Chem 1150 - Chemical Equilibria Lecture Notes

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Equilibria

The Forward reaction is equal to the rate of the reverse reaction (each reaction component is unchanging at equilibrium)

Equilibrium Constant

K = K_eq = (products_eq)/(reactants_eq)

aB + bB <=> cC + dD

K_eq = ([C]^c[D]^d)/([A]^a[B]^b)

Equilibrium Constant Rules:

1. Left hand side will always be K with a specific subscript

2. The right hand side will always be concentration of products over concentration of reactants

3. Balanced reaction coefficients become superscripts

4. Solids and liquids are not included (left out of expression)

5. Expression is always unitless and equal to a numerical value

Equilibrium Constant for Gases

K_p = ([P_C]^C[P_D]^D)/([P_A]^A[P_B]^B)

K_p = (partial pressure of products)^coefficients/(partial pressure of reactants)^coefficients

Use ideal gas law (PV = nRT) to convert between Molar concentrations and Partial Pressure values

Equilibrium Constant Expression Variations

Reverse reaction:
K_rev = 1/K_for

Multiplying a reaction by a factor results in the factor being applied as a power

Reaction Quotient

Ratio of [products]/[reactants]

Q < K → reaction pushes to the right to produce more products

Q > K → reaction pushes to the left to produce more reactants

Le Chatelier’s Principle

An equilibrium put under “stress” will respond in order to alleviate that stress and reestablish equilibrium.

Change in Concentration

If a concentration is decreased, equilibrium will shift to replenish that species

If a concentration is increased, equilibrium will shift to deplete that species

Change in Dilution/Pressure

If pressure is decreased OR solution is diluted, equilibrium will shift to the side that has more mols (gas if pressure problem).

If pressure is increased OR the solution loses volume (evaporation), equilibrium will shift to the side that has fewer mols (gas if pressure problem)



**Liquids & Solids do not count

Change in Heat

If heat is added to the reactants, temperature will shift to the products

If heat is added to the products, temperature will shift to the reactants