Final answer:
The units for the rate constant k depend on the order of the reaction: For zeroth-order, it's mol·L⁻¹·s⁻¹; for first-order, it's s⁻¹; for second-order, it's L·mol⁻¹·s⁻¹; for third-order, it's L²·mol⁻²·s⁻¹.
Step-by-step explanation:
For each reaction order, the proper units for the rate constant (k) vary according to the overall reaction's order due to the need for the units of rate to always be moles per liter per second (mol·L⁻¹·s⁻¹).
- Zero order: The unit for the rate constant of a zeroth-order reaction is moles per liter per second (mol·L⁻¹·s⁻¹), because the rate is independent of the concentration of reactants.
- First order: The unit for the rate constant of a first-order reaction is per second (s⁻¹), as the rate is directly proportional to the concentration of one reactant.
- Second order: The unit for the rate constant of a second-order reaction is liters per mole per second (L·mol⁻¹·s⁻¹), because the rate is proportional to the square of the concentration of one reactant.
- Third order: The unit for the rate constant of a third-order reaction is liters squared per mole squared per second (L²·mol⁻²·s⁻¹), as the rate depends on the cube of the concentration of one reactant.
To determine the reaction order from experimental data, one typically compares initial reaction rates with corresponding changes in initial concentrations and applies the differential or integrated rate law.