assignment is due. Grading Policy A message from your instructor... Sections 6.1-6.3 Introduction to Thermodynamics Exercise 6.5 Part A What is the SI unit of energy? ANSWER: calorie kilowatt-hour bar joule Correct Part B List some other common units of energy. Check all that apply. ANSWER: lumen newton tesla watt kilowatt-hour calorie Correct ± Exercise 6.34 with feedback You may want to reference ( pages 248 - 250) section 6.2 while completing this problem. Perform each conversion between energy units. Part A cal kJ https://session.masteringchemistry.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 1 of 32 Chapter 6 Objectives 1/16/16, 12:34 PM 215 cal to kJ Express the value in kilojoules to three significant figures. ANSWER: 0.900 kJ Correct To conduct the conversion from calories to kilojoules you needed to first convert the value from calories to joules (4.184 J/1 cal ) and then from joules to kilojoules (1 kJ/1000 J). Part B 2.35×106 kJ to kcal Express the value in kilocalories to three significant figures. ANSWER: 5.62×105 kcal Correct To conduct the conversion from kilojoules to kilocalories you needed to first convert the value from kilojoules to joules (1000 J/1 kJ), then convert from joules to calories ( 1 cal/4.184 J), and finally convert from kilocalories to calories (1 kcal/1000 cal ). Part C 4.68×103 kJ to kW ⋅ h Express the value in kilowatt-hours to three significant figures. ANSWER: 1.30 kW ⋅ h Correct To conduct the conversion from kilojoules to kilowatt-hours you needed to first convert the value from kilojoules to joules (1000 J/1 kJ ) and then from joules to kilowatt-hours (1 kW ⋅ h/3.60 × 106 J). Part D 4.96×104 J to Cal Express the value in Calories to three significant figures. ANSWER: 11.9 Cal https://session.masteringchemistry.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 2 of 32 Chapter 6 Objectives 1/16/16, 12:34 PM Correct To conduct the conversion from joules to calories you needed to convert the value using the conversion factor 1 Cal/4184 J ). Conversions are useful when doing calculations. Being able to do correctly make correlations is a useful skill for future studies. ±Exercise 6.36 with feedback A particular frost-free refrigerator uses about 705 kWh of electrical energy per year. You may want to reference ( pages 248 - 250) Section 6.2 while completing this problem. Part A Express this amount of energy in joules (J ). ANSWER: 2.54×109 J Correct The energy in joules is equal to the energy in kilowatt-hours multiplied by 3.6 × 106 . Part B Express this amount of energy in kilojoules (kJ). ANSWER: 2.54×106 kJ Correct The energy in kilojoules is equal to the energy in joules divided by 1000. Part C Express this amount of energy in Calories (Cal). ANSWER: 6.07×105 Cal Correct The energy in Cal is equal to the energy in J divided by 4184. Conceptual Connection 6.2 https://session.masteringchemistry.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 3 of 32 com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 4 of 32 . Drag the appropriate items to their respective bins.Chapter 6 Objectives 1/16/16. ANSWER: https://session. 12:34 PM Part A Identify each energy exchange as heat or work and determine whether the sign of heat or work (relative to the system) is positive or negative.masteringchemistry. ANSWER: Part B Drag the appropriate items to their respective bins. Chapter 6 Objectives 1/16/16.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 5 of 32 .1 Consider these fictitious internal energy gauges for a chemical system and its surroundings: Part A Which diagram best represents the energy gauges for the same system and surroundings following an energy exchange in which ∆Esys is negative? ANSWER: https://session.masteringchemistry. 12:34 PM Conceptual Connection 6. (The evaporating sweat is the system. An aqueous chemical reaction mixture is warmed with an external flame.) Part A Identify energy exchanges as primarily heat or work. A balloon expands against an external pressure. cooling the skin. a. 12:34 PM Exercise 6.) c. Drag the items into the appropriate bins.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 6 of 32 .) b.Chapter 6 Objectives 1/16/16. (The contents of the balloon is the system. ANSWER: Part B Determine whether the sign of ∆E is positive or negative for the system. Drag the items into the appropriate bins. Sweat evaporates from skin. (The reaction mixture is the system.masteringchemistry.39 Identify each of the following energy exchanges as primarily heat or work and determine whether the sign of ∆E is positive or negative for the system. ANSWER: https://session. 44 https://session. Part A What is the change in internal energy of the system? Express the internal energy in kilojoules to three significant figures.41 A system releases 691 kJ of heat and does 140 kJ of work on the surroundings.256) section 6. Part A What is the change in internal energy of the system? ANSWER: ∆E = kJ Exercise 6.42 with feedback You may want to reference ( pages 250 .com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 7 of 32 .Chapter 6 Objectives 1/16/16. A system absorbs 195 kJ of heat and the surroundings do 110 kJ of work on the system. 