Time required for the concentration of a reactant to fall to one half of its initial value is called what?

• A. Rate Law
• B. Activated complex
• C. Arrhenius
• D. Half-life

Answer: (D)

The term being tested is half-life in kinetics. It exactly means the time required for the concentration of a reactant to drop to half of its initial value, usually denoted t1/2. This concept is a straightforward way to describe how quickly a reactant is consumed. The other options describe different ideas: a rate law tells how the rate depends on concentrations, the activated complex is the transient high-energy state at the top of the energy barrier, and Arrhenius relates to how temperature affects the rate constant. So half-life is the precise label for the time needed to reach half of the starting concentration.