Question

A first order reaction is 75% completed in 100minutes. How long will it take for it's 87.5% completion?

• A. 125 min
• B. 150 min
• C. 175 min
• D. 200 min

Answer 1

The correct option is B

150 min

Explanation for the correct answer:-

Option (B) 150 min

Step 1: Given data

Amount of reaction completed$=75\%$

Time taken to complete $75\%$of the reaction$=100\min$

Step 2: Finding the time taken to complete 87.5% reaction

From the reaction above, we can see that after 2 halftimes 75% of the reaction is completed

$$\begin{gathered} \therefore \mathrm{halftime}=\frac{100}{2} \\ \Rightarrow \mathrm{halftime}=50\min \end{gathered}$$

Also, we can see that after 3 halftimes 87.5% of the reaction is completed

$$\begin{gathered} \therefore \mathrm{halftime}=50\times 3 \\ \Rightarrow \mathrm{halftime}=150\min \end{gathered}$$

Therefore, time taken to complete 87.5% reaction is option (B) 150 min