Topic 8
Energetics I
Topic 8 introduces the heat energy changes that accompany chemical reactions. It covers exothermic and endothermic reactions, enthalpy level diagrams and reaction profiles, standard conditions and the standard enthalpy change definitions, measuring enthalpy changes by calorimetry, Hess’s law and enthalpy cycles, and mean bond enthalpies. The practical side is assessed in Core Practical 8.
Revision Notes
5 revision notes, in the order the specification teaches them.
Enthalpy Changes and Standard Conditions
Exothermic and endothermic reactions, enthalpy level diagrams, activation energy and standard conditions.
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Standard Enthalpy Changes
The standard enthalpy change definitions and the equation each one refers to.
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Calorimetry: Measuring Enthalpy Changes
Calculating ΔH from a temperature change, cooling curve corrections, errors and assumptions.
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Hess’s Law and Enthalpy Cycles
Building enthalpy cycles and calculating ΔH from formation and combustion data.
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Bond Enthalpies
Mean bond enthalpy, calculating ΔH from bonds broken and made, and why the answers differ from Hess values.
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Enthalpy Changes Map
Edexcel A Level Chemistry · Topic 8 Enthalpy Changes
The whole section on one A4 page: ΔH and its sign, diagrams and Eₐ, standard conditions and the standard enthalpy changes.
Calorimetry Map
Edexcel A Level Chemistry · Topic 8 Calorimetry
The whole section on one A4 page: q = mcΔT, reactions in solution, burning fuels, errors and assumptions, uncertainty and the cooling-curve correction.
Hess's Law Map
Edexcel A Level Chemistry · Topