Question

80% of a first order reaction was completed in 70 min. How much time will it take for 90% completion of a reaction?

• A. 114 min
• B. 140 min
• C. 100 min
• D. 200 min

Answer 1

The correct option is C 100 min

Using $k_1=\frac{2.303}{t}log\frac{a}{a-x}$, we can find out the value of K. Using K time required for 90% reaction can be calculated.

By putting values in the above equation, we will get

$K=\frac{2.303}{70}log\frac{1}{0.2}=0.023$

Now, again using the same equation as above, but for 90% completion, we can calculate the time.

$t=\frac{2.303}{0.023}log\frac{1}{0.1}$

So, we get time $=100min$.