Chemical reaction rates
The rate of a reaction can be expressed either in terms of the decrease in the amount of a reactant or
the increase in the amount of a product per unit time. Relations between different rate expressions for a
given reaction are derived directly from the stoichiometric coefficients of the equation representing the
reaction.
Factors affecting reaction rates
The rate of a chemical reaction is affected by several parameters. Reactions involving two phases
proceed more rapidly when there is greater surface area contact. If temperature or reactant
concentration is increased, the rate of a given reaction generally increases as well. A catalyst can increase
the rate of a reaction by providing an alternative pathway with a lower activation energy.
Rate laws
Rate laws (differential rate laws) provide a mathematical description of how changes in the
concentration of a substance affect the rate of a chemical reaction. Rate laws are determined
experimentally and cannot be predicted by reaction stoichiometry. The order of reaction describes how
much a change in the concentration of each substance affects the overall rate, and the overall order of a
reaction is the sum of the orders for each substance present in the reaction. Reaction orders are typically
first order, second order, or zero order, but fractional and even negative orders are possible.
Integrated rate laws
Integrated rate laws are mathematically derived from differential rate laws, and they describe the time
dependence of reactant and product concentrations.
The half-life of a reaction is the time required to decrease the amount of a given reactant by one-half. A
reaction’s half-life varies with rate constant and, for some reaction orders, reactant concentration. The
half-life of a zero-order reaction decreases as the initial concentration of the reactant in the reaction
decreases. The half-life of a first-order reaction is independent of concentration, and the half-life of a
second-order reaction decreases as the concentration increases.
Collision theory
Chemical reactions typically require collisions between reactant species. These reactant collisions must
be of proper orientation and sufficient energy in order to result in product formation. Collision theory
provides a simple but effective explanation for the effect of many experimental parameters on reaction
rates. The Arrhenius equation describes the relation between a reaction’s rate constant, activation
energy, temperature, and dependence on collision orientation.
The rate of a reaction can be expressed either in terms of the decrease in the amount of a reactant or
the increase in the amount of a product per unit time. Relations between different rate expressions for a
given reaction are derived directly from the stoichiometric coefficients of the equation representing the
reaction.
Factors affecting reaction rates
The rate of a chemical reaction is affected by several parameters. Reactions involving two phases
proceed more rapidly when there is greater surface area contact. If temperature or reactant
concentration is increased, the rate of a given reaction generally increases as well. A catalyst can increase
the rate of a reaction by providing an alternative pathway with a lower activation energy.
Rate laws
Rate laws (differential rate laws) provide a mathematical description of how changes in the
concentration of a substance affect the rate of a chemical reaction. Rate laws are determined
experimentally and cannot be predicted by reaction stoichiometry. The order of reaction describes how
much a change in the concentration of each substance affects the overall rate, and the overall order of a
reaction is the sum of the orders for each substance present in the reaction. Reaction orders are typically
first order, second order, or zero order, but fractional and even negative orders are possible.
Integrated rate laws
Integrated rate laws are mathematically derived from differential rate laws, and they describe the time
dependence of reactant and product concentrations.
The half-life of a reaction is the time required to decrease the amount of a given reactant by one-half. A
reaction’s half-life varies with rate constant and, for some reaction orders, reactant concentration. The
half-life of a zero-order reaction decreases as the initial concentration of the reactant in the reaction
decreases. The half-life of a first-order reaction is independent of concentration, and the half-life of a
second-order reaction decreases as the concentration increases.
Collision theory
Chemical reactions typically require collisions between reactant species. These reactant collisions must
be of proper orientation and sufficient energy in order to result in product formation. Collision theory
provides a simple but effective explanation for the effect of many experimental parameters on reaction
rates. The Arrhenius equation describes the relation between a reaction’s rate constant, activation
energy, temperature, and dependence on collision orientation.
