chemical kinetics

Chemical kinetics chapter at a glance Rate of reaction Average rate Instantaneous rate: Rate law : Factors affecting rate of a reaction : * Lower the activation energy , faster is the reaction. * Greater the conc. of reactant, faster is reaction . * Rate of reaction almost doubles for every 10℃ rise in temperature. *Greater the surface area of reactant , faster will be the rate of reaction..

* Higher the temperature,higher the rate of reaction. Molecularity & Order of reaction Integrated rate equations &Units of rate constant

Conc. Vs Time graphs for first & zero order reaction Half life vs. Conc. graphs . Pseudo first order reactions : Temperature dependence of the rate of reaction ' * Certain reactions are not feasible at room temperature, but occur spontaneously when temperature is raised ( by raising temp. necessary activation energy is provided ) * Rate of reaction is almost doubled when temperature increases by 10℃

The minimum energy which the colliding molecules must have in order that the collision between them may be effective is called THRESHOLD ENERGY. * Activation energy = Threshold energy -Av. kinetic of molecules Quantitatively, the effect of temperature is given by Arrhenius equation : Collision Theory of reaction rates :According to collision theory rate of reaction depends upon collision frequency and number of effective collisions (molecules possessing threshold energy ) Rate of reaction = -dx/dt = ZAB * f (f = e-E/RT )

Few Questions for practice: Q1. What is the difference between law of mass Action and rate law ? Q2.For which type of reactions order and molecularity have same value ? Q3.In Arrhenius equation what does factor e-E/RT corresponds to ? Q4.For a zero order reaction will the molecularity be equal to zero ? Q5.If half life is 25 min,amount of reactant left after 100 min will be 1/16 . [ True / False ] Q6.Photosynthesis is zero order reaction . [ True/False ] Q7.What is the unit of second order rate constant ? Q8.Write the integrated rate law equation for zero order reaction ? Q9.The thermal decomposition of HCOOH is a first order reaction with a rate constant of 2.4 x 10-3 s-1 at a certain temperature .Calculate how long will it take for three fourth of initial quantity of HCOOH to decompose .( log 0.25 = -0.6021 ). (t3/4 = 5.775 x 102 s ) Q10.What is the physical significance of energy of activation ? Explain with diagram . Q11.For the reaction : 2 N2O5 (g) → 4 NO2 (g) + O2 (g) The rate of formation of NO2 is 2.8 x 10-3 Ms-1. Calculate rate of disappearance of N2O5. (g) ( 1.4 x 10-3 M s-1 ) A12.Define the following: (a) Order of a reaction (b) Elementary step in a reaction A first order reaction had the rate constant value of 0.00510 min-1 .If we begin with 0.10 M concentration of reactant ,how much of the reactant will remain after 3.0 hours.