# Chemistry Class 12 NCERT Solutions: Chapter 4 Chemical-Kinetic Part 7

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Q: 12. The reaction between A and B is first order with respect to and zero order with respect to B. Fill in the blanks in the following table:

Experiment | Initial rate | ||

I | |||

II | - | ||

III | - | ||

IV | - |

The given reaction is of the first order with respect to A and of zero order with respect to B.

Therefore, the rate of the reaction is given by,

⇒ Rate = k [A]

From experiment I, we obtain

From experiment II, we obtain

From experiment III, we obtain

From experiment IV, we obtain

Q: 13. Calculate the half-life of a first order reaction from their rate constants given below: (i)

(ii)

(iii)

Answer:

(i) Half-life,

(ii) Half-life,

(iii) Half-life,

Q: 14. The half-life for radioactive decay of is years. An archaeological artifact containing wood had only of the found in a living tree. Estimate the age of the sample.

Answer:

Here,

It is known that,

Hence, the age of the sample is years