equilibrium master

Chemical Equilibrium

A state where the forward and reverse reaction rates are equal and concentrations remain constant.

Equilibrium Expression for aA + bB ⇌ cC + dD

K = \frac{[C]^c[D]^d}{[A]^a[B]^b}

Substances Omitted from Equilibrium Expressions

Pure solids and pure liquids.

Kc vs Kp

Kc uses concentrations (mol/L); Kp uses partial pressures (atm).

Reaction Quotient (Q)

Same as K, but uses initial or current concentrations.

Q < K

The reaction shifts right to form more products.

Q > K

The reaction shifts left to form more reactants.

ICE Table

Used to organize Initial, Change, and Equilibrium concentrations.

Le Châtelier’s Principle

A system at equilibrium shifts to oppose changes in concentration, pressure, or temperature.

Effect of Increasing Reactant Concentration on Equilibrium

Shifts right (toward products).

Effect of Increasing Product Concentration on Equilibrium

Shifts left (toward reactants).

Pressure Change Effect on Gas Equilibrium

Increase in pressure shifts toward fewer gas moles; decrease shifts toward more.

Catalyst Effect on Equilibrium Position

None. It only speeds up reaching equilibrium.

Temperature Effect on Exothermic Reactions

Increasing temperature shifts left (heat is a product).

Temperature Effect on Endothermic Reactions

Increasing temperature shifts right (heat is a reactant).

Kp and Kc Relationship

Kp = Kc(RT)^{\Delta n}

Delta n in Kp = Kc(RT)^{\Delta n}

The change in gas moles: \text{mol products} - \text{mol reactants}.

Gibbs Free Energy and K Relationship

\Delta G^\circ = -RT \ln K

If \Delta G^\circ < 0, what does that say about K?

K > 1; products are favored.

If \Delta G^\circ > 0, what does that say about K?

K < 1; reactants are favored.

Steps to Solve Equilibrium Problem with Unknown Concentrations

Write the equation, set up ICE table, use the K expression, solve for x, calculate concentrations.

Factor that Changes the Value of K

Temperature.

Q = K

The system is already at equilibrium.

Importance of Using Kelvin in Equilibrium Equations

Thermodynamic equations like \Delta G = -RT \ln K require absolute temperature.

Mistake to Avoid in Writing Equilibrium Expressions

Including solids or liquids, or incorrect stoichiometric exponents.