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:


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