Wednesday, April 9, 2008 Reminder – Lab Report Due Friday Homework – Reading Analysis (Sections Questions about Lab Section 17.2 Notes Section 17.3 Notes

Types of Reactions Homogeneous Reaction – Reactions involving reactants and products in the same state. Heterogeneous Reactions – Reactions involving reactants and products in different states

Equilibrium Equilibrium – The exact balance of two processes, one of which is opposite of the other Chemical Equilibrium – dynamic state where the concentrations of all reactants and products remain constant

H 2 O(g) + CO(g)  H 2 (g) + CO 2 (g) A.Equal number of moles of water and carbon monoxide are mixed in a closed container B.The reaction begins. Some products, hydrogen and carbon dioxide are formed C.Reaction continues, more reactants are changed to products D.Time passes, numbers of reactants and products remain the same as C. Equilibrium is reached

Changes with time in the rates of reactions.

Equilibrium Equilibrium Position – a particular set of equilibrium concentrations of all reactants and products in a chemical system.

The Equilibrium Constant aA + bB  cC + dD  Represents a chemical reaction  A,B,C,D are chemical reactants and products and a,b,c,d are coefficients Equilibrium Expression

The Equilibrium Constant  The square brackets indicate the concentration of the chemical species at equilibrium (mol/L)  K is called the equilibrium constant  The position of a heterogeneous equilibrium does not depend on the amounts of pure solids or liquids present  The concentrations of pure solids and pure liquids involved in a chemical reaction are not included in the equilibrium expression for the reaction

Practice Problem – Page 606 Write the equilibrium expression for the following reactions: a. H 2(g) + F 2(g) ↔ 2HF (g) b. N 2(g) + 3H 2(g) ↔ 2NH 3(g)

Equilibrium Le Chatelier’s Principle – if stress is applied to a system at equilibrium, the system changes to relieve the stress. 1. Concentration 2. Temperature 2SO 2 (g) + O 2 (g)  2SO 3 (g) + heat 3. Pressure

N 2 (g) + 3H 2 (g)  2NH 3 (g) + E Concentration of reactants and products  When a product or reactant is added to a system at equilibrium, the system shifts away from the added component.  If a reactant or product is removed, the sytem shifts toward the removed component Temperature  Endothermic reactions – energy is treated as a reactant  Exothermic reactions – energy is treated as a product

CH 4(g) + O 2(g) ↔ CO 2(g) + H 2 O (l) Predict the effect of the following: 1. Removal of water 2. Addition of CO 2 3. Heat 4. Cold 5. Addition of CH 4 1. No effect; 2. Shift right; 3. Shift right; 4. Shift left; 5. Shift right