1. Equilibrium : A State of Dynamic Balance

2. Reversible Reactions
When a reaction results in complete conversion of reactants to products chemists say it goes to completion
Not all reactions go to completion. They appear to stop because they are reversible
Reversible reactions can occur in both the forward and reverse directions

3. Reversible Reactions cont. . .
Forward N2 + 3H2  2NH3
The reactants are N2 and 3H2; the product is NH3
Reverse N2 + 3H2  2NH3
The reactant is 2NH3; the products are N2 and 3H2
N2 + 3H2 ⇆ 2NH3
The forward and reverse reactions are happening at the same time.

4. Chemical Equilibrium
Chemical equilibrium is a state in which the forward and reverse reactions balance each other because they take place at equal rates.
Rateforward reaction = Ratereverse reaction
This does not mean the concentrations of the products and reactants are the same
Equilibrium is a state of action, not inaction. This process is dynamic; dynamic equilibrium.

5. http://www.youtube.com/watch?v=JsoawKg uU6A

6. Equilibrium Expression and Constant (Keq)
Law of chemical equilibrium states that at a given temperature, a chemical system may reach a state in which a particular ratio of reactant and product concentrations has a constant value known as Keq or equilibrium constant.

7. Equilibrium Constant Keq
Keq is the ratio of product concentrations to reactant concentrations.
Keq only includes compounds that are in the gaseous or aqueous state, not solid or liquid
A large Keq, Keq > 1 means the products are favored over the reactants
A small Keq, Keq < 1 means the reactants are favored over the products

8. Homogenous vs. Heterogeneous Equilibrium
Homogenous equilibrium means all reactants and products are in the same physical state
Ex: H2(g) + O2(g)  H20(g)
Heterogeneous equilibrium is when the reactants and products are in more than one physical state.
Ex: H2O(g) + C(s)  H2(g) + CO(g)

9. Chemical Equilibrium—Keq
aA + bB  cC +dD products [C]c [D]d reactants [A]a [B]b
Keq = =
**only use Keq for gases and aqueous compounds, cross out all liquids and solids

10. Homogenous Equilibria
Given N2(g) + 3H2(g)  2NH3(g) write the equilibrium constant expression for the reaction.

11. Given 2SO2(g) + O2(g)  2SO3(g) write the equilibrium constant expression for the reaction.

12. Heterogeneous Equilibria
Given 2NaHCO3(s)  Na2CO3(s) + CO2(g) + H2O(g) write the equilibrium constant expression for the reaction.
*Products are in the numerator
**Remember not to use solids or liquids in the Keq expression.

13. Calculating the Value of Equilibrium Constants
At equilibrium and 100°C a flask contains: [PCl5]=0.0325M [H2O]=0.025M [HCl]=0.375M [POCl3]=0.250M Calculate the Keq for the reaction PCl5(g) + H20(g)  2HCl(g) + POCl3(g)
**We don’t use units for Keq, or it would get messy!