Equilibrium Constant for Homogeneous Reactions (Kc)
Formulating and calculating the equilibrium constant in terms of molar concentrations for reactions in a single phase.
What is Equilibrium Constant for Homogeneous Reactions (Kc)?
A chemical reaction in which all reactants and products are in the same physical phase (e.g., all gaseous or all aqueous).
Key formula / rule: Equilibrium Constant (Kc)
Key points
- Define the equilibrium constant Kc.
- Write the expression for Kc for a given homogeneous reaction.
- Interpret the meaning of Kc value.
- Calculate Kc from equilibrium concentrations.
Common exam trap
Including concentrations of pure solids or liquids in the Kc expression.
Definitions
- Term
Homogeneous Reaction
- Meaning
A chemical reaction in which all reactants and products are in the same physical phase (e.g., all gaseous or all aqueous).
- Term
Equilibrium Constant (Kc)
- Meaning
The ratio of the product of molar concentrations of products to the product of molar concentrations of reactants, each raised to the power of their stoichiometric coefficient, at equilibrium for a homogeneous reaction at a specific temperature.
Learning objectives
Define the equilibrium constant Kc.
Write the expression for Kc for a given homogeneous reaction.
Interpret the meaning of Kc value.
Calculate Kc from equilibrium concentrations.
Formulae
- Name
Equilibrium Constant (Kc)
- Note
For a homogeneous reaction aA + bB ⇌ cC + dD, where [X] is the molar concentration of species X at equilibrium.
- Expression
Kc = ([C]c [D]d) / ([A]a [B]b)
Prerequisites
Understanding of reversible reactions.
Concept of chemical equilibrium.
Molar concentration calculations.
Stoichiometry of chemical reactions.
Common mistakes
Including concentrations of pure solids or liquids in the Kc expression.
Incorrectly using initial concentrations instead of equilibrium concentrations.
Forgetting to raise concentrations to their stoichiometric coefficients.
Confusing Kc with Kp or other equilibrium constants.
Keywords
Equilibrium Constant
Kc
Homogeneous Reaction
Molar Concentration
Chemical Equilibrium
Reversible Reaction
Stoichiometric Coefficient
Practice preview
For the reaction PCl5(g) <=> PCl3(g) + Cl2(g), the value of Kc is 1.8 x 10^-2 at 500 K. If at equilibrium, the partial pressures of PCl3 and Cl2 are 0.2 atm each, what is the partial pressure of PCl5?…
medium
Consider the reaction: H2(g) + I2(g) <=> 2HI(g). At equilibrium, if the concentrations of H2, I2, and HI are 0.1 M, 0.2 M, and 0.8 M respectively, what is the value of Kc?…
medium
For the reversible reaction, N2(g) + 3H2(g) <=> 2NH3(g), the expression for the equilibrium constant Kc is:…
easy