#3.2.1a
explanation that some chemical reactions are accompanied by enthalpy changes that are exothermic (∆H, negative) or endothermic (∆H, positive)
#3.2.1b
construction of enthalpy profile diagrams to show the difference in the enthalpy of reactants compared with products
#3.2.1c
qualitative explanation of the term activation energy, including use of enthalpy profile diagrams
Activation energy in terms of the minimum energy required for a reaction to take place.
#3.2.1d
explanation and use of the terms:
(i) standard conditions and standard states (physical states under standard conditions)
(ii) enthalpy change of reaction (enthalpy change associated with a stated equation, ∆rH)
(iii) enthalpy change of formation (formation of 1 mol of a compound from its elements, ∆fH)
(iv) enthalpy change of combustion (complete combustion of 1 mol of a substance, ∆cH)
(v) enthalpy change of neutralisation (formation of 1 mol of water from neutralisation, ∆neutH)
Definitions required for enthalpy changes of formation, combustion and neutralisation only.
Standard conditions can be considered as 100 kPa and a stated temperature, 298 K.
#3.2.1e
determination of enthalpy changes directly from appropriate experimental results, including use of the relationship: \(q = mc∆T\)
PAG3
#3.2.1f
(i) explanation of the term average bond enthalpy (breaking of 1 mol of bonds in gaseous molecules)
(ii) explanation of exothermic and endothermic reactions in terms of enthalpy changes associated with the breaking and making of chemical bonds
(iii) use of average bond enthalpies to calculate enthalpy changes and related quantities (see also 2.2.2f)
Definition of average bond enthalpy not required.
Learners are expected to understand that an actual bond enthalpy may differ from the average value.
#3.2.1g
Hess’ law for construction of enthalpy cycles and calculations to determine indirectly:
(i) an enthalpy change of reaction from enthalpy changes of combustion
(ii) an enthalpy change of reaction from enthalpy changes of formation
(iii) enthalpy changes from unfamiliar enthalpy cycles
Definition of Hess’ law not required.
Unfamiliar enthalpy cycles will be provided.
#3.2.1h
the techniques and procedures used to determine enthalpy changes directly and indirectly.
To include the enthalpy changes covered in 5.2.1c.
PAG3