Glossary
Catalyst
A substance that increases the rate of a chemical reaction without being consumed in the process.
Example:
Enzymes act as biological catalysts, speeding up vital reactions in your body, like breaking down food.
Elementary Step
An individual molecular event that occurs in a single collision or decomposition within a reaction mechanism.
Example:
The collision between two NO₂ molecules to form NO and NO₃ is an elementary step in some proposed mechanisms.
Equilibrium (Keq)
A state where the rates of the forward and reverse reactions are equal, resulting in no net change in reactant and product concentrations.
Example:
In a saturated sugar solution, the rate at which sugar dissolves equals the rate at which it crystallizes, reaching a dynamic equilibrium.
Intermediate
A species that is formed in one elementary step of a reaction mechanism and then consumed in a subsequent step.
Example:
In the decomposition of H₂O₂, HO• radicals can be formed as intermediates before reacting further.
Mechanism
A detailed, step-by-step description of how reactants transform into products in a chemical reaction.
Example:
Understanding the mechanism of ozone depletion helps scientists develop strategies to protect the atmosphere.
Rate Law
An equation that expresses the relationship between the rate of a reaction and the concentrations of its reactants.
Example:
For a reaction, if doubling [A] quadruples the rate, the rate law likely includes [A]².
Rate-Determining Step (RDS)
The slowest elementary step in a reaction mechanism, which limits the overall rate of the reaction.
Example:
If a multi-step assembly line has one very slow machine, that machine represents the rate-determining step for the entire production.
Reaction Order
The exponent to which a reactant's concentration is raised in the rate law, indicating how its concentration affects the reaction rate.
Example:
If a reaction is second order with respect to reactant X, then doubling [X] will quadruple the reaction rate.