Question

The rate constant for a zero-order reaction is $2\times {10}^{–2}{\text{mol L}}^{–1}{\text{sec}}^{–1}$, if the concentration of the reactant after $25\text{sec}$ is $0.25M$, calculate the initial concentration.

Answer 1

Given: Rate constant $\left(k\right)=2\times {10}^{–2}{\text{mol L}}^{–1}{\text{sec}}^{–1}$
Concentration at $25\text{sec}$ = $0.25\text{M}$
∴ For zero order reaction, $k=\frac{A_o-A}{t}$
$\Rightarrow 2\times {10}^{–2}=\frac{A_o-0.25}{25}$
$\Rightarrow 2\times {10}^{–2}=\frac{A_o}{25}-\frac{0.25}{25}$
$\Rightarrow 2\times {10}^{–2}=\frac{A_o}{25}-1\times {10}^{–2}$

Initial conc. $\left(A_o\right)=(3\times {10}^{–2})\times 25=75\times {10}^{–2}=0.75M$