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14.3 : Homogeneous Equilibria for Gaseous Reactions

Homogeneous Equilibria for Gaseous Reactions

For gas-phase reactions, the equilibrium constant may be expressed in terms of either the molar concentrations (Kc) or partial pressures (Kp) 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:

Chemical equilibrium; acetic acid ionization; equation HA ⇌ H⁺ + A⁻; reaction dynamics diagram.

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

DNA cloning process; plasmid insertion. Genetic diagram for educational research.

Thus,

Static equilibrium concept; ΣF=0, torque balance MA=0; force diagram with vectors, moments.

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

Chemical reaction mechanism; diagram of an electrophilic aromatic substitution; shows reactants to products.

And so, the relationship between Kc and KP is

Static equilibrium formulas, ΣFx=0, ΣFy=0, MA=0, diagram with force vectors for study analysis.

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

Static equilibrium diagram; ΣFx=0, ΣFy=0; beam balance analysis; physics education resource.

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

Tags

Homogeneous EquilibriaGaseous ReactionsEquilibrium ConstantPartial PressuresMolar ConcentrationsReversible ReactionStoichiometric CoefficientsKpKcIdeal Gas EquationMolarityIndividual Partial PressuresMolar Concentration EquivalentModified Expression

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