Equilibrium Constant (Kc/Kp) Calculator

Equilibrium Constant (Kc/Kp) Calculator

Reactants (Equilibrium Concentration)

Products (Equilibrium Concentration)

Chemical Equilibrium & The Equilibrium Constant

Chemical equilibrium is the state reached in a reversible chemical reaction where the rate of the forward reaction equals the rate of the reverse reaction. At equilibrium, the concentrations (or partial pressures) of reactants and products remain constant over time, even though the forward and reverse reactions are still occurring.

The Equilibrium Constant (K) is a value that quantifies the relative amounts of products and reactants present at equilibrium. It indicates the extent to which a reaction proceeds before reaching equilibrium.

  • Kc is the equilibrium constant expressed in terms of molar concentrations ([M]).
  • Kp is the equilibrium constant expressed in terms of partial pressures (usually in atm).

The relationship between them is given by Kp = Kc(RT)Δn, where Δn is the change in the moles of gas between products and reactants.

Frequently Asked Questions

What does a large K value mean?

A large equilibrium constant (K >> 1) means that at equilibrium, the concentration (or pressure) of the products is significantly higher than that of the reactants. This indicates that the reaction strongly favors the formation of products; the equilibrium "lies to the right." Conversely, a small K value (K << 1) means the reactants are favored, and the equilibrium "lies to the left."

Do solids and pure liquids affect Kc or Kp?

No. The concentrations (or activities) of pure solids and pure liquids are considered constant and do not change significantly during a reaction. Therefore, they are omitted from the equilibrium constant expression. Only gases (for Kp and Kc) and aqueous species (for Kc) are included.

What is Δn in the Kp/Kc conversion?

Δn (delta n) is the change in the number of moles of gas during the reaction. It is calculated as:
Δn = (Total moles of gaseous products) - (Total moles of gaseous reactants)
You find these moles by summing the stoichiometric coefficients of only the gaseous species on each side of the balanced equation.

What is the value of R used in the conversion?

The ideal gas constant R used in the Kp = Kc(RT)Δn conversion typically uses units consistent with pressure in atmospheres (atm) and volume in Liters (L). The value used in this calculator is R = 0.08206 L·atm/(mol·K). Temperature (T) must always be in Kelvin (K).