Question

How to find rate constant for first order reaction?

Answer 1

A reaction is said to be first order if its rate is determined by the change of one concentration term only.

One can say that  a first order reaction is one whose rate varies as 1st power of the concentration of the reactant i.e. the rate increases as number of times as the number of times the concentration of reactant is increased.

Consider the reaction

A → products

Let

[A]O   = Initaial Concentration of A

[A]t = The concentration of A after time t

For  the reaction to be of  first order..



...(i)

Intigrating this equation



we get

ln [A] - ln[A]o = -K(t-0)



…...... (ii)

...(iii)

....(iv)

On comparing the equation number (ii) with equation of straight line i.e. y=mx+c we come to know that , If we plot a graph between log [A]o/[A] vs t, the slope of line= k/2.303