**Homogeneous Equilibria for Gaseous Reactions**

For gas-phase reactions, the equilibrium constant may be expressed in terms of either the molar concentrations (*K*_{c}) or partial pressures (*K*_{p}) of the reactants and products. A relation between these two *K* values may be simply derived from the ideal gas equation and the definition of molarity. According to the ideal gas equation:

Molar concentration or molarity is given by number of moles divided by the volume:

Thus,

where *P* is partial pressure, *V* is volume, *n* is number of moles, *R* is the gas constant, *T* is temperature, and *M* is molar concentration.

For the gas-phase reaction: *m *A + *n *B ⇌ *x *C + *y *D

And so, the relationship between *K*_{c} and *K*_{P} is

where Δ*n* is the difference in the molar amounts of product and reactant gases, in this case:

*This text has been adapted from **Openstax, Chemistry 2e, Section 13.2 Equilibrium Constants*.

ABOUT JoVE

Copyright © 2024 MyJoVE Corporation. All rights reserved