Glossary
First Order
Describes a reaction where the rate is directly proportional to the concentration of a specific reactant raised to the power of one.
Example:
If a decomposition reaction is first order in reactant A, doubling the concentration of A will exactly double the reaction rate.
Overall Reaction Order
The sum of the individual reaction orders for all reactants in a rate law, representing the total dependence of the reaction rate on reactant concentrations.
Example:
For the rate law R = k[A]²[B]¹, the overall reaction order is 2 + 1 = 3.
Rate Constant (k)
A proportionality constant in the rate law that relates the reaction rate to reactant concentrations; its value is specific to a given reaction at a particular temperature.
Example:
If a reaction has a rate constant (k) of 0.05 M⁻¹s⁻¹, it indicates how efficiently reactants are converted to products at that temperature.
Rate Law
An equation that expresses how the rate of a chemical reaction depends on the concentrations of its reactants, determined experimentally.
Example:
For the reaction A + B → C, a common rate law might be R = k[A]¹[B]², showing the reaction's speed depends on A and B concentrations.
Reaction Order
The exponent to which a reactant's concentration is raised in the rate law, indicating how the reaction rate is affected by changes in that reactant's concentration.
Example:
If a reaction is second reaction order with respect to reactant X, doubling [X] would quadruple the reaction rate.
Second Order
Describes a reaction where the rate is proportional to the square of the concentration of a specific reactant, or to the product of the concentrations of two different reactants.
Example:
If a reaction is second order with respect to reactant B, tripling the concentration of B would increase the reaction rate by nine times.
Zeroth Order
Describes a reaction where the rate is independent of the concentration of a specific reactant; changing its concentration has no effect on the reaction rate.
Example:
In a zeroth order reaction, even if you double the amount of reactant C, the rate of the reaction will remain unchanged, often due to saturation of a catalyst.