Chemistry Reaction Rates

Study Notes

A rate measures how much something changes within a specified amount of time.
In chemistry, the rate of a chemical reaction (reaction rate) is expressed as the change in the amount of reactant or product per unit time.

Atoms, ions, and molecules react to form products when they collide if they have enough kinetic energy.
The minimum energy required for colliding particles to react is called the activation energy.
An activated complex (or transition state) is an unstable arrangement of atoms that forms briefly at the peak of the activation-energy barrier.

Temperature: raising the temperature usually increases the reaction rate, while lowering it slows it down.
Concentration: increasing the concentration of reactants increases the frequency of collisions, leading to a higher reaction rate.
Particle size: smaller particles have a greater surface area, increasing the reaction rate.
Catalysts: substances that increase the reaction rate without being used up during the reaction, permitting reactions to proceed along a lower energy path.

The rate at which A forms B can be expressed as the change in A with time.
The rate law is an expression for the rate of a reaction in terms of the concentration of reactants.
The specific rate constant (k) in a rate law is large if products form quickly and small if they form slowly.

A first-order reaction is one in which the rate is directly proportional to the concentration of only one reactant.
The overall order of a reaction is the sum of the exponents for the individual reactants.

An elementary reaction is a reaction in which reactants are converted to products in a single step.
The series of elementary reactions or steps that take place during a complex reaction is called a reaction mechanism.
An intermediate is a product of one step in a reaction mechanism and a reactant in the next step.
The slowest step determines the rate of the overall reaction.