What does the half-life of a zero-order reaction depend on?

• A. Temperature only
• B. The final concentration [A]∞
• C. It is constant independent of [A]0
• D. Initial concentration [A]0 and rate constant k

Answer: (D)

For a zero-order reaction, the rate is constant (rate = k), so the concentration falls linearly with time: [A] = [A]0 − kt. The half-life is the time needed for [A] to drop to half its initial value, so set [A] = [A]0/2 and solve for t:

[A]0/2 = [A]0 − kt1/2 → kt1/2 = [A]0/2 → t1/2 = [A]0/(2k).

This shows the half-life depends on the initial concentration [A]0 and the rate constant k. Temperature affects k (through the Arrhenius relationship), so it influences t1/2 indirectly, but the direct dependence is on [A]0 and k.