# Topics 5 & 15: Energetics

**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

#### SMEO

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 (
*ΔH*)^{θ} - 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 (
*ΔH*) and standard enthalpy change of combustion (_{f}^{θ}*ΔH*)_{c}^{θ} - 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 (
*ΔS*) using standard entropy values (^{θ}*S*).^{θ} - Predict whether a reaction or process will be spontaneous by using the sign of
*ΔG*^{θ} - Calculate
*ΔG*^{θ }for a reaction using the equation*ΔG*and by using values of the standard free energy change of formation,^{θ}= ΔH^{θ}- TΔS^{θ}*ΔG*_{f}^{θ} - 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
*ΔG*.^{θ}= ΔH^{θ}- TΔS^{θ}

The detailed curriculum can be consulted here.