Question

First order reaction is 50% complete in 120 minutes how long it will take from 19 and completion of the reaction

Answer 1

Firstly find out rate of reaction K using,

K=(2.303/60) * log (100/40)

Now take this k, which come out to be 0.0152 per minute.

For finding time for 50%, you can use any of the 2 approach:

1) you can use the same formual above and substitute the value of k to find time, here log will have different values.

t= (2.303/0.0152)*log(100/50)

t= 45.6 minutes.

2) you can use half life formula for first order reaction.

t=0.693/k

t=0.693/0.0152

t=45.6 minutes.

I hope this answers the question.