CIE AS Chemistry (9701) 2019-2021

Revision Notes

1.7.4 Equilibrium Constant

Equilibrium Constant: Concentrations

Equilibrium expression & constant

  • The equilibrium expression is an expression that links the equilibrium constant, Kc, to the concentrations of reactants and products at equilibrium taking the stoichiometry of the equation into account
  • So, for a given reaction:

aA + bB ⇌ cC + dD

the Kc is defined as follows:

Equilibria Equilibrium Expression, downloadable AS & A Level Chemistry revision notes

Equilibrium expression linking the equilibrium concentration of reactants and products at equilibrium

 

  • Solids are ignored in equilibrium expressions
  • The Kc of a reaction is specific and only changes if the temperature of the reaction changes

Worked example: Deducing equilibrium expressions

Equilibria Worked example - Deducing equilibrium expressions, downloadable AS & A Level Chemistry revision notes

Answer

Equilibrium Constant Concentrations Worked Example equations, downloadable AS & A Level Chemistry revision notes

Equilibrium Constant: Partial Pressures

Equilibrium expressions involving partial pressures

  • Equilibrium expressions in terms of partial pressures are written similarly to those involving concentrations with a few differences:

 

Equilibria Comparison Equilibrium Expressions, downloadable AS & A Level Chemistry revision notes

The diagram shows a comparison of writing equilibrium expressions in terms of partial pressures and concentrations

Worked example: Deducing equilibrium expressions of gaseous reactions

Equilibria Worked example - Deducing equilibrium expressions of gaseous reactions, downloadable AS & A Level Chemistry revision notes

Answer

Equilibrium Constant Partial Pressures Worked Example equations, downloadable AS & A Level Chemistry revision notes

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