Equilibrium Constant

The equilibrium constant, K, is a measure of the extent to which a chemical reaction has reached equilibrium.

The equilibrium constant can be defined in terms of molar concentrations (Kc) or partial pressures (Kp).

The value of Kp is generally different from the value of Kc, but they can be related to each other through the ideal gas law.

Questions

• What is the equilibrium constant?
• How is the equilibrium constant defined in terms of molar concentrations?
• How is the equilibrium constant defined in terms of partial pressures?
• How are Kp and Kc related to each other?

Answers

• The equilibrium constant is a measure of the extent to which a chemical reaction has reached equilibrium. It is a ratio of the concentrations of the products to the concentrations of the reactants, at equilibrium.
• The equilibrium constant in terms of molar concentrations (Kc) is defined as:

  “`
  Kc = [C]c[D]d
  [A]a[B]b

  where [A], [B], [C], and [D] are the molar concentrations of the reactants and products, at equilibrium.

• The equilibrium constant in terms of partial pressures (Kp) is defined as:

  Kp =
  �pCH4
  po
  � �pH2O
  po
  �
  �
  pCO
  po
  � �PH2
  po
  �

  where po is the standard pressure (1 atm).

• The value of Kp is generally different from the value of Kc, but they can be related to each other through the ideal gas law. The relationship between Kp and Kc is:

  Kp = Kc (RT)∆n

  where R is the ideal gas constant and ∆n is the difference between the number of moles of gas in the products and the number of moles of gas in the reactants.