12:34 PM Exercise 6. ANSWER: ∆E = kJ Exercise 6.masteringchemistry.3 while completing this problem. or q = mC s ∆T . Sections 6.0 g piece of unknown metal from 13. ANSWER: ∆E = kJ A message from your instructor. it does 75 kJ of work. ANSWER: Cs = Parts B and C The next two questions pertain to silver. The units for specific heat are J/(g ⋅ ∘ C) .0 g of silver by 18.. A second method is to report how much energy it takes to raise the temperature of one gram of a substance by exactly 1 degree Celsius. we know that it takes much more energy to heat a large tank of water than a small cup.8 ∘ C? Express your answer with the appropriate units. specific heat.4 ∘ C . Part A What is the change in internal energy for the system? Express your answer using two significant figures. where m denotes the number of grams of the substance. For example. As it expands. q = nC p∆T ..0∘ C to 24. where n denotes the number of moles of the substance. Part A It takes 55.The molar heat capacity is given in the units J/(mol ⋅ ∘C) . which has the symbol Cp . C . How much energy would it take to raise the temperature of 11. The energy needed to warm an object increases as the mass of that object increases. 12:34 PM The air in an inflated balloon (defined as the system) is warmed over a toaster and absorbs 130 J of heat.0 J to raise the temperature of an 11. We see this in our everyday life.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 8 of 32 .Chapter 6 Objectives 1/16/16. You did not open hints for this part. Heat capacity. This value is the molar heat capacity.4-6.35 J/mol ⋅ ∘C . What is the specific heat for the metal? Express your answer with the appropriate units. That is. Because of this dependence on mass. One method is to report how much energy it takes to raise the temperature of one mole of a substance by exactly 1 degree Celsius. Part B The molar heat capacity of silver is 25. https://session.masteringchemistry.5 Calorimetry Heat Capacity Learning Goal: To understand the concepts of heat capacity. experimentally determined heat capacities are always reported in terms of the amount of the substance that is heated. which has been given the symbol C s . is the amount of energy required to raise the temperature of a substance by exactly 1 degree Celsius. and molar heat capacity. They have nothing to do with unknown metal described in Part A. The heat capacity of a substance is therefore related to the energy q needed to raise its temperature by an amount ∆T . This value is the specific heat. You fill your bathtub with 25 kg of room-temperature water (about 25 ∘ C ). ANSWER: q= Part C What is the specific heat of silver? Express your answer with the appropriate units.Chapter 6 Objectives 1/16/16. In a system in which two objects of different temperatures come into contact with one another. but you want to take a bath. J/(mol ⋅ ∘C) J/(g ⋅ ∘C) https://session. 12:34 PM You did not open hints for this part. the warmer object will cool and the cooler object will warm up until the system is at a single equilibrium temperature. You did not open hints for this part. You figure that you can boil water on the stove and pour it into the bath to raise the temperature. Part A How much boiling water would you need to raise the bath to body temperature (about 37 ∘ C )? Assume that no heat is transferred to the surrounding environment.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 9 of 32 . ANSWER: Part B This question will be shown after you complete previous question(s). Specific Heat The heat capacity of an object indicates how much energy that object can absorb for a given increase in that object's temperature. You did not open hints for this part. Express your answer to two significant figures and include the appropriate units. ANSWER: Using the Law of Conservation of Energy Imagine that your water heater has broken.masteringchemistry. When you click the simulation link. which has units of J/(mol ⋅ ∘C) . If the final ∘C temperature of the system is 21.00 C is placed in the water.Energy Forms and Changes Energy can exist in a variety of forms. energy going into system) or exothermic (exo-. Express your answer to three significant figures and include the appropriate units.18 J/(g ⋅ C) ∘ specific heat of steel = 0. respectively. Choose to run or open it. Part A ∘ ∘ A volume of 110.masteringchemistry. Click on the image below to explore this simulation. 12:34 PM Note the difference between the terms molar heat capacity.Chapter 6 Objectives 1/16/16. The true number of significant digits may be more or less. mL of H2 O is initially at room temperature (22.00 C). Energy is never lost. what is the mass of the steel bar? Use the following values: ∘ specific heat of water = 4. Calculate the molar heat capacity of water. which shows the how energy is transferred between objects in either the same form or through conversions. which has units of J/(g ⋅ ∘ C) . In this problem answers are requested to three significant digits for grading purposes. energy leaving system). and specific heat. When examining a system. A chilled steel rod at 2. and w signifies the work done on a system. The processes of energy transfer can be described as endothermic (endo-.