The first order reaction has a rate constant of 3.0x10^-3 s^-1. The time required for the r eaction to be 75% complete is:

Question

95.8s
201s
231s
462s
41.7s

Answer 1

For a first-order reaction,
eg. A -> B
the rate of reaction is:
rA=dcA/dt=-kA*cA
If you integrate this, you get:
cA=cAo*exp(-kA*t)

Need to solve for t when cA/cAo=(1-0.75)=0.25

ln(cA/cAo)=-kA*t
t=ln(0.25)/(3.0*10^-3)
=462 s