Topic 8 – Energetics I
In order to develop their practical skills, students should be encouraged to carry out a range of practical experiments related to this topic. Possible
experiments include a wide variety of calorimetry experiments involving displacement and neutralisation reactions, investigating the enthalpy of
combustion of a homologous series of alcohols. Mathematical skills that could be developed in this topic include plotting and extrapolating graphs of
temperature rise against time for displacement reactions, calculating enthalpy changes in J and in kJ mol -1, using algebra to solve Hess’s law
problems, calculating enthalpy changes using bond enthalpies. Within this topic, students can consider how the use of Hess’s Law can facilitate the
study of energy changes in reactions which are not directly measurable. They can also consider the value of a general chemical concept, such as
mean bond enthalpy, and why the use of a simplification such as this has some benefits, as well as some short-comings.
1. know that standard conditions are…
What are standard conditions defined as?
Standard conditions are 100kPa and a stated temperature, generally 298K.
2. know the definition of enthalpy change
Define enthalpy change.
Enthalpy change is the heat energy change measured at a constant pressure.
3. be able to construct and interpret enthalpy level diagrams showing an enthalpy change, including
appropriate signs for exothermic and endothermic reactions
Activation energy is not shown in enthalpy level diagrams but it is shown in reaction profile diagrams.
1 - Enthalpy Level Diagram 2 - Reaction Profile Diagram(s)
4. be able to define standard enthalpy change of:
i reaction
Define ‘standard enthalpy change of reaction’.
The enthalpy change in a reaction under standard conditions of 100kPa and a stated temperature
between the number of moles of reactants shown in the equation.
ii formation
Define ‘standard enthalpy change of formation’.
The enthalpy change when one mole of a substance is formed from its elements under standard
conditions of 100kPa and a stated temperature with all substances in their standard states.
In order to develop their practical skills, students should be encouraged to carry out a range of practical experiments related to this topic. Possible
experiments include a wide variety of calorimetry experiments involving displacement and neutralisation reactions, investigating the enthalpy of
combustion of a homologous series of alcohols. Mathematical skills that could be developed in this topic include plotting and extrapolating graphs of
temperature rise against time for displacement reactions, calculating enthalpy changes in J and in kJ mol -1, using algebra to solve Hess’s law
problems, calculating enthalpy changes using bond enthalpies. Within this topic, students can consider how the use of Hess’s Law can facilitate the
study of energy changes in reactions which are not directly measurable. They can also consider the value of a general chemical concept, such as
mean bond enthalpy, and why the use of a simplification such as this has some benefits, as well as some short-comings.
1. know that standard conditions are…
What are standard conditions defined as?
Standard conditions are 100kPa and a stated temperature, generally 298K.
2. know the definition of enthalpy change
Define enthalpy change.
Enthalpy change is the heat energy change measured at a constant pressure.
3. be able to construct and interpret enthalpy level diagrams showing an enthalpy change, including
appropriate signs for exothermic and endothermic reactions
Activation energy is not shown in enthalpy level diagrams but it is shown in reaction profile diagrams.
1 - Enthalpy Level Diagram 2 - Reaction Profile Diagram(s)
4. be able to define standard enthalpy change of:
i reaction
Define ‘standard enthalpy change of reaction’.
The enthalpy change in a reaction under standard conditions of 100kPa and a stated temperature
between the number of moles of reactants shown in the equation.
ii formation
Define ‘standard enthalpy change of formation’.
The enthalpy change when one mole of a substance is formed from its elements under standard
conditions of 100kPa and a stated temperature with all substances in their standard states.