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 10 of 32 . The values for q and w can be negative if the system loses heat or performs work. ANSWER: mass of the steel = Part B The specific heat of water is 4. the internal energy of that system can change such that it loses/gains energy to/from its surroundings. open. and the form of energy does not matter. https://session. you may be asked whether to run. but rather it is converted between forms.452 J/(g ⋅ C) Express your answer to three significant figures and include the appropriate units. You did not open hints for this part. The change in the internal energy of a system is: ∆E = Efinal − Einitial which can also be simply represented by: E = q + w where q signifies the heat absorbed (or released) by the system. or save the file.00 .18 J/(g ⋅ ∘ C). ANSWER: molar heat capacity for water = PhET Simulation . You did not open hints for this part. Perform the described tasks and fill in the blanks with the appropriate terms. click on the Intro tab and check the “Energy Symbols” box in the upper right.masteringchemistry. Match the words in the left column to the appropriate blanks in the sentences on the right. Checking the “Energy Symbols” box in the upper right allows you to view the internal energy of the objects and the transfer of thermal energy. 12:34 PM When the simulation is opened. ANSWER: https://session. Clicking the Energy Systems tab of the simulation allows you to view energy conversions by connecting different energy producing and energy converting sources.Chapter 6 Objectives 1/16/16. Make certain each sentence is complete before submitting your answer. You did not open hints for this part. Part A In the PhET simulation window.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 11 of 32 . There are twelve different working configurations for these sources. you will see various objects that can be placed on a heating/cooling surface. Observe the forms of energy as they are converted and correctly identify the energy conversions for each. the sign on the value for qsys would be . Drag the beaker of water onto the support. but rather it is converted between forms. and the ice is considered part of the . ANSWER: https://session. and use the simulation to recreate the illustrated energy conversion processes. and it system thermal energy from the fire. and many transformations of energy can occur to drive a process (perform work). 12:34 PM Reset Help surroundings 1. the water thermal energy positive to the ice. exothermic which makes water the being studied. it is never lost. negative 3.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 12 of 32 . click the Energy Systems tab. endothermic 2. You did not open hints for this part.masteringchemistry. Drag the appropriate systems to their respective targets. In this situation. The internal energy of water will be analyzed. When the slider is dragged down to cool the water. When the water is heated. This transfer of heat is an process.Chapter 6 Objectives 1/16/16. Potential energy can be stored in a system before it is converted to kinetic energy. loses 4. check the “Energy Symbols” box in the upper right. Conversion of Energy Even if energy seems to disappear. Part B In the PhET simulation window. and the sign on the value for qsys would gains be . 5. the water undergoes an process. This is the principle described in the first law of thermodynamics. iron (0. overlap them. Heat capacity refers to the temperature changes in the same state of matter.masteringchemistry. Rank from lowest resulting temperature to highest resulting temperature.19 J/g ⋅ ∘C ). ANSWER: https://session. whereas the per unit energies required to melt and boil a substance are called the enthalpies of fusion and vaporization. 12:34 PM Heat capacity Heat capacity refers to how much energy a material can absorb with respect to changes in average kinetic energy.01 J/g ⋅ ∘ C) were held at the same initial temperature and heated for an equivalent amount of time. brick (0. and ∆T is the change in temperature.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 13 of 32 .46 J/g ⋅ ∘ C). Indicate the relative final temperatures by ordering from lowest to highest resulting temperature (if using the Intro tab of the PhET to help visualize the temperature changes. You did not open hints for this part. and the brick has a mass of 0. and plastic are 1 kg in mass. which can sometimes refer the moles of material). Part C Suppose 1 kg each of water (4. and its specific heat capacity quantifies the exact amount of energy it takes to raise 1 g of the material's temperature by 1 ∘ C (depending on the units. assume the water iron. respectively.90 J/g ⋅ ∘C). To rank items as equivalent.Chapter 6 Objectives 1/16/16. and plastic (1. Assume no heat is lost to the surroundings.5 kg ). cs is the specific heat. The relationship between heat and temperature change is described by the following equation: q = mcs ∆T where q is the heat absorbed or lost. m is the mass. what temperature would it reach before losing heat to the surroundings? q = mcs ∆T cs.Chapter 6 Objectives 1/16/16.450 J/g ⋅ ∘C cs.