1. Equilibrium

2. Reversible Reactions Products can reform to make reactants
Completion reaction almost all of the products make reactants
Theoretically all reactions are reversible under the right conditions
The products can re-make the reactants

3. Chemical Equilibrium
The rate of the forward reaction and the rate of the reverse reaction are equal
Concentrations of products and reactants stay the same
Both reactions continue but no net change in the system
H2 + I2 ↔ 2HI
H2 + I2 → 2HI and 2HI → H2 + I2
Both reactions occur at the same rate

5. Many chemical reactions are reversible under ordinary conditions of temperature and concentration.
Reach a state of equilibrium unless at least one of the substances escapes or is removed from the system.

6. products of the forward reaction favored, lies to the right
Higher concentration of products
products of the reverse reaction favored, lies to the left
Higher concentration of reactants
Neither reaction is favored
Considerable concentrations of both reactants and products exist

7. LE CHÂTELIER’S PRINCIPLE
If a system at equilibrium is subjected to a stress, the equilibrium is shifted in the direction that tends to relieve the stress.
So the equilibrium position shifts in the opposite direction of the stress
Changes in pressure, concentration, or temperature can
change the equilibrium position
change the relative amounts of reactants and products

8. Increase reactants equilibrium shifts right to favor products
Increase products, equilibrium shifts left to favor reactants.
If exothermic reaction and add energy, shifts left to favor reactants
If endothermic and add energy, shifts right to favor products

9. Changes in pressure only apply to reactions with gases
If pressure increases, equilibrium shifts to side with the least gas molecules
If pressure decreases, equilibrium shifts to side with the most gas molecules
If the number of molecules is equal on both sides, changing the pressure has no effect.