Chemistry Chapter 18

activated complex

an unstable arrangement of atoms that exists momentarily at the peak of the activation-energy barrier; an intermediate or transitional structure formed during the course of a reaction

activation energy

the minimum energy colliding particles must have in order to react

chemical equilibrium

a state of balance in which the rates of the forward and reverse reactions are equal; no net change in the amount of reactants and products occurs in the chemical system

collision theory

atoms, ions, and molecules can react to form products when they collide, provided that the particles have enough kinetic energy

common ion

an ion that is common to both salts in a solution; ex: in a solution of silver nitrate and silver chloride, Ag+ would be the _____

common ion effect

a decrease in the solubility of an ionic compound caused by the addition of a common ion

elementary reaction

a reaction in which reactants are converted to products in a single step

entropy

(S) a measure of the disorder of a system; systems tend to go from a state of order (low ___) to a state of maximum disorder (high ___)

equilibrium constant

(Keq) the ratio of product concentrations to reactant concentrations at equilibrium, with each concentration raised to a power equal to the number of moles of that substance in the balanced chemical equation

equilibrium position

the relative concentrations of reactants and products of a reaction that has reached equilibrium; indicated whether the reactants or products are favored in the reversible reaction

first-order reaction

a reaction in which the reaction rate is proportional to the concentration of only one reactant

free energy

the energy available to do work

Gibbs free-energy change

the maximum amount of energy that can be coupled to another process to do useful work

inhibitor

a substance that interferes with the action of a catalyst

intermediate

a product of one of the steps in a reaction mechanism; it becomes a reactant in the next step

law of disorder

it is a natural tendency of systems to move in the direction of maximum chaos or disorder

Le Chatelier's principle

when a stress is applied to a system in dynamic equilibrium, the system changes in a way that relieves the stress

nonspontaneous reaction

a reaction that does not favor the formation of products at the specified conditions

rate

describes the speed of change over an interval of time

rate law

an expression relating the rate of a reaction to the concentration of the reactants

reaction mechanism

a series of elementary reactions that take place during the course of a complex reaction

reversible reaction

a reaction in which the conversion of reactants into products and the conversion of products into reactants occur simultaneously

solubility product constant

(Ksp) an equilibrium constant applied to the solubility of electrolytes; it is equal to the product of the concentrations of the ions each raised to a power equal to the coefficient of the ion in the dissociation equation

specific rate constant

a proportionality constant relating the concentrations of reactants to the rate of the reaction

spontaneous reaction

a reaction that favors the formation of products at the specified conditions; spontaneity depends on enthalpy and entropy changes

transition state

a term sometimes used to refer to the activated complex