The **rate constant** $k$ in a rate law equals the rate of reaction when:
- All reactant concentrations are zero
- All reactant concentrations are unity
- Temperature is zero kelvin
- Time is zero
Show answer and solution
Correct answer: B. All reactant concentrations are unity
Putting unit concentrations into rate = $k[A]^x[B]^y$ gives rate = $k$.
**So $k$ is the rate at unit concentrations of all reactants.**