Wednesday, April 9, 2008

Reminder – Lab Report Due Friday Homework – Reading Analysis (Sections

17.2-17.3 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

H2O(g) + CO(g) H2(g) + CO2(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 productsD. 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 + dDRepresents a chemical reactionA,B,C,D are chemical reactants and products

and a,b,c,d are coefficients

Equilibrium Expression

ba

dc

BADC

K

The Equilibrium Constant ba

dc

BADC

K

The square brackets indicate the concentration of the chemical species at equilibrium (mol/L)K is called the equilibrium constantThe position of a heterogeneous equilibrium does not depend on the amounts of pure solids or liquids presentThe 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. H2(g) + F2(g) ↔ 2HF(g)

b. N2(g) + 3H2(g) ↔ 2NH3(g)

22

2

FHHF

K

3

22

2

3

HNNH

K

EquilibriumLe Chatelier’s Principle – if stress is

applied to a system at equilibrium, the system changes to relieve the stress.

1. Concentration

2. Temperature2SO2(g) + O2(g) 2SO3(g) + heat

3. Pressure

N2(g) + 3H2(g) 2NH3(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

CH4(g) + O2(g) ↔ CO2(g) + H2O(l)

Predict the effect of the following:1. Removal of water

2. Addition of CO2

3. Heat4. Cold

5. Addition of CH4

1. No effect; 2. Shift right; 3. Shift right; 4. Shift left; 5. Shift right