chem exam 2

• instantaneous rate: the reaction rate at a particular time as opposed to the average rate over an interval of time
• rate law: an equation that relates the reaction rate of the concentrations of reactants (and sometimes the products also)
• rate constant: a constant of proportionality between the reaction rate and the concentrations of reactants that appear in the rate law
• reaction order: the power to which the concentration of a reactant is raised in a rate law
• overall reaction order: the sum of the reaction orders of all the reactant appearing in the rate expression
• first-order reaction: rate depends on concentration of a single reactant raised to the first power
• second-order reaction: the rate depends either on a reactant concentration raised to the 2nd power, or on the concentrations of 2 reactants raised to the first power
• zero-order reaction: the rate of disappearance of A is not independent of [A]
• half-life: the time required for the concentration of a reactant to reach half its initial value
• collision model: model of reaction rates based on the idea that molecules must collide to react
• activation energy: the minimum energy required to initiate a chemical reaction
• frequency factor (A): a term in the Arrhenius equation that is related to the frequency of collision and the probability that the collisions are favorably oriented for reaction
• reaction mechanism: a detailed picture or model of how the reaction occurs; the order in which the bonds are broken and formed and the changes in relative positions of atoms as the reaction proceeds
• elementary reactions: a process in a chemical reaction that occurs in a single step
• molecularity: the number of molecules that participate as reactants in an elementary reaction
• unimolecular: an elementary reaction that involves a single molecule
• bimolecular: an elementary reaction that involves two molecules
• termolecular: elementary reaction that involves the simultaneous collision of three molecules (very rare)
• intermediate: a substance formed in one elementary step of a multistep mechanism and consumed in another

  (neither a reactant nor an ultimate produce of the overall reaction)
• rate-determining step: the slowest elementary step in a reaction mechanism