k for a zero-order reaction is 2 × 10–2 mol L–1 s–1. If the concentration of the reactant after 25 s is 0.5 M, the initial concentration must have been:
Answer & explanation
Correct answer: option 4
The correct answer is option 4. 1.0 M.
Given,
$k= 2 × 10^{−2}\text{mol L}^{1} s^{−1}$
$t= 25 sec$
Final concentration, $[A] = 0.5 M$
Since it is a zero-order reaction, so we know
$k = \frac{1}{t}\left([A]_0 − [A]\right)$
$kt = [A]_0 − [A] $
$⇒ 2 × 10^{−2} × 25 = [A]_0 − 0.5$
$⇒ 0.5 = [A]_0 − 0.5$
$[A]_0 =1.0 M$