Equilibrum and Rate of Reaction

The measure of speed or change over any interval of time. *Key Concept: In chemistry, the rate of chemical change or the reaction rate is usually expressed as the amount of changing reactant per unit of time.*
Collision Theory
Atoms, ions and molecules can react to form prducts when they collide with one another, provided that the colliding particles have enough kinetic energy. Particle without enough kinetic energy bounce back unchanged from a collision.
Activation Energy
The minimum amount of energy particles must have in order to react.
Activated Complex
An unstable arrangement of atoms that forms momentarily at the peak of the activation barrier.
Transition State
Another term for activated complex, in which: an unstable arrangement of atoms that forms momentarily at the peak of the activation barrier.
Factors Affecting Rate of Reaction
*Key Concept: The rate of a chemical reaction depends upon temperature, concentration, particle size, and use of a catalyst.*
A substance that interferes with the action of a catalyst. Reactions slow or stop if a catalyst is poisioned.
Reversible Reaction
A reaction in which the conversion of reactants to products and the conversion of products to reactants happens simultaneously.
Chemical Equilibrium
When, in a reversible reaction, the changes of forward and backward reactions are happening at equal rates. *Key Concept: At chemical equilibrium, no net change occurs in the actual amounts of the components of the system.*
Equilibrium Position
The relative concentrations of the reactants and products at equilibrium
Le Chatalier’s Principle
If a stress is applied to a system in a dynamic equilibrium, the system changes in a way that relieves the stress. *Key Concept: Stresses that upset the equilibrium of a chemical system include changes in the concentration of reactants or products, changes in temperature, and changes in pressure.*
Equilibrium Constant
The ratio of product concentrations to reactants concentrations at equilibrium, with each concentration raised to a power equal to the number of moles of that substance in the balanced chemical equation. *Key Concept: A value of Keq greater than one means products are favored. A value of Keq less than one means reactants are favored.
Solubility Product Constant
The product of concentrations of each ion raised to the power of the coefficents of the ions in the dissocation equation. *Key COncept: The smaller numerical value of the solubility product constant, the lower the solubility of the compound.*
Common ion
An ion which is found both in a salt and in the solution.
Common ion effect
The lowering of the solubility of an ion due to the addition of a common ion.
Free Energy
Energy which is available to do work
Spontaneous Reaction
a reaction which occurs naturally and favors formation of a product under specific conditions. *Key Concept: Spontaneous reactions produce substantial amounts of product and release free energy.
Nonspontaneous reaction
A reaction which does not favor the products under specific conditions
The measure of disorder of a system
Law of Disorder
The natural tendency is for a system to move from an ordered state to to maximum disorder or randomness *Key Concept: an increase in entropy favors the spontaneous chemical reaction, a decrease favors the nonspontaneous reaction.
Gibbs Free-Energy Change
The maximum amount of energy that can be coupled to another process to do useful work. *Key COncept: The numerical value of (delta) G is negative in spontaneous reactions because the system loses free energy.
Rate Law
an expression for the rate of reaction in terms of concentration of reactants.
Specific Rare Constant
(k) for a reaction is proportionally constant relating to concentrations of reaction the the rate of reaction. *Key Concept: the value of specific rate constant is large if the products form quickly and small if they form slowly.*
First Order Reaction
A reaction in which the reaction rate is directly proportional to the concentration of only one reactant.
Elementary Reaction
a reaction in which reactants are converted into products in a single step.
Reaction Mechanism
The series of elementary reactions which take place during a complex reaction. *Key Concept: The peaks correspond to the energies of the activated complex. Each valley corresponds to the energy of an intermediate.* (see figure 18.28)
A product of one of the steps in a reaction mechanism. It then becomes the product for the next step.