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NSW Syllabuses

Chemistry Stage 6 - Year 12 - Module 5: Equilibrium and Acid Reactions Module 5: Equilibrium and Acid Reactions


A student:

  • CH11/12-4

    selects and processes appropriate qualitative and quantitative data and information using a range of appropriate media

  • CH11/12-5

    analyses and evaluates primary and secondary data and information

  • CH11/12-6

    solves scientific problems using primary and secondary data, critical thinking skills and scientific processes

  • CH11/12-7

    communicates scientific understanding using suitable language and terminology for a specific audience or purpose

  • CH12-12

    explains the characteristics of equilibrium systems, and the factors that affect these systems

Content Focus

Chemical systems may be open or closed. They include physical changes and chemical reactions that can result in observable changes to a system. Students study the effects of changes in temperature, concentration of chemicals and pressure on equilibrium systems, and consider that these can be predicted by applying Le Chatelier’s principle. Students also analyse the quantitative relationship between products and reactants in equilibrium reactions to determine an equilibrium constant. From this calculation, they predict the equilibrium position, either favouring the formation of products or reactants in a chemical reaction.

This module also allows students to understand that scientific knowledge enables scientists to offer valid explanations and make reliable predictions. Students make reliable predictions by comparing equilibrium calculations and equilibrium constants to determine whether a combination of two solutions will result in the formation of a precipitate.

Working Scientifically

In this module, students focus on processing data to determine patterns and trends that enable them to solve problems and communicate scientific understanding of ideas about equilibrium reactions. Students should be provided with opportunities to engage with all the Working Scientifically skills throughout the course.


  • Static and Dynamic Equilibrium

  • Inquiry question: What happens when chemical reactions do not go through to completion?
  • Students:
  • cobalt(II) chloride hydrated and dehydrated
  • iron(III) nitrate and potassium thiocyanate
  • burning magnesium
  • burning steel wool (ACSCH090) ICT
  • model static and dynamic equilibrium and analyse the differences between open and closed systems (ACSCH079, ACSCH091)
  • analyse examples of non-equilibrium systems in terms of the effect of entropy and enthalpy, for example:
  • combustion reactions
  • photosynthesis
  • investigate the relationship between collision theory and reaction rate in order to analyse chemical equilibrium reactions (ACSCH070, ACSCH094) ICT
  • Factors that Affect Equilibrium

  • Inquiry question: What factors affect equilibrium and how?
  • Students:
  • investigate the effects of temperature, concentration, volume and/or pressure on a system at equilibrium and explain how Le Chatelier’s principle can be used to predict such effects, for example:
  • heating cobalt(II) chloride hydrate
  • interaction between nitrogen dioxide and dinitrogen tetroxide
  • iron(III) thiocyanate and varying concentration of ions (ACSCH095)
  • explain the overall observations about equilibrium in terms of the collision theory (ACSCH094)
  • examine how activation energy and heat of reaction affect the position of equilibrium
  • Calculating the Equilibrium Constant (\(K_{eq}\))

  • Inquiry question: How can the position of equilibrium be described and what does the equilibrium constant represent?
  • Students:
  • deduce the equilibrium expression (in terms of \(K_{eq}\)) for homogeneous reactions occurring in solution (ACSCH079, ACSCH096) ICTN
  • perform calculations to find the value of \(K_{eq}\) and concentrations of substances within an equilibrium system, and use these values to make predictions on the direction in which a reaction may proceed (ACSCH096) ICTN
  • qualitatively analyse the effect of temperature on the value of \(K_{eq}\) (ACSCH093) ICTN
  • conduct an investigation to determine \(K_{eq}\) of a chemical equilibrium system, for example:
  • \(K_{eq}\) of the iron(III) thiocyanate equilibrium (ACSCH096) ICT
  • explore the use of \(K_{eq}\) for different types of chemical reactions, including but not limited to:
  • dissociation of ionic solutions
  • dissociation of acids and bases (ACSCH098, ACSCH099)
  • Solution Equilibria

  • Inquiry question: How does solubility relate to chemical equilibrium?
  • Students:
  • describe and analyse the processes involved in the dissolution of ionic compounds in water
  • investigate the use of solubility equilibria by Aboriginal and Torres Strait Islander Peoples when removing toxicity from foods, for example: AHC
  • toxins in cycad fruit
  • conduct an investigation to determine solubility rules, and predict and analyse the composition of substances when two ionic solutions are mixed, for example:
  • potassium chloride and silver nitrate
  • potassium iodide and lead nitrate
  • sodium sulfate and barium nitrate (ACSCH065)
  • derive equilibrium expressions for saturated solutions in terms of \(K_{sp}\) and calculate the solubility of an ionic substance from its \(K_{sp}\) value ICTN
  • predict the formation of a precipitate given the standard reference values for \(K_{sp}\)