Units depend on overall order (e.g., M⁻¹s⁻¹ for 2nd order)
Rate Law Expression:
Rate = k × [A]
Rate = k × [A]^m × [B]^n
General rate law expression
k = rate constant
[A], [B] = reactant concentrations
m, n = reaction orders (experimentally determined)
Overall order = m + n
What is a Rate Law?
The rate law expresses how the reaction rate depends on the concentrations of reactants. It is experimentally determined and cannot be inferred from stoichiometry alone.
Reaction Order
The order with respect to each reactant indicates how the rate changes with concentration. A first-order reaction doubles in rate when concentration doubles.
Rate Constant (k)
The rate constant is specific to each reaction and changes with temperature. Its units depend on the overall reaction order.
Important Note
Rate law expressions are experimentally determined. Calculated rates are theoretical and assume ideal reaction conditions. The reaction order cannot be determined from balanced chemical equations and must be found experimentally.