Chapter18: Chemical Equilibrium
*Some reactions are reversible.
When these reactions have the same reaction forwards and reverse, the reaction is at equilibrium.

*This does not mean that there are 50/50 mix of products and reactants.

*If Keq = 1, there is an equal concentration of products and reactants.

Equation at Equilibrium

*If Keq>1, there are more products than reactants. The equilibrium "favors" the products.
*If Keq<1, there are more reactants than products. The equilibrium "favors" the reactants.
*Keq equations only include GAS and AQUEOUS compounds. If a compound is solid, do not include it in the equation.

Practice problems:
~2NO2 (g) <=> N2O4(g)
Give the Keq.

~N2 +3H2 <=> 2NH3
Give the Keq.

LeChatelier's Principle (LCP):
If an equilibrium is stressed, the reaction will shift in such a way as to minimize the stress.

Reactants-------------------Products

*If you add more reactants to the equation, then the equation will shift to the right.
*If you add more product to the equation, then the equation will shift to the left.

Pressure Change:
*If pressure is increased, thne the reaction moves to the smaller side (the side with fewer moles).
*If the pressure is decreased, then the reaction moves to the side with more moles.
Example:
~CH3OH <=> 2H2 +CO. Increase the pressure. Which direction does the equation move?
~3O2 <=> 2O3 What happens if you decrease the pressure?

Solubility Product:
NaCl(s) <=> Na+(aq) + Cl- (aq)
Ksp=[Na+][Cl-]
What will happen if CaCl2 is added?
CaCl2 <=> Ca2+ +2Cl-
Cl is the common ion, because it is the ion common between the two equations.

Answers:
~Keq = [N2O4]
[NO2]
~Keq= [NH3]2
[N2][H2]3
~The equation moves to the left.
~The equation will move to the right.

Chapter18: Chemical Equilibrium*Some reactions are reversible.

When these reactions have the same reaction forwards and reverse, the reaction is at equilibrium.

*This does not mean that there are 50/50 mix of products and reactants.

Mass Action ExpressionpA+qB <=> rC+sD

Keq=

[products]=[C]r [D]s[reactants] [B]q [A]p

*If Keq = 1, there is an equal concentration of products and reactants.

*If Keq>1, there are more products than reactants. The equilibrium "favors" the products.

*If Keq<1, there are more reactants than products. The equilibrium "favors" the reactants.

*Keq equations only include GAS and AQUEOUS compounds. If a compound is solid, do not include it in the equation.

Practice problems:

~2NO2 (g) <=> N2O4(g)

Give the Keq.

~N2 +3H2 <=> 2NH3

Give the Keq.

LeChatelier's Principle (LCP):If an equilibrium is stressed, the reaction will shift in such a way as to minimize the stress.

*If you add more product to the equation, then the equation will shift to the left.

Pressure Change:*If pressure is increased, thne the reaction moves to the smaller side (the side with fewer moles).

*If the pressure is decreased, then the reaction moves to the side with more moles.

Example:

~CH3OH <=> 2H2 +CO. Increase the pressure. Which direction does the equation move?

~3O2 <=> 2O3 What happens if you decrease the pressure?

Solubility Product:NaCl(s) <=> Na+(aq) + Cl- (aq)

Ksp=[Na+][Cl-]

What will happen if CaCl2 is added?

CaCl2 <=> Ca2+ +2Cl-

Cl is the common ion, because it is the ion common between the two equations.

Answers:

~Keq =

[N2O4][NO2]

~Keq=

[NH3]2[N2][H2]3

~The equation moves to the left.

~The equation will move to the right.