1. Equilibrium

2. • A state of rate balance between two
opposing changes
• types of equilibrium
1. reaction equilibrium--rate of synthesis = rate of decomposition
2. solution equilibrium(takes place in a saturated solution)--rate of
dissolving = rate of precipitating
3. phase equilibrium--rate of melting =rate of freezing (at the freezing
point) or rate of boiling = rate of condensing (at boiling point)

3. properties of a system at equilibrium
• 1. since equilibrium is a rate balance, anything that might change reaction rate
must be kept out of the system or the eq will be ruined.The system must be
closed.
1. temp and pressure
2. don’t change the conc.--no more reactant, don’t let any product
escape
• 2. A system at equilibrium with stay that way forever
• 3. Equilibrium is dynamic (its always in motion)
• 4. delta G at equilibrium = Zero

4. stressing the equilibrium
Le Chatelier’s Principle
• Factors affecting equilibrium
• Predicting the direction of the shift
• Predicting resulting change in concentration
• Making equilibrium serve your own evil
purposes

5. Factors Affecting Equilibrium
• Equilibrium is a rate balance
• anything that affects one of the reactions
can throw the equilibrium off
1.
2.
3.
4.
5.

6. Using Le Chatelier
• Stress--add or remove a reactant.Add or remove a
product
• Shift-- the reaction will shift away from what is
added and towards what is being removed
• Change in conc. the conc. of what is being shifted
toward increases.The conc. of what is being shifted
away from decreases

7. concentration• If a reactant is added:
1. the number of collisions between reactant particles increases
2. the rate of the forward reaction increases (forward shift)
N2 + 3H2 <--> 2NH3 + heat
• If a product is added:
1. the number of collisions between product particles increases
2. the rate of the reverse reaction increases (reverse shift)
N2 + 3H2 <--> 2NH3 + heat
Stress--Shift--Change in Conc.

8. concentration
• If a reactant is removed:
1. the number of collisions between reactant particles decreases
2. the rate of the forward reaction decreases (reverse shift)
N2 + 3H2 <--> 2NH3 + heat
• If a product is removed:
1. the number of collisions between product particles decreases
2. the rate of the reverse reaction decreases (forward shift)
N2 + 3H2 <--> 2NH3 + heat
Stress--Shift--Change in Conc.

9. temp and EQ
• If temp is increased
1. the eq will shift in the endothermic direction (converting the excess KE to PE
2. the endothermic direction is away from the side with the heat (kJ)
N2 + 3H2 <--> 2NH3 + heat
• If temperature is decreased
1. the equilibrium will shift in the exothermic direction (releasing PE to make up
for the lost KE)
2.The exothermic direction is towards the side with the heat
N2 + 3H2 <--> 2NH3 + heat

10. pressure and EQ
• If pressure is increased
1. the eq will shift to the side with the fewer moles of gas to bring the pressure
down
N2(g) + 3H2(g) <--> 2NH3(g) + heat
• If pressure is decreased
1. the equilibrium will shift toward the side with more moles of gas to bring the
pressure back up
N2(g) + 3H2(g) <--> 2NH3(g) + heat