Applied Science AQA/Enthalpy

Topic TitleEdit

Setting Applied contextEdit

The knowledge of enthalpy changes and the applications of Hess’s Law are important in many areas of scientific research and industry. Biotechnologists develop new fuels such as biodiesel and must compare their energy values with other types of fuel. Development scientists working in the food industry analyse new products for their calorific value and these will also be checked by chemical analysts working for Trading Standards. Chemical engineers in industry will apply Hess’s Law to enable the calculation of enthalpies of reaction in order to determine and better understand the likely effect of reaction conditions on yields.

Syllabus Content What you need to do
•    energy profiles for exothermic and endothermic reactions

•    activation energy using an energy profile

•    types of enthalpy changes from equations (limited to combustion, neutralisation, formation and mean bond enthalpies)

•    units for molar enthalpy change (kJ mol –1)

•    enthalpy changes as the heat energy change (at constant pressure)

•    enthalpy of formation, enthalpy of combustion and enthalpy of reaction, as represented by ∆ f H, ∆cH and ∆rxH

•    the term ‘mean bond enthalpy’

•    calculating enthalpy changes based on Hess’s Law cycles

•    calculating enthalpy changes based on mean bond enthalpies and why these values are only approximate

•    determining practically the molar enthalpy of combustion of a liquid fuel (eg ethanol)

•    determining practically the molar enthalpy of neutralisation for a simple acid–base reaction,


Exploration of key ideas (must be original text, not C&P) – level checked by AQAEdit

In general, point students towards the approach to take, as opposed to just giving them information.

Concept 1Edit

explanation 1

mad scientist

Concept 2Edit

explanation 2

Concept 3Edit

explanation 3

Concept 4Edit

explanation 4

Study TaskEdit

Work to do to understand this topic e.g. research, analysis

Careers and OrganisationsEdit

Carry out some research into these jobs in this area. (Feel free to add other jobs you find.)

Research these roles: What are the benefits of this role to society? What organisations would employ someone in this role? 

(Where would they work?)

What would someone in this role have to do within the organisation? What scientifically-related skills do they need to have? 

What techniques do they need to have mastered?

What experience is needed to undertake this role and its responsibilities within an organisation? What other science personnel will they work with in their organisation.
Job 1
Job 2

Relevant practical/sEdit

– relating to criteria skills

Quick questionsEdit


quick questions


click to reveal answer

Exam-style questionsEdit

– can we use old AQA qs… e.g. from more than 5 years ago? With Examiner comments


click to reveal answer


to other sections within this book

to good external websites (including AQA website, wikipedia, relevant applications / companies) - also considering links in spec

References / BibliographyEdit

of recommended text books

including mapped refs to existing books

Back to Contents