The reaction :
`Xrarr ` Product
follows first order kinetics . In 40 minutes the concentration of X changes from 0.1 to 0.025 M. Then the rate of reaction when concentrartion of X is 0.01 M is :

Options

A. `1.73xx10^(-4) "M min"^(-1)`
B. `3.47xx10^(-5) "M min"^(-1)`
C. `3.47xx10^(-4)"M min"^(-1)`
D. `1.73xx10^(-5) "M min"^(-1)`

Answer

C

Explanation

( C ) For a first order reaction ,
`k = (k_(2))/(k_(1))= (2.303)/(40) "log" (0.1)/(0.025) `
`= (2.303)/(40) "log" 4 = (2.303)/(40) xx0.6020`
`= 0.0347 "min"^(-1)`
Now at 0.01 M concentration
Rate = k `[A] = 0.347 xx0.01`
`3.47 xx10^(-4) "mol L"^(-1) "min"^(-1)`