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In this unit, students learn what determines whether a chemical reaction will occur or not. Material covered includes Exothermic and endothermic reactions, calculation of enthalpy changes, Hess's Law, bond enthalpies, standard enthalpies of reaction. HL students also cover Born-Haber cycle, entropy and spontaneity.

Essential idea

Atomic structure is the unifying concept in Chemistry.

Learning Targets


Global Citizens - Recognition that the use of symbols and equations is an internationally recognized "language".

Topic 5: Energetics (8 hours)

  • Understand and use in context the terms heat, temperature and kinetic energy
  • Define the terms exothermic reaction, endothermic reaction and standard enthalpy change of reaction (ΔHθ)
  • Understand and describe the conditions for standard enthalpy changes and units
  • State that combustion and neutralization are exothermic processes
  • Apply the relationship between temperature change, enthalpy change and the classification of a reaction as endothermic or exothermic
  • Deduce, from an enthalpy level diagram, the relative stabilities of reactants and products, and the sign of the enthalpy change for the reaction
  • Calculate the heat energy change when the temperature of a pure substance is changed
  • Design suitable experimental procedures for measuring the heat energy changes of reactions
  • Calculate the enthalpy change for a reaction using experimental data on temperature changes, quantities of reactants and mass of water. Evaluate the results of experiments to determine enthalpy changes
  • Determine the enthalpy change of a reaction that is the sum of two or three reactions with known enthalpy changes
  • Application of Hess's Law to calculate enthalpy changes of a reaction
  • Define the term average bond enthalpy
  • Explain, in terms of average bond enthalpies, why some reactions are exothermic and others are endothermic
  • Calculate enthalpy changes from known bond enthalpy values and compare to experimentally determined values
  • Sketch, analyse and evaluate potential energy profiles
  • Discuss bond strength in ozone and oxygen and the importance in the atmosphere

Topic 15: Energetics (HL Students only)

  • Define and apply the terms standard state, standard enthalpy change of formation (ΔHfθ) and standard enthalpy change of combustion (ΔHcθ)
  • Determine the enthalpy change of a reaction using standard enthalpy changes of formation and combustion
  • Define and apply the terms lattice enthalpy and electron affinity
  • Explain how the relative sizes and the charges of ions affect the lattice enthalpies of different ionic compounds
  • Construct a Born–Haber cycles and use it to calculate an enthalpy change.
  • Discuss the difference between theoretical and experimental lattice enthalpy values of ionic compounds in terms of their covalent character
  • Explanation of the appropriate steps in the Born - Haber cycle and their representation using appropriate equations
  • Discussion of enthalpy of solution, hydration enthalpy, and lattice enthalpy
  • Perform lab experiments including single replacement reactions in solution
  • State and explain the factors that increase the entropy in a system.
  • Predict whether the entropy change (ΔS) for a given reaction or process is positive or negative
  • Calculate the standard entropy change for a reaction (ΔSθ) using standard entropy values (Sθ).
  • Predict whether a reaction or process will be spontaneous by using the sign of ΔGθ
  • Calculate ΔGθ for a reaction using the equation ΔGθ = ΔHθ - TΔSθ and by using values of the standard free energy change of formation, ΔGfθ
  • Predict the effect of a change in temperature on the spontaneity of a reaction using standard entropy and enthalpy changes and the equation
  • Relate Gibbs free energy change to the position of equilibrium ΔGθ = ΔHθ - TΔSθ.

The detailed curriculum can be consulted here.

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