Chemical Kinetics Class 12 Notes - Chapter 4

Study of chemical reactions concerning the rate of reaction, the formation of intermediates, rearrangement of atoms, and the effect of different variables is called chemical kinetics. Factors affecting rate of reaction are the catalyst concentration of reactants, and temperature. The rate of reaction cannot be predicted but has to be determined experimentally. Rate law gives the mathematical representation of the rate of reaction.

Rate Constant

The power of concentration of the reactant in the rate law equation is the order of a reaction with respect to a reactant. Therefore to calculate the order of a reaction, add the powers of concentrations of all the different reactants in the equation. The order of reaction, as well as the rate constant, can be determined by the rate law.

Arrhenius Equation

In the year 1899, two concepts were combined to get the Arrhenius equation. The combined concepts are the Boltzmann distribution law and activation energy.

k = A.e–Ea/RT

Ea is the activation energy

A is Arrhenius factor

The above relation was got by Swedish chemist Svante Arrhenius and hence named after him.

Few Important Questions

  1. Calculate the rates of production of H2 and N2 if the decomposition of NH3 on a platinum surface is zero order reaction. k = 2.5 × 10–4 mol–1 L s–1
  2. The given equation log k = 14.34 – 1.25 × 104K/T is the rate constant for the first order decomposition of H2O2. Find Ea and temp at which its half period will be equal to 256 minutes.
  3. Show that, for a first-order reaction, the time needed to complete 99 percent is double the time needed to complete a 90 percent reaction.
  4. Calculate the half-life of a first-order reaction for the rate constant 200 s–1

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