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 14 of 32 . Fe(s) = 0. What temperature would the block of iron reach assuming the complete transfer of heat and no loss to the surroundings? If the same amount of heat was quickly transferred to a 840 g pellet of copper at 30 ∘ C . come in contact with each other and reach thermal equilibrium. Cu(s) = 0. The mass of substance A is twice the mass of substance B. 12:34 PM Part D A 1. Cu = ∘C Conceptual Connection 6.7 kg block of iron at 35 ∘ C is rapidly heated by a torch such that 13 kJ is transferred to it.385 J/g ⋅ ∘C Express the final temperatures of the iron and copper in ∘ C to two significant figures separated by a comma. Part A Which statement is true about the final temperature of the two substances once thermal equilibrium is reached? ANSWER: https://session. ANSWER: Final temperatures of Fe .4 Substances A and B.masteringchemistry. You did not open hints for this part. initially at different temperatures. The specific heat capacity of substance B is twice the specific heat capacity of substance A. 262) section 6. An unknown mass of each of the following substances.0 ∘ C ) Express your answer using two significant figures.0 ∘ C to 46.18J/g∘ C . Find the mass of each substance. ANSWER: https://session.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 15 of 32 .0 ∘ C.5 ∘ C) Express your answer using two significant figures.4 while completing this problem. Pyrex glass (T f = 55. Cs = 4. ANSWER: m= g Part B sand (Tf = 62. The final temperature will be exactly midway between the initial temperatures of substances A and B.50 with feedback You may want to reference ( pages 258 .5 ∘ C) Express your answer using two significant figures. Self Assessment 6. The final temperature is recorded as indicated.Chapter 6 Objectives 1/16/16. 12:34 PM The final temperature will be closer to the initial temperature of substance A than substance B. Part A a. absorbs 1960 J of heat.3 Part A How much heat must be absorbed by a 16. ANSWER: ± Exercise 6.masteringchemistry.0 ∘ C ? (For water.0 g sample of water to raise its temperature from 30. initially at 21. ANSWER: m= g Part C ethanol (T f = 44. The final temperature will be closer to the initial temperature of substance B than substance A.) Express your answer to three significant figures and include the appropriate units. ANSWER: m= g ± Exercise 6..72 kJ/ C .552 g of liquid hexane (C6 H14 ) undergoes combustion in a bomb calorimeter. initially at 10. 12:34 PM m= g Part D water (Tf = 32.masteringchemistry.Chapter 6 Objectives 1/16/16. is 5..262) section 6.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 16 of 32 . Find ∘ ∆Erxn for the reaction in kJ/mol hexane.83 ∘ C .5 Part A When 1.6 Stoichiometry of Enthalpy Self Assessment 6.6 Part A (C8H18) ∘C https://session. You may want to reference ( pages 256 . Express your answer using three significant figures.4 while completing this problem. determined in a separate experiment. Section 6.92 g of water at 52.8 C in an insulated container. Part A What is the final temperature of both the weight and the water at thermal equilibrium? Express the temperature in Celsius to three significant figures.68 with feedback ∘ ∘ A 2. ANSWER: T = ∘C For Practice 6. is submerged in 7.02 g lead weight. The heat capacity of the bomb calorimeter.72 ∘ C to 38. the temperature rises from 25.4 ∘ C ) Express your answer using two significant figures. ANSWER: ∆Erxn = kJ/mol A message from your instructor.6 C . The heat ∘ capacity of the calorimeter. ANSWER: ∆Erxn = kJ/mol For Practice 6.masteringchemistry. 12:34 PM When a 4.6 ∘ C . is 6. Express your answer using three significant figures.23 kJ/ C . Drag the appropriate items to their respective bins. measured in a separate experiment.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 17 of 32 .Chapter 6 Objectives 1/16/16. ANSWER: Part B An endothermic reaction has a ANSWER: positive ∆H negative ∆H positive or negative ∆H https://session.50 g sample of liquid octane (C 8H18) is burned in a bomb calorimeter. the temperature of the calorimeter rises by 27. Determine ∆Erxn for the combustion of octane in units of kJ/mol octane.6 Part A Identify each process as endothermic or exothermic and indicate the sign of ∆H . 63 (C3 H8 ) https://session.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 18 of 32 . ANSWER: m(Ti) = Part B Express your answer to three significant figures and include the appropriate units. Express your answer to three significant figures and include the appropriate units.61 Nitromethane (CH3 NO2 ) burns in air to produce significant amounts of heat. 2CH3 NO2 (l) + 3/2O2 (g)→2CO2 (g) + 3H2O(l) + N2(g) o ∆Hrxn = -1418 kJ Part A How much heat is produced by the complete reaction of 4.masteringchemistry.26 kg of nitromethane? Express your answer to three significant figures and include the appropriate units.66×103 kJ of heat is emitted by the reaction.Chapter 6 Objectives 1/16/16. 12:34 PM Part C An exothermic reaction has a ANSWER: positive ∆H negative ∆H positive or negative ∆H Exercise 6.62 Titanium reacts with iodine to form titanium(III) iodide. ANSWER: Exercise 6. emitting heat. ANSWER: m(I2 ) = Exercise 6. 2Ti(s) + 3I2(g)→2TiI3 (s)∆Hrxn o = -839 kJ Part A Determine the masses of titanium and iodine that react if 1. A simple constant-pressure calorimeter can be made from a foam coffee cup and a thermometer. any energy gained or lost in the chemical reaction will be directly observable as a temperature and/or pressure change in the calorimeter. 