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)

$0.25\, h$

Answer 2

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 $\left(1\right)$ $t = \frac{0.25}{1} = 0.25\,hr$