Introduction to Equilibrium Lesson Outline The CollisonReaction Theory

Introduction to Equilibrium

Lesson Outline The Collison-Reaction Theory Equilibrium Types of Equilibrium Describing Equilibrium Classes of Chemical Equilibria

Collison-Reaction Theory Effective collisions occur when reactants collide. Products can also collide to form reactants

Equilibrium The State of a closed system with no observable changes (macroscopic properties) occurring. Changes that can be observed and measure (concentration, p. H, Temperature) Dynamic Equilibrium is a balance between two opposite process occurring at the same rate

Establishing Equilibrium The forward and reverse reactions will initially proceed at different rates (depending on different concentrations) with only reactants, the forward reaction will initially be faster as it is the only reaction possible As products form, the forward reaction will slow down and the reverse reaction will speed up. Eventually the rates of the forward and reverse reactions will become equal.

Types of Equilibrium Phase Equilibrium involves a single chemical substance existing in more then one phase. Water in a sealed jar Solubility Equilibrium involves a single chemical solute interacting with a solvent at saturation. Excess salt dissolved in water Chemical Reaction Equilibrium involves several substances (reactants and products) in a reaction.

The Hydrogen-Iodine Reaction System

Describing Equilibrium Constant – all substances of the same reaction Percent Reaction (% yield) – Equilibrium for one substance in the reaction the yield of product measured at Eq compared to the maximum possible yield of product (max yield of product calculated using stoichiometry)

Classes of Chemical Equilibria Type of Equilibria % Yield Non-spontaneous (no apparent reaction) Negligible (<1%) Reactants favored Products favored Quantitative (complete) <50% >99% Position of Eq. no evidence of reaction <50% � at eq. there will be more reactants than products >50% � at eq. there will be more products than reactants (reverse rxn is negligible) not really equilibrium use regular stoichiometry

Looking Forward Le Chatelier‘s Principle