A16126REQUIREMENTS: SI UNIT BOOKLET GRID GRAPH PAPER THE UNIVERSITY OF BIRMINGHAM SCHOOL OF CHEMISTRY Degree of MSci/BSc with Honours Chemistry Chemistry with Analytical Science Chemistry with Bioorganic Chemistry Chemistry with Environmental Science Chemistry with Psychology Chemistry with Pharmacology Chemistry with Business Management Chemistry with French Chemistry with Study in Continental Europe CHM1C4: Introduction to Physical Chemistry 03 15598 May/June 2004 1.5 hrs PART A contributes a maximum of 40% to this examination. Students may answer any question or parts of questions to achieve their 40% (40 marks). Students are advised to spend 40 minutes on Part A questions. PART B contributes 60% to this examination. Students are required to answer two (2) whole questions. Students are advised to spend 50 minutes on Part B questions. EACH QUESTION MUST BE ANSWERED IN A SEPARATE BOOK AND THE NUMBER CLEARLY STATED ON THE FRONT OF THE BOOK. All these books should be assembled with a completed grid (obtainable from an invigilator) and securely fastened together. Calculators may be used in this examination but must not be used to store text. Calculators with the ability to store text should have their memories deleted prior to the start of the examination. Turn over ion-dipole and give an example of each.62 × 10-78 J m6. (i) Calculate the number of moles of gas present. A1.CHM1C4 2 Part A PART A contributes a maximum of 40% to this examination.20 dm3 at a pressure of 1.4 nm apart. Students may answer any question or parts of questions to achieve their 40% (40 marks). (4 marks) (b) The potential energy V(R) for the interaction between two molecules. (6 marks) A2. (a) Explain why the emission spectrum of the hydrogen atom contains four discrete bands in the visible region of the electromagnetic spectrum (λ = 400–700 nm) rather than a continuum. which are separated by a distance R. is given by the equation: V(R) = − C R6 Calculate the potential energy of interaction between two molecules of HCl which are 0. (ii) What will be the new pressure of the gas if the temperature is raised to 480 K while keeping the volume fixed? (6 marks) A16126 Any Calculator Turn over . (a) Place the following interactions in order of increasing strength: dipole-dipole. ion-ion.30 × 105 Pa and a temperature of 360 K. Students are advised to spend 40 minutes on Part A questions. (4 marks) (b) An ideal gas occupies a volume of 0. and for which C = 1. (10 marks) A5. What happens to the internal energy as the temperature of the system is raised? (b) Give an example of an intensive property and an extensive property. giving appropriate units for each. (a) 3 Define the internal energy. (a) Discuss the differences between a reaction intermediate and a transition state and sketch an appropriate reaction energy profile to illustrate the difference. k = A exp(-Ea /RT) Define the quantities k. (a) The temperature dependence of a bimolecular reaction can be described by the Arrhenius equation. (b) From the Arrhenius equation. Is entropy an intensive or extensive property? (10 marks) A4. U. of a system. Ea.CHM1C4 A3. and units of time in s−1. (10 marks) A16126 Any Calculator Turn over . explaining the two terms. explaining its molecular origin. R and T in the equation. (b) If the concentration of a species is measured in units of mol dm-3. For the rate law. describe qualitatively how the rate constant is predicted to vary with temperature? Describe at a molecular level the reason for this dependence. state the units for the rate of reaction. A. Rate = k [A] 2 [B] determine the units of the rate constant. CHM1C4 4 Part B PART B contributes 60% to this examination.2351 Pa m6 mol-2 and b = 3. and for argon are a = 0. Calculate the total pressure of the mixture at a temperature of 323 K. which of these two gases would you expect to behave in a more ideal manner? (2 marks) (iii) Calculate the pressure of 1 mole of argon.37 × 10-5 m3 mol-1. λ. (3 marks) (ii) Given that the values of the van der Waals constants for helium are a = 0. of this atom.98 × 10-5 m3 mol-1. and the partial pressures of each gas. Comment on the magnitude of this wavelength. (a) An atom of argon is travelling at a speed of 800 m s-1. contained in a 2 × 10-3 m3 vessel at a temperature of 300 K. Using the de Broglie equation: λ= h p calculate the wavelength.0 dm3. B1. behaving as a non-ideal gas.0034 Pa m6 mol-2 and b = 2. (5 marks) A16126 Any Calculator Turn over . (5 marks) (c) The van der Waals equation for 1 mole of a non-ideal gas may be written as: a p + V 2 [V − b] = nRT (i) State the two main assumptions made for ideal gases that do not apply for real gases. (5 marks) (b) 4 g of helium and 40 g of argon are mixed in a vessel of volume 8. Students are required to answer two (2) whole questions. Students are advised to spend 50 minutes on Part B questions. Given that the standard molar enthalpy of formation of CH3I(l) is –8. C(s) + 3/2 H2(g) + ½ I2(s) → CH3I(l) given that the standard molar entropies of CH3I(l). what is the total multiplicity of the system? (iii) By calculating the multiplicities for two different possible configurations. C(s). 131 and 117 J K-1 mol-1. H2(g) and I2(s) are 163.. are allowed to mix. referring to the concept of multiplicity. n1!n 2 !. illustrate your answer to part (i). initially in two volumes separated by a barrier. determine if the reaction occurs spontaneously as written at 298 K. You may find the following formula useful: N! W= . (7 marks) A16126 Any Calculator Turn over . (ii) For the unmixed gases.. (a) 5 Describe how the second law of thermodynamics can enable the direction of spontaneous change for a chemical process to be determined. 5.4 kJ mol-1. as shown in the figure. The system can be represented by the lattice model: Barrier Molecule A Molecule B (i) Explain why spontaneous mixing occurs once the barrier is removed from between the gases. respectively.nt ! (9 marks) (c) Calculate the entropy change for the reaction.CHM1C4 B2. (4 marks) (b) Two different gases.7. t/s p/Pa 0 10.CHM1C4 B3. confirm that the reaction follows unimolecular behaviour.8 1000 7. (9 marks) (c) What change in the data in part (b) would you expect if the temperature were raised. show that rate law can be integrated to give the time-dependent equation: ln [CH3N2CH3(g)] – ln [CH3N2CH3(g)]0 = . What are the units of the rate constant? (8 marks) (b) The variation in the partial pressure of diazomethane with time is given below at 600 K.66 (i) Starting with the rate law from part (a). write down the reaction. [CH3N2CH3(g)]0 is the concentration at t = 0 s. Explain the term unimolecular. and suggest a rate law for the reaction.25 3000 3.53 2000 5. (ii) By plotting an appropriate graph. and why? (3 marks) A16126 Any Calculator .k t where [CH3N2CH3(g)] is the concentration of diazomethane at time t. (a) 6 The decomposition of diazomethane (CH3N2CH3(g)) to produce ethane and nitrogen can be described as unimolecular. (iii) Estimate the rate constant at this temperature. and k is the rate constant.