The rate constant for a zero order reaction was found to be $1.0 × 10^{-3}\ mol\, L^{-1}\,s^{-1}$. How long will 1.0 mol of the reactant take to reduce to 0.5 mol in one liter flask?

500 s

The correct answer is Option (1) → 500 s

For a zero-order reaction, the integrated rate law is:

$[A] = [A]_0 – kt$

Given:

• Initial concentration, $[A]_0 = \frac{1.0\ \text{mol}}{1\ \text{L}} = 1.0\ \text{M}$
• Final concentration, $[A] = \frac{0.5\ \text{mol}}{1\ \text{L}} = 0.5\ \text{M}$
• Rate constant, $k = 1.0 \times 10^{-3}\ \text{mol L}^{-1}\text{s}^{-1}$

Substitute:

$0.5 = 1.0 - (1.0 \times 10^{-3})t$

$t = \frac{1.0 - 0.5}{1.0 \times 10^{-3}} = \frac{0.5}{10^{-3}} = 500\ \text{s}$