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 $2.0{\text{mol L}}^{-1}$, how much time does it take for its concentration to come from $0.50\text{to}0.25{\text{mol L}}^{-1}$ if it is a zero-order reaction?

• A. $4\text{hr}$
• B. $0.5\text{hr}$
• C. $0.25\text{hr}$
• D. $1\text{hr}$

Answer 1

The correct option is C $0.25\text{hr}$

For zero order reaction $k=\frac{x}{t}\to \left(1\right)$
Where x=amount decomposed
For a zero order reaction,
$k=\frac{[A{]}_0}{2t_{1/2}}$
$\Rightarrow k=\frac{2}{2\times 1}=1$
Since,$[A{]}_0=2\text{M},t_{1/2}=1\text{hr};k=1$
From equation (1),
$t=\frac{0.25}{1}=0.25\text{hr}$