# Chemistry Class 12 NCERT Solutions: Chapter 4 Chemical-Kinetic Part 8

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Q: 15. The experimental data for decomposition of in gas phase at are given below:

(i) Plot against t

(ii) Find the half-life period for the reaction.

(iii) Draw a graph between and t.

(iv) What is the rate law?

(v) Calculate the rate constant.

(vi) Calculate the half-life period from k and compare it with (ii).

(i)

(ii) Time corresponding to the concentration, is the half-life. From the graph, the half-life is obtained as .

(iii)

t(s) | ||

0 | ||

400 | ||

800 | ||

1200 | ||

1600 | ||

2000 | ||

2400 | ||

2800 | ||

3200 |

(iv) The given reaction is of the first order as the , is a straight line. Therefore, the rate law of the reaction is

(v) From the plot, we obtain

Again, slope of the line of the plot is given by

Therefore, we obtain,

(vi) Half –life is given by,

This value, 1483 is very close to the value that was obtained from the graph.

Q: 16. rate constant for a first order reaction is . How much time will it take to reduce the initial concentration of the reactant to its value?

Answer:

It is known that,

Hence, the required time is