12:34 PM The propane fuel (C3 H8 ) used in gas barbeques burns according to the following thermochemical equation: C3H8 (g) + 5O2 (g) → 3CO2 (g) + 4H2 O(g) ∘ ∆ Hrxn = −2217kJ Part A If a pork roast must absorb 1600 kJ to fully cook.7 Calorimetry and Enthalpy of Reaction Coffee Cup Calorimetry Calorimetry is a method used to measure enthalpy. Two common calorimeters are constant- pressure calorimeters and constant-volume (or "bomb") calorimeters.12 Part A Which process is endothermic? ANSWER: The melting of ice.00 to 24. ANSWER: m= g Self Assessment 6. Part A A total of 2. What is the enthalpy of this reaction? Assume that no heat is lost to the surroundings or to the coffee cup itself and that the specific heat of the solution is the same as that of pure water.70 ∘ C . what mass of CO2 is emitted into the atmosphere during the grilling of the pork roast? Express your answer using two significant figures. https://session.. Enter your answer in kilojoules per mole of compound to three significant figures.masteringchemistry. Section 6.. The idea behind calorimeters is that if they are sufficiently insulated from the outside environment. You did not open hints for this part. where the reaction is observed in a strong. The reaction caused the temperature of the solution to rise from 21. Bomb calorimeters are used to measure combustion and other gas-producing reactions. or heat. The combustion of natural gas in a stove.00 mol of a compound is allowed to react with water in a foam coffee cup and the reaction produces 178 g of solution.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 19 of 32 . changes that occur during chemical processes.Chapter 6 Objectives 1/16/16. The burning of sugar. and if only 14% of the heat produced by the barbeque is actually absorbed by the roast. A message from your instructor. sealed vessel. energy changes in a reaction are observed via a temperature change of the solution in the cup. The oxidation of iron in a chemical hand warmer. Express the change in internal energy in kilojoules per mole to three significant figures. ∆H = qp but it is usually expressed per mole of reactant and with a sign opposite to that of q for the surroundings. it dissolves via the reaction X(s) + H2 O(l)→X(aq) and the temperature of the solution increases to 28. the equation becomes q = C × ∆T At constant pressure.50 kJ/ C . By measuring the temperature change. ANSWER: https://session. and work done. When 1. ∆E . was burned in a bomb calorimeter with a heat capacity of 7. 12:34 PM ANSWER: ∆H = kJ/mol ± Calorimetry A calorimeter is an insulated device in which a chemical reaction is contained. for this reaction per mole of X . Calculate the enthalpy change.00 g/mL .0 g of sucrose. ∆H . w: ∆E = q + w However. ∆H . and that no heat is lost to the calorimeter itself.18 J/(g ⋅ ∘ C) ]. Part A A calorimeter contains 32. ∆T .0 g/mol ) is added. You did not open hints for this part.20 g of X (a substance with a molar mass of 62. ∆E (sometimes referred to as ∆U ). is the sum of heat. that is. You did not open hints for this part. nor to the surroundings. C . is equal to the heat. if the calorimeter has a predetermined heat capacity. ANSWER: ∆H = kJ/mol Part B Consider the reaction C12H22O11 (s) + 12O 2 (g)→12CO2 (g) + 11H2 O(l) ∘ in which 10. The temperature increase ∘ inside the calorimeter was found to be 22. qp . Express the change in enthalpy in kilojoules per mole to three significant figures. we can calculate the heat released or absorbed during the reaction using the following equation: q = specific heat × mass × ∆T Or. that density of water is 1. the enthalpy change for the reaction.0 C .masteringchemistry. for this reaction per mole of sucrose. Assume that the specific heat of the resulting solution is equal to that of water [4. q . Calculate the change in internal energy. The total internal energy change.0 ∘C . at constant volume (as with a bomb calorimeter) w = 0 and so ∆E = qv .Chapter 6 Objectives 1/16/16. C12H22O 11.0 mL of water at 11.5 ∘ C .com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 20 of 32 . 01 J/(g ⋅ ∘ C) and ∆ Hfus = 6. q .0 ice 2. Express your answer to three significant figures and include the appropriate units.0 kJ/mol at 25. For water.18 J/(g ⋅ ∘ C) for H2 O(l) . ∆Hvap = 44.39×103 kJ ? For ice.0 ∘C . Express your answer to three significant figures and include the appropriate units.Chapter 6 Objectives 1/16/16.7 ∘C if the available heat for this process is 4. n is the number of moles and ∆H is the enthalpy of fusion. ANSWER: ± Heat of Solution https://session. The following table provides the specific heat and enthalpy changes for water and ice. or sublimation.7 ∘ C can be completely converted to liquid at 11. Heat can also be transferred at a constant temperature when there is a change in state.01 6. use a specific heat of 2. For a process that involves a phase change q = n ⋅ ∆H where.01 Part A Calculate the enthalpy change.01kJ/mol . vaporization.0 ∘ C and Cs = 4.3 g of water is converted from liquid at 17. Specific heat ∆H Substance [J/(g ⋅ ∘ C)] (kJ/mol) water 4.18 44. 12:34 PM ∆E = kJ/mol ± Enthalpy of a Phase Change Heat. for the process in which 29. You did not open hints for this part. ∆H . You did not open hints for this part. is energy transferred between a system and its surroundings.