Question

If $50$% of a reaction occurs in $100$ second and $75$% of the reaction occurs in $200$ second, the order of this reaction is:

• A. $1$
• B. $0$
• C. $2$
• D. $3$

Answer 1

The correct option is A $1$

$50$% of a reaction occurs in $100$ second and $75$% of the reaction occurs in $200$ second, the order of this reaction is 1.

Let the initial reactant concentration is 1 M.

In first 100 seconds, reactant concentration is reduced to 50% or $1\times \frac{50}{100}=0.5M$.

In second 100 seconds (total 200 seconds from start), reactant concentration is reduced to $100-75=25$% or $1\times \frac{25}{100}=0.25M$.

Thus we observe that after each 100 second period, the reactant concentration is reduced to one half. Hence, 100 seconds is the half-life period and is independent of reactant concentration. This is characteristic of the first-order reaction.