Chemical Equilibrium Dr. Walker

What will you learn? Reactions can occur in two directions simultaneously. LeChatelier’s Principle indicates which way the reaction will shift with a change in temperature, pressure, or concentration.

Reversible Reactions 2 HgO(s)  2Hg(l) + O2(g) Defined A chemical reaction in which the products can react to re-form the reactants Usually represented by a double sided arrow Equilibrium can be to the left or the right depending on conditions 2 HgO(s)  2Hg(l) + O2(g)

Dynamic Equilibrium Reactions continue to take place Reactant molecules continue to be converted to product (forward reaction) Product continues to be converted to reactant (reverse reaction) Forward and reverse reactions take place at the same rate at equilibrium Reactants become products 2 HgO(s)  2Hg(l) + O2(g) Products become Reactants

Write all Chemical Equilibrium When forward and reverse reactions take place at the same rate No overall change in the actual amount present in the reaction Does not imply equal concentrations of reactants and products, only constant concentrations

Write all

Le Chatelier’s Principle Write bold Le Chatelier’s Principle “If a stress is applied to a system in dynamic equilibrium, the system changes to relieve the stress.” Chemical reactions try to balance out what they perceive to be normal. Stresses that upset the equilibrium of a chemical system Concentrations of reactants and products Temperature Pressure

Concentration and Le Chatelier’s Principle Write bold Concentration and Le Chatelier’s Principle Changes in concentration disturb the equilibrium, so the system adapts to minimize the effects of the disturbance System changes to use up the “excess” reactant If you add something to one side, the equilibrium moves in the opposite direction

An Example

An Example

Temperature and LeChatelier Exothermic Reaction Energy is a product Increase Temperature: Favors Reactants Endothermic Reaction Energy is a reactant Increase Temperature: Favors Product

LeChatelier Example #1 A closed container of ice and water is at equilibrium. Then, the temperature is raised. Ice + Energy  Water right The system temporarily shifts to the _______ to restore equilibrium.

LeChatelier Example #2 A closed container of N2O4 and NO2 is at equilibrium. NO2 is added to the container. N2O4 (g) + Energy  2 NO2 (g) The system temporarily shifts to the _______ to restore equilibrium. left

LeChatelier Example #3 A closed container of water and its vapor is at equilibrium. Vapor is removed from the system. water + Energy  vapor right The system temporarily shifts to the _______ to restore equilibrium.

A Real World Example

A Real World Example

Pressure and LeChatelier Write bold Pressure and LeChatelier 3 H2(g) + N2(g) 2 NH3(g) As pressure increases, the number of moles of product increases Think of it as adding to the side with more moles Shifts towards side with fewer moles Particles are forced to come closer together, therefore reacting the reactants to form more products

Answer!