The unit of rate of reaction is mol L–1s–1. It is equal to dx/dt. 3. It is always a whole number. It is also called specific reaction rate. Pseudo first-order reaction: The reaction which is bimolecular but the order is one is called pseudo first-order reaction. Arrhenius equation of reaction rate: It gives the relation between the rate of reaction and temperature. Rate law or rate equation: It is the expression which relates the rate of reaction with the concentration of the reactants.topperlearning. 2. Instantaneous rate: It is the rate of reaction when the average rate is taken over a particular moment of time. Average rate: The rate of reaction measured over a long time interval is called the average rate of reaction. Order of a reaction: The sum of the exponents (power) of the concentration of reactants in the rate law is termed the order of the reaction. 9. Molecularity of a reaction: Total number of atoms. 8.CHEMISTRY CHEMICAL KINETICS Chemical Kinetics 1.303RT 2 . It cannot be zero. It can also be zero. 6.com Ea 2. 12. ln k = ln A − Ea/RT log k = log A − www. Example: Acidic hydrolysis of ester (ethyl acetate). the rate of reaction is known as the rate constant. k 2 It is independent of initial concentration for a first-order reaction. ions or molecules of the reactants involved in the reaction is termed its molecularity. Chemical kinetics: The branch of chemistry which deals with the study of reaction rates and their mechanisms is called chemical kinetics. The constant of proportionality ‘k’ is known as the rate constant. 7. Rate of reaction: It is defined as the change in concentration of reactants (or products) in unit time. A = frequency factor. T = temperature in Kelvin. H CH3COOC2H5 H2O CH3COOH C2H5OH 11.693 called half-life of a reaction. 10. For first-order reaction t 1 . k = AeEa /RT where k = rate constant. It is never more than three. Ea = energy of activation R = gas constant. where k is the rate constant. Half-life of a reaction: The time taken for a reaction when half of the starting material has reacted is 0. 4. 5. It is equal to ∆x/∆t. Rate constant: When the concentration of reactants is unity. It can be in fractions. This happens when one of the reactants is in large excess. Activation energy (Ea): It is extra energy which must be possessed by reactant molecules so that collision between reactant molecules is effective and leads to the formation of product molecules. CHEMISTRY CHEMICAL KINETICS 13. 15. 14. The number of collisions per second per unit volume of the reaction mixture is known as collision frequency (Z). Activated complex: It is defined as an unstable intermediate formed between reacting molecules. Mechanism of reaction: The sequence of elementary processes leading to the overall stoichiometry of a chemical reaction is known as the mechanism of a reaction.topperlearning. www. It is highly unstable and readily changes into product. Rate determining step: The slowest step in the reaction mechanism is called the rate determining step.com 3 . 16. where dx is a small change in concentration and dt is the smallest interval of dt time. Order of reaction: Rate If rate law expression for a reaction is Rate = k [A]x [B]y Order of reaction = x + y Remember: Order cannot be determined with a given balanced chemical equation. Integrated rate law for zero-order reaction: R→P dx k[R]0 dt Unit of ‘k’ is mol L−1s−1 [R ] . If we plot a graph between ln[R] with time. 6. t 3. Average rate = x . where d[A] is a small change in concentration of ‘A’ and dt is a dt small interval of time. d[B] . the graph is a straight line with a slope equal to −k and the intercept is equal to [Ro].303 a k log t ax www.CHEMISTRY CHEMICAL KINETICS TOP Formulae: 1. It can be experimentally determined. and t is a large interval of time. [R o] is initial molar concentration and [R] is the final molar concentration after time ‘t’. A + B → C + D Rate of disappearance of A d[A] .com 4 .303 log o t [R] where ‘k’ is the rate constant or specific reaction rate.topperlearning. 5.[R] k= o t If we plot a graph between concentrations of R vs time. Rate law for first-order reaction: RP k [R ] 2. dt d[C] Rate of appearance of C dt d[D] Rate of appearance of D dt Rate of disappearance of B d[A] d[B] d[C] d[D] dt dt dt dt Unit of rate of reaction = mol L−1s−1 4. Half-life reaction for a zero-order reaction: t½ [R 0 ] 2k 7. where x is change in concentration. 2. we get a straight line whose slope k and intercept = ln[Ro] 2. Instantaneous rate = dx . www. Hence.693 t½ k 9. the final concentration after time ‘t’ is (a – x). log T2 T1 Ea k2 k1 2.303 pi log t (2pi -pt ) where pi is initial pressure of A pt is total pressure of gaseous mixture containing A. ‘x’ is the concentration in mol L−1 which has reacted in time ‘t’. Rate P ZAB. Arrhenius equation: k=A e-Ea/RT 11.topperlearning. C Remember: pt = pA + pB + p C 10.com 5 . 8. B.e RT Ea where ZAB represents the collision frequency of the reactants A and B.303 R T1T2 Ea 12. Half-life for a first-order reaction is 0.CHEMISTRY CHEMICAL KINETICS where ‘a’ is initial concentration in mol L−1. e RT represents the fraction of molecules with energies equal to or greater than Ea and P is called the probability or steric factor. Formula to calculate rate constant for first-order gas phase reaction of the type A(g) B(g) + C(g) k= 2.
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