Calculate equilibrium constants (Kc and Kp) for reversible chemical reactions using concentrations or partial pressures, and convert between the two forms.
Equilibrium Constant
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Converted Constant
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Δn (Change in moles)
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Reaction Direction
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Kc is the equilibrium constant expressed in terms of molar concentrations, while Kp is expressed in terms of partial pressures. Kc is used for reactions in solution, while Kp is used for gas-phase reactions.
Use the relationship Kp = Kc(RT)^Δn, where R is the gas constant (0.0821 L·atm/mol·K), T is temperature in Kelvin, and Δn is the change in moles of gas (products - reactants).
If K > 1, the equilibrium favors products (forward reaction is favored). If K < 1, the equilibrium favors reactants (reverse reaction is favored). K = 1 means equal concentrations of reactants and products.
Stoichiometric coefficients become exponents in the equilibrium expression. For aA + bB ⇌ cC + dD, K = [C]^c[D]^d/[A]^a[B]^b. Larger coefficients increase the impact of that species on the equilibrium.
Only temperature changes the equilibrium constant. Concentration, pressure, and catalysts do not change K, but they can shift the equilibrium position to reach the same K value.
Δn = (sum of coefficients of gaseous products) - (sum of coefficients of gaseous reactants). Count only gas-phase species; exclude solids and liquids from the calculation.