Question

A first order reaction is 90% complete in 100 seconds. The rate constant is

(a) 0 s^-1
(b) 0.693 × 10^-2 s^-1
(c) 2.303 × 10^-2 s^-1
(a) 0.01 s^-1​

Answer 1

Answer:

Option B.

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Answer 2

Given :

Time taken to complete 90% reaction = 100 sec

To Find ;

Rate constant of the reaction

Solution :

Let 'a' be the initial concentration of the reactant

So, Concentration of the reactant after 90% completion of the reaction

                                                                                                    =  (a - $\frac{90a}{100}$)

For a first order reaction,

Rate constant (K)   = $\frac{2.303}{Time}$ ㏒ $\frac{a}{(a - \frac{90a}{100}) }$  

                               = $\frac{2.303}{100}$ ㏒ $\frac{100 a}{10a}$

                               =  0.02303 × 1

                               =  2.303 × 10⁻² sec⁻¹

Therefore, the rate constant of the given first order reaction is found to be 2.303 × 10⁻² sec⁻¹            

Hence, option (c) is correct.