Chemistry Class 12 NCERT Solutions: Chapter 4 Chemical-Kinetic Part 2

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Q: 6. Time required to decompose to half of its initial amount is minutes. If the decomposition is a first order reaction, calculate the rate constant of the reaction.


We know that for a 1st order reaction,

It is given that


Q: 7. What will be the effect of temperature on rate constant?


The rate constant of a reaction is nearly doubled with a rise in temperature. However, the exact dependence of the rate of a chemical reaction on temperature is given by Arrhenius equation,


A is the Arrhenius factor or the frequency factor

Tis the temperature

the gas constant

is the activation energy

Q: 8. The rate of the chemical reaction doubles for an increase of in absolute temperature from . Calculate .


It is given that

We also know that the rate of the reaction doubles when temperature is increased by

Therefore, let us take the value of and that o


Now, substituting these values in the equation:

We get:

Note: There is a slight variation in this answer and the one given in the NCERT textbook.

Q: 9. The activation energy for the reaction

Is Calculate the fraction of molecules of reactants than activation energy?


In the given case:

Now, the fraction of molecules of reactants having energy equal to or greater than activation energy is given as: