Question

The time for half-life period of a certain reaction $A\to$ products is 1 hour. When the initial concentration of the reactant $A$ is 2.0 mol L${}^{-1}$, how much time does it take for its concentration to come from 0.50 to 0.25 mol L${}^{-1}$ if it is a zero-order reaction?

• A. 4 h
• B. 0.5 h
• C. 0.25 h
• D. 1 h

Answer 1

The correct option is C 0.25 h

For a zero order reaction $k=\frac{x}{t}\to \left(1\right)$
Where $x=$ amount decomposed

For a zero order reaction,
$k=\frac{[A{]}_0}{2t_{\frac{1}{2}}}$

Since $\left[A_0\right]=2M,t_{1/2}=1$ hr; $k=1$

From equation (1),

$t=\frac{0.25}{1}=0.25$ hr