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 21 of 32 .masteringchemistry. ANSWER: ∆H = Part B How many grams of ice at -12. For a process that involves a temperature change q = m ⋅ Cs ⋅ ∆T where Cs is specific heat and m is mass.9 ∘C to vapor at 25. Hess's law states that ∆H for an overall reaction is the sum of the ∆H values for the individual reactions.masteringchemistry. Part A Find ∆ Hrxn for this reaction as written. ANSWER: Exercise 6. Express your answer with the appropriate units. If 4.8 kJ/mol ..75 Zinc metal reacts with hydrochloric acid according to the following balanced equation.0 ∘ C . a coffee-cup calorimeter containing 100 mL of H2 O is used. A simple constant-pressure calorimeter can be made from a foam coffee cup and a thermometer.Chapter 6 Objectives 1/16/16. if we wanted to know the enthalpy change for the reaction 3Mn + 3O2 →3MnO2 we could calculate it using the enthalpy values for the following individual steps: Step 1: 4Al + 3O2 →2A l2 O3 Step 2: 3Mn + 2Al 2O 3→3Mn O2 + 4Al 3Mn + 3O2 →3MnO2 https://session.0 g/mL for the density of the solution and 4. Part A In the following experiment. Zn(s) + 2HCl(aq)→ZnCl 2(aq) + H2(g) When 0.2 ∘ C .113 g of Zn(s) is combined with enough HCl to make 55. sealed vessel. in which energy changes in a reaction are observed via the change in temperature of the solution in the cup. The idea behind calorimeters is that if they are sufficiently insulated from the outside environment. in which the reaction is observed in a strong. Section 6. what will be the final temperature of the solution in the calorimeter? The heat of solution ∆Hsoln of CaCl 2 is −82.) ANSWER: ∆Hrxn = kJ/mol A message from your instructor. all of the zinc reacts. Bomb calorimeters are used to measure combustion and other gas- producing reactions.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 22 of 32 . Two common calorimeters are constant-pressure calorimeters and constant-volume (or "bomb") calorimeters. raising the temperature of the solution from 21. (Use 1. ∆H . that occur during chemical processes.8 ∘ C to 24.18 J/g ⋅ ∘C as the specific heat capacity. The initial temperature of the calorimeter is 23.8 Hess' Law Procedure for Using Hess's Law Learning Goal: To understand how to use Hess's law to find the enthalpy of an overall reaction.. or heat. The change in enthalpy. 12:34 PM Calorimetry is a method used to measure changes in enthalpy. For example. any energy gained or lost in the chemical reaction will be directly observable as a temperature and/or pressure change in the calorimeter. You did not open hints for this part.0 mL of solution in a coffee-cup calorimeter.60 g of CaCl2 is added to the calorimeter. is the heat absorbed or produced during any reaction at constant pressure. The most easily measurable form of energy comes in the form of heat. In other words. Now consider the following set of reactions: 1 1.masteringchemistry. Which one? You did not open hints for this part. 12:34 PM Overall: 3Mn + 3O2 →3MnO2 If the enthalpy change is −3352 kJ/mol for step 1 and 1792 kJ/mol for step 2. one of them must be reversed. ∆H= −283 2 kJ/mol 2. or enthalpy. The enthalpy of a reaction can be calculated from the heats of formation of the substances involved in the reaction: ∘ = Σ n ∆H ∘ (products) − Σ n ∆H ∘ (reactants) ∆Hrxn p f r f where n represents the stoichiometric coefficients. then the enthalpy change for the overall reaction is calculated as follows: ∆H = −3352 + 1792 = −1560 kJ/mol It is also important to note that the change in enthalpy is a state function.9 Enthalpy's of Formation Chemical Energy Chemical energy is released or absorbed from reactions in various forms. ANSWER: reaction 1 : CO + 12 O2→C O2 reaction 2 : C + O2 →C O2 Part B This question will be shown after you complete previous question(s).. https://session. CO + O2 →CO2 . Part C This question will be shown after you complete previous question(s). C + O2 →CO2 . A message from your instructor. the sum of the ∆H values for any set of reactions that produce the desired product from the starting materials gives the same overall ∆H . ∆H= −393 kJ/mol Part A The equations given in the problem introduction can be added together to give the following reaction: 1 overall: C + 2 O2 →CO However. Section 6. meaning it is independent of path.Chapter 6 Objectives 1/16/16.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 23 of 32 .. ∘ . where the subscript "rxn" stands for "reaction. are an important part of this equation. ANSWER: ∘ = ∆Hrxn Part B This question will be shown after you complete previous question(s). https://session. The standard enthalpy of reaction is the enthalpy change that occurs in a reaction when all the reactants and products are in their standard states. b. the standard enthalpy ∆Hrxn reaction is given by ∆Hrxn ∘ = c∆H ∘ (C) + d∆H ∘ (D) −a∆H ∘ (A) − b∆H ∘ (B) f f f f Notice that the stoichiometric coefficients.