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

Answer: (C)

For a zero order reaction $k = \frac{x}{t }\quad\quad\to\left(1\right)$
Where x = amount decomposed
k = zero order rate constant for a zero order reaction
$k = \frac{\left[A\right]_{0}}{2t_{\frac{t}{2}}}\quad \quad \to \left(2\right)$
Since $\left[A_{0}\right] = 2M ,\, t_{1/2} = 1 \,hr; \,k = 1$
$\therefore $ from equation $\left(1\right)$
$t = \frac{0.25}{1} = 0.25\,hr$