Question

Half life of zero order reaction is 1 hour. If initial concentration of reactant is 2.0 mol \(\text{L}^{-1}\), find the time required to decrease concentration from 0.50 to 0.25 mol \(\text{L}^{-1}\)

• A. \(0.25\) hour
• B. \(0.50\) hour
• C. \(1.00\) hour
• D. \(4.00\) hour

Hint:

For zero order, \(k = [A]_0/(2t_{1/2})\) and \(t = \Delta[A]/k\).

Answer 1

The Correct Option is A

Step 1: Use the half life to get the rate
In 1 hour the concentration falls from 2.0 to 1.0, a drop of 1.0 mol/L. So the rate is 1.0 mol L$^{-1}$ h$^{-1}$, constant.

Step 2: Apply
A fall of 0.25 mol/L takes $0.25/1.0 = 0.25$ hour, option (A).

Final Answer:
A drop of 0.25 mol/L takes 0.25 hour, option (A). \[ \boxed{0.25\ \text{h}} \]