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 24 of 32 .Chapter 6 Objectives 1/16/16. Standard Enthalpy of Reaction Learning Goal: To understand how standard enthalpy of reaction is related to the standard heats of formation of the reactants and products. where the first sum on the right-hand side of the equation is a sum over the products and the second sum is over the reactants: ∘ =∑ ∘ ∘ ∆Hrxn products n∆Hf − ∑reactantsm∆Hf where m and n represent the appropriate stoichiometric coefficients for each substance. the standard enthalpy ∘ of any reaction can be mathematically determined. aA + bB→cC + dD. as long as the standard heats of formation (∆H ∘ ) of its reactants and products are ∆Hrxn f known. 12:34 PM Part A Calculate the standard enthalpy change for the reaction 2A + B ⇌ 2C + 2D Use the following data: ∆Hf∘ Substance ( kJ/mol) A -269 B -419 C 181 D -525 Express your answer to three significant figures and include the appropriate units. a . You did not open hints for this part. This formula is often generalized as follows. Therefore. ∘ of the In a generic chemical reaction involving reactants A and B and products C and D. c." The standard enthalpy of a reaction is The symbol for the standard enthalpy of reaction is ∆Hrxn ∘ calculated from the standard heats of formation (∆H f ) (subscript "f" for formation) of its reactants and products.masteringchemistry. Part A ∘ for the following chemical reaction? What is ∆Hrxn H2 O(l) + CCl4 (l)→COCl 2 (g) + 2HCl(g) You can use the following table of standard heats of formation (∆ Hf∘) to calculate the enthalpy of the given reaction. d. the reaction 2NO(g) + O2 (g) ⇌ 2NO2 (g) with heat of formation values given by the following table: ∆Hf∘ Substance (kJ/mol ) NO(g) 90. You did not open hints for this part. Consider. You did not open hints for this part. ∆Hf∘.2) − [2(90. Heat of formation values can be used to calculate the enthalpy change of any reaction.6 Express the standard enthalpy of reaction to three significant figures and include the appropriate units.2 Then the standard heat of reaction for the overall reaction is ∘ = ∆ H ∘(products)− ∆H ∘ (reactants) ∆Hrxn f f = 2(33. 12:34 PM Element/ Standard Heat of Element/ Standard Heat of Compound Formation (kJ/mol) Compound Formation (kJ/mol) H(g) 218 N(g) 473 H2 (g) 0 O2 (g) 0 CCl 4(l) −139. elements in their standard states have ∆Hf∘ = 0 .2) + 0] = −114 kJ Part A ∘ equal to ∆H ∘ of the product(s)? For which of the following reactions is ∆Hrxn f You do not need to look up any values to answer this question. is defined as the enthalpy change for the formation of one mole of substance from its constituent elements in their standard states. for example. ANSWER: Formation Reactions The standard heat of formation.5 O(g) 249 H2 O(l) −285.30kJ C(g) 71 COCl 2 (g) −218.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 25 of 32 .2 O2 (g) 0 NO2 (g) 33. https://session. Check all that apply.masteringchemistry.8 HCl(g) −92.Chapter 6 Objectives 1/16/16.8kJ C(s) 0 HNO3 (aq) −206. Thus. masteringchemistry. occurs via the reaction C3H8 (g) + 5O2 (g)→3CO2 (g) + 4H2 O(g) with heat of formation values given by the following table: ∆Hf∘ Substance ( kJ/mol ) C3H8 (g) -104.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 26 of 32 . The standard conditions are 1 atm pressure.7 CO2 (g) − 393. C3 H8 . A "standard enthalpies of formation table" containing ∆Hf values might look something like this: Substance ∆Hf∘ H(g) 218 kJ/mol H2 (g) 0 kJ/mol Ca(s) 0 kJ/mol Ca2+(aq) − 543 kJ/mol C(g) 71 kJ/mol C(s) 0 kJ/mol N(g) 473 kJ/mol O2 (g) kJ/mol https://session.Chapter 6 Objectives 1/16/16. graphite) + O2 (g)→CO2 (g) CaCO3 (g)→CaO + CO2 (g) CO(g) + 12 O2 (g)→CO2 (g) 2Li(s) + Cl2 (g)→2LiCl(s) Part B The combustion of propane. Express your answer to four significant figures and include the appropriate units. a temperature of 25 ∘ C . ANSWER: ∘ = ∆Hrxn Standard Enthalpy of Formation Reaction ∘ The standard enthalpy of formation (∆ Hf ) is the enthalpy change that occurs when exactly 1 mol of a compound is formed from its constituent elements under standard conditions. and all the species present at a ∘ concentration of 1 M .5 H2 O(g) − 241.8 Calculate the enthalpy for the combustion of 1 mole of propane. 12:34 PM ANSWER: Li(s) + 12 Cl 2 (l)→LiCl(s) Li(s) + 12 Cl 2 (g)→LiCl(s) C(s. You did not open hints for this part. e. The following table lists some enthalpy of formation values for selected substances. Use (aq ) for aqueous solution.6 H2 O(g) −241. 1/3). liquid. Express your answer as a chemical equation.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 27 of 32 . Substance ∆Hf ∘ (kJ/mol) HCl(g) −92. Chemical reactions involve changes in enthalpy. or gas.0 Al(OH) 3(s) −1277.8 AlCl3 (s) −705. You did not open hints for this part.masteringchemistry.8 Part A Determine the enthalpy for this reaction: Al(OH)3 (s) + 3HCl(g)→AlCl 3 (s) + 3H2 O(l) Express your answer in kilojoules per mole to one decimal place. ANSWER: ± Enthalpy Enthalpy H is a measure of the energy content of a system at constant pressure. or (g ) for solid. ANSWER: ∆Hrxn∘ = kJ/mol https://session.Chapter 6 Objectives 1/16/16. ∆H . (l ). You did not open hints for this part. respectively without indicating allotropes. which can be measured and calculated: ∆Hrxn∘ = ∑products m∆Hf ∘ − ∑reactants n∆H f ∘ where the subscript "rxn" is for "enthalpy of reaction" and "f" is for "enthalpy of formation" and m and n represent the appropriate stoichiometric coefficients for each substance. enter them as a fraction (i. Indicate the physical states using the abbreviation (s ).0 H2 O(l) −285. 