Ch6. Kinetics
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Definitions
Activated complex: Created during a bimolecular process. Not a chemical substance which can be isolated, but consists of reacting particles in which bonds are in the process of being broken and formed. Can break down to form either the products or back to the original reactants.
Activation energy: The minimum amount of energy required for a reaction to occur between two particles. The other requirement is that the particles have to have an appropriate geometry of collision.
Arrhenius equation: An equation showing the relationship between the temperature and the rate constant. K=Ae(-Ea/RT)
Bimolecular process: A reaction step when two species collide and interact.
Catalyst: Provide an alternative pathway for a reaction such that the activation energy required to reach the activation complex is lowered.
Can be divided into two types: homogenous catalysts are in the same phase as the reactants, while heterogeneous ones are in a different phase. Heterogeneous catalysts tend to work by bring the reactant particles into close alignment by adsorbing them onto the catalytic surface.
Half-life: The time taken for the concentration of the reactant to fall to half of its initial value.
Maxwell-Boltzmann distribution: Graph showing the distribution of kinetic energies among molecules.
Molecularity: Number of species taking part in any specified step in the reaction.
Order of reaction: The rate is always proportional to the concentration of a reactant raised to a power, where the power is the order of the reaction with respect to that reactant.
Rate constant: The constant of proportionality in the rate expression.
Rate expression: An equation that shows the relationship between the concentrations of the reactants and the rate of the reaction.
Every species in the rate expression must occur in the rate determining step or in an equilibrium occurring before it.
Rate of reaction: The rate of increase of concentration of one of the products or the rate of decrease of concentration of one of the reactants.
Rate-determining step: The slowest step of a reaction (or the step with the highest activation energy). This determines the rate of the entire reaction.
Unimolecular process: A process in which a single species breaks down into two or more products.
•How to determine the order of a reaction [.pdf]
