Equilibrium constant

What does the equilibrium constant (Kc) represent

The ratio of product concentrations to reactant concentrations at equilibrium

Write the general equilibrium law expression for aA + bB ⇌ cC + dD

Kc = [C]ᶜ [D]ᵈ / [A]ᵃ [B]ᵇ

What is included in Kc expressions for homogeneous systems

All reactants and products that are gases (g) or aqueous (aq).

How can partial pressure be used in Kc for gaseous systems

Partial pressure is proportional to concentration and can be substituted into the Kc expression for gases.

What is excluded from Kc expressions in heterogeneous systems

Pure solids (s) and liquids (l) are excluded because their concentrations remain constant

What phases are included in heterogeneous Kc expressions

Only gases and aqueous solutions

What does it mean if Kc > 1

The equilibrium favours products and the position shifts to the right

What does it mean if Kc < 1

The equilibrium favours reactants and the position shifts to the left

How is the reverse Kc value related to the forward Kc

Kc(reverse) = 1 / Kc(forward)

How can Kc be used to predict relative amounts of reactants and products

A larger Kc means more products at equilibrium

What does the magnitude of Kc indicate

It shows the extent of the reaction — how far it proceeds towards completion

Why does changing concentration or pressure not affect Kc

Because the ratio of products to reactants adjusts to maintain the constant value of Kc at a fixed temperature

How does Le Châtelier’s principle relate to the equilibrium constant

Temperature change affects the value of K

How does temperature affect the equilibrium constant K

Increasing temperature favours the endothermic direction and changes K; decreasing temperature favours the exothermic direction and changes K

Does changing concentration affect K

No

Does changing pressure affect K

No

Does adding a catalyst affect K

No

Why does temperature change alter K

Because it changes the relative rates of the forward and reverse reactions