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In this unit, students learn about the factors that affect chemical systems in equilibrium. Material covered includes Dynamic equilibrium and the position of equilibrium, liquid - vapour equilibrium, the equilibrium law.

Essential idea

Many reactions are reversible. These reactions will reach a state of equilibrium when the rates of the forward and reverse reaction are equal. The position of equilibrium can be controlled by changing the conditions.

Learning Targets


Life-Long Learners - Careful observation and recognition of patterns of behavior allows us to make predictions about the behavior of the natural world.

Topic 7: Equilibrium (5 hours)

7.1 Dynamic equilibrium

  • Outline the characteristics of chemical and physical systems in a state of equilibrium.

The position of equilibrium

  • Deduce the equilibrium constant expression (Kc) from the equation for a homogeneous reaction
  • Deduce the extent of a reaction from the magnitude of the equilibrium constant
  • Apply Le Chatelier’s principle to predict the qualitative effects of changes of temperature, pressure and concentration on the position of equilibrium and on the value of the equilibrium constant
  • State and explain the effect of a catalyst on an equilibrium reaction
  • Apply the concepts of kinetics and equilibrium to industrial processes

Topic 17: Equilibrium (HL Students only)

17.1 Liquid–vapour equilibrium

  • Describe the equilibrium established between a liquid and its own vapour and how it is affected by temperature changes
  • Sketch graphs showing the relationship between vapour pressure and temperature and explain them in terms of the kinetic theory
  • State and explain the relationship between enthalpy of vaporization, boiling point and intermolecular forces

16.2 Reaction mechanism

  • Explain that reactions can occur by more than one step and that the slowest step determines the rate of reaction (rate-determining step)
  • Describe the relationship between reaction mechanism, order of reaction and rate-determining step

17.2 The equilibrium law

  • Solve homogeneous equilibrium problems using the expression for Kc

The detailed curriculum can be consulted here.

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