Question

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

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

Answer 1

The correct option is B $150min$

$\underset{Remaining}{\underset{}{100\%}}\underset{1halftime}{\overset{after}{\to }}\underset{Remaining}{\underset{}{50\%}}\underset{2halftime}{\overset{after}{\to }}\underset{Remaining}{\underset{}{25\%}}\underset{3halftime}{\overset{after}{\to }}\underset{Remaining}{\underset{}{12.5\%}}$

After 2 half times $75\%$ reactions is complete

$\Rightarrow$ half time $=50$ minutes

.

After 3 half times $87.5\%$ reactions is complete.

$\Rightarrow 3\times 50$ minutes $=150$ Minutes.