1. What does equilibrium mean?.
Chemical Equilibrium
What does equilibrium mean?.

2. Equilibrium Dynamic state of equilibrium.
State of balance between 2 opposing reactions occurring at the same time and same rate.
In a closed system as products are produced they will react in the reverse reaction until the rates of the forward and reverse reactions are equal. (Rate forward = Rate reverse)
Concentration of reactants and products remain constant.

4. Types of Equilibrium Phase Equilibrium
Rate of one phase change is equal to the rate of the opposing phase change,
Occurs when two phases exist at the same temperature.
Examples:

5. Heating and Cooling Curves

6. Solution Equilibrium
Rate of dissolving = rate of crystallization
Saturated Solution

7. Chemical Equilibrium
Occurs when two or more substances are brought together to yield a chemical reaction and the Rate of forward reaction is equal to the rate of the reverse reaction.
Concentration of reactants and products are constant.

8. Le Chatelier’s Principle
If a stress is applied to a system at equilibrium the equilibrium will shift in the direction that minimizes the stress.
A new point of equilibrium is established with new concentrations of reactants and products.
Stresses include: change in concentration of reactants or products, temperature and pressure.

9. Haber Reaction Equation for the formation of ammonia
N H2 ⇄ 2NH3 + heat

10. Change in concentration
If the concentration of a reactant or product increases you should shift away from the increase.
If the concentration of a reactant or product decreases shift toward the decrease.

11. Practice: N2 + 3H2 ⇄ 2NH3 + heat Stress Shift [N2] [H2] [NH3] Keq
Add N2
Add H2
Add NH3
Remove N2
Remove H2
RemoveNH3

12. Change in Pressure Affects gases only.
An increase in pressure shifts in the direction of the smaller volume of gases diminishing the stress.
A decrease in pressure shifts in the direction of the larger volume of gases diminishing the stress.
If there is no change in the volume of gases involved in the chemical reaction a change in pressure has little affect on the equilibrium.

13. N2(g) + 3H2(g) ⇄ 2NH3(g) + heat
Practice
N2(g) H2(g) ⇄ 2NH3(g) + heat
Stress
Shift
[N2]
[H2]
[NH3]
keq
Increase pressure
Decrease pressure

14. Change in Temperature
An increase in temperature speeds up the rate of both an endothermic and exothermic reaction but unequally.
However an increase in temperature favors the endothermic reaction. (shift away from the heat)
A decrease in temperature favors the exothermic reaction. (shift towards the heat)
Temperature is the only thing that effects the keq. The keq changes in the same direction as the products of the forward reaction.

15. N2(g) + 3H2(g) ⇄ 2NH3(g) + heat
Practice
N2(g) H2(g) ⇄ 2NH3(g) + heat
Stress
Shift
[N2]
[H2]
[NH3]
keq
Increase
temperature
Decrease

16. Effect of a Catalyst
An addition of a catalyst speeds up a reaction by lowering the activation energy and providing an alternate pathway for the reaction.
A catalyst will increase the rate of the forward and reverse reaction equally.
There is no net change in the equilibrium concentrations.
Equilibrium is reached quicker.

17. Equilibrium Constant (Mass action expression)
aA + bB ⇌ cC + dD
Keq = [C]C [D]d /[A]a [B]b
[ ] are the concentrations are equilibrium. Expressed in molarity. (moles/liter)
Only include gases and aqueous ions. Do not include pure solids and liquids they do not affect the keq.
The only stress that changes the keq is a change in temperature.

18. Meaning of keq Keq has no units
Keq > 1 favors the formation of products (forward reaction; ∆G = negative value— spontaneous)
Keq < 1favors the formation of reactants (reverse reaction; ∆G = positive value—not spontaneous)

19. Types of keq
Ksp: solubility product constant (the larger the ksp the more soluble the salt)
Ka: ionizaion constant for an acid(the larger the ka he stronger the acid)
Kb: ionization constant for a base (the larger the kb the stronger the base)
Kw: ionization constant for water (used in ph problems—next unit)