12:34 PM O2 (g) 0 kJ/mol O(g) 249 kJ/mol S2 (g) 129 kJ/mol Part A ∘ What is the balanced chemical equation for the reaction used to calculate ∆Hf of CaCO3 (s) ? If fractional coefficients are required. 12:34 PM Part B Consider the reaction 2Al(OH)3 (s)→Al2 O3 (s) + 3H2 O(l) with enthalpy of reaction ∆Hrxn∘ = 21. ∘ Substance ∆Hf (kJ/mol) C(g) 718. Imagine a hypothetical process in which the methane molecule.4 CF4 (g) − 679. CH4 .0kJ/mol What is the enthalpy of formation of Al 2O3 (s)? Express your answer in kilojoules per mole to one decimal place. You did not open hints for this part. We then have the process CH4 (g)→C(g) + 4H(g) Part A Compare the reaction for the "expansion" of methane with the reverse of the reaction that represents the standard enthalpy of formation.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 28 of 32 . You did not open hints for this part.masteringchemistry.9 CH4 (g) − 74. is "expanded. Which properties are the same for both reactions and which are different? Drag each item to the appropriate bin.94 HF(g) − 268.61 Keep in mind that the enthalpy of formation of an element in its standard state is zero.Chapter 6 Objectives 1/16/16." by simultaneously extending all four C−H bonds to infinity. ANSWER: ∆Hf ∘ = kJ/mol ± Enthalpy of Reaction: State and Stoichiometry Use the data below to answer the questions.8 H(g) 217. ANSWER: https://session. 440 mol of fluorine.Chapter 6 Objectives 1/16/16. how much heat is released? Express your answer to three significant figures and include the appropriate units. ANSWER: heat = Exercise 6.290 mol of methane.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 29 of 32 .87 https://session. forming CF4 (g) and HF(g) as sole products. Assuming that the reaction occurs at constant pressure. You did not open hints for this part. Part D Suppose that 0.masteringchemistry. Part C This question will be shown after you complete previous question(s). 12:34 PM Part B This question will be shown after you complete previous question(s). F2 (g) . is reacted with 0. C H4(g). Chapter 6 Objectives 1/16/16. What is the correct formation equation corresponding to this ∆Hfo ? ANSWER: https://session. ANSWER: ∘ ∆Hrxn = kJ Part B ∘ Use standard enthalpies of formation to calculate ∆Hrxn for the following reaction. 12:34 PM Part A ∘ Use standard enthalpies of formation to calculate ∆Hrxn for the following reaction.14 Part A The standard enthalpy of formation for calcium phosphate [Ca3 (PO4 )2 (s)] is −4120.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 30 of 32 . Ca(OH) 2(s)→CaO(s) + H2O(g) Express your answer using three significant figures. 2NaHCO3(s)→Na2O(s) + 2CO2(g) + H2 O(g) Express your answer using four significant figures. CO(g) + H2 O(g) → H2 (g) + CO2 (g) Express your answer using three significant figures. ANSWER: ∘ = ∆Hrxn kJ Part C ∘ Use standard enthalpies of formation to calculate ∆Hrxn for the following reaction.8 kJ/mol. Use standard enthalpies of formation to calculate ∆Hrxn Cr2O3 (s) + 3CO(g) → 2Cr(s) + 3CO2 (g) Express your answer using four significant figures. ANSWER: ∘ = ∆Hrxn kJ Self Assessment 6. ANSWER: ∘ = ∆Hrxn kJ Part D ∘ for the following reaction.masteringchemistry. The temperature of the ∘ ∘ calorimeter rises from 22.. Express your answer using two significant figures. ANSWER: m= g Exercise 6. Part A Find the food caloric content of peanut butter.8 kJ/mol ). ANSWER: ∆Hf∘ = kJ/mol Part B Use this value to calculate the mass of ice required to cool 395 mL of a beverage from room temperature (25.0 ∘ C .101 Part A Use standard enthalpies of formation to calculate the standard change in enthalpy for the melting of ice. Assume that the specific heat capacity and density of the beverage are the same as those of water.109 ∘ One tablespoon of peanut butter has a mass of 15 g . (The ∆Hf∘ for H2 O(s) is -291.2 C ..com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 31 of 32 . More Questions Exercise 6.Chapter 6 Objectives 1/16/16. It is combusted in a calorimeter whose heat capacity is 120 kJ/ C . 12:34 PM 3CaO(s) + P2 O5 (l)→Ca3 (PO 4) 2 (s) 3Ca(s) + 2P(s) + 4O2 (l)→Ca3 (PO4 ) 2 (s) 3Ca(s) + 2P(s) + 4O2 (g)→Ca3 (PO4 )2 (s) 3CaO(s) + P2 O5 (s)→Ca3 (PO4 )2 (s) A message from your instructor. Express your answer using two significant figures. Express your answer using two significant figures.masteringchemistry.4 C to 25.0 ∘ C ) to 0. ANSWER: q= Cal/g https://session. You received 3 out of a possible total of 54 points.123 ∘ An ice cube of mass 8. whose temperature is 85 C and which contains 110 g of liquid. Assume the specific heat capacity of the coffee is the same as that of water. 12:34 PM Exercise 6.masteringchemistry. Express your answer using two significant figures. https://session. Part A Find the temperature of the coffee after the ice melts. The heat of fusion of ice (the heat associated with ice melting) is 6.5 g at temperature 0∘ C is added to a cup of coffee. ANSWER: T = ∘C Score Summary: Your score on this assignment is 5.6%.Chapter 6 Objectives 1/16/16.com/myct/assignmentPrintView?displayMode=studentView&assignmentID=3900617 Page 32 of 32 .0 kJ/mol .