AQA A Level Chemistry复习笔记5.3.1 Kp Expressions

Kp Expressions

 

  • We have seen previously that equilibrium reactions can be quantified by reference to an equilibrium expression and equilibrium constant
  • The equilibrium expression 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

Kc is defined as follows:

1.7-Equilibria-Equilibrium-Expression

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

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

Gaseous Equilibria

  • This section covers how we manage gases in calculating the equilibrium constant and how an equilibrium yield is affected by the partial pressures of reactants and products
  • Many industrial process involve reactions between gases so this application has important consequences for controlling reaction conditions
  • In the generic example above, if all the substances are gases, we can show the equation with that state symbol

aA (g) + bB (g) ⇌ cC (g) + dD (g)

  • We can write a different equilibrium expression in terms of the partial pressure of the gases
  • This equilibrium constant is called Kp and is defined as follows

5.3.1-Kp-Expressions

 

Equilibrium expression linking the partial pressures of reactants and products at equilibrium

 

  • Solids and liquids are ignored in Kp equilibrium expressions
  • The Kp of a reaction is constant and only changes if the temperature of the reaction changes

Worked Example

Write a Kp expression for the following equilibria and deduce the units of Kp :

  1. N2 (g) + 3H2 (g) ⇌ 2NH3 (g)
  2. 2SO2 (g) + O2 (g) ⇌ 2SO3 (g)

Answer 1

5.3.1-Worked-Example-Answer-1

Answer 2

5.3.1-Worked-Example-Answer-2

转载自savemyexams

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