Question

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

Answer 1

for 75% completion it needs 2half lifes

so from the question half life is 50minutes

for 87.5%completion it needs 3half lifes so time taken will be 3×50=150min

Answer 2

Answer:

The time is 50 minutes.

Explanation:

Given that,

First order reaction is 75% completed in 100 minutes.

We need to calculate the time

Using equation is

$t=\dfrac{2.303}{k}\times\dfrac{log R_{0}}{R}$

If reaction is 75% complete

Put the value into the formula

$100=\dfrac{2.303}{k}\times\dfrac{log 100}{25}$

$100=\dfrac{2.303}{k}\times log 4$

$k= \dfrac{2.303\times log 4}{100}$

$k=0.01386$

Now, at 87.5% $t = t_{\frac{1}{2}}$

$t_{\frac{1}{2}}=\dfrac{0.693}{k}$

Put the value into the formula

$t_{\frac{1}{2}}=\dfrac{0.693}{0.01386}$

$t_{\frac{1}{2}}=50\ min$

Hence, The time is 50 minutes.