Question

What is first order reaction? Give two examples of first order reaction.

Obtain an experssion for the rate constant of a first order reaction​

Answer 1

Explanation:

First-order reactions are very common. We have already encountered two examples of first-order reactions: the hydrolysis of aspirin and the reaction of t-butyl bromide with water to give t-butanol. Another reaction that exhibits apparent first-order kinetics is the hydrolysis of the anticancer drug cisplatin.

Rate constant of a first order reaction: The reaction in which, the overall rate of the reaction is proportional to the first power of concentration of one of the reactants only are called first order reaction.

A→k1 products

Rate of reaction =dt−d[A]=k1[A]10

where k1 is the rate constant of the first order reaction.

At the beginning of the reaction, time ′t′=0, let the concentration of A be 'a' mole lit−1. After the reaction has proceeded for some time 't', let the concentration of A that has reacted be x mole lit−1. The concentration of unreacted A remaining at time 't' will be (a−x) mole lit−1. The rate of the reaction will be dx/dt. For a first order reaction,

rate =dx/dt=k1(a−x) ...... (1)

Integrating (1), both sides

∫(a−x)dx=k1∫dt

Which is −ln(a−x)=k1t+c  ...... (2)

C= integration constant.

at time, t=0,x=0

In equation (2)

−ln(a−0)=k1×0+c

or

c=ln a

Substituting c value in equation (2)

−ln(a−x)=k1t−ln 

Answer 2

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A first-order reaction is a reaction that proceeds at a rate that depends linearly on only one reactant concentration.

Explanation:

For example, the rate law Rate=k[NO]2[O2] Rate = k [ NO ] 2 [ O 2 ] describes a reaction which is second-order in nitric oxide, first-order in oxygen, and third-order overall. This is because the value of x is 2, and the value of y is 1, and 2+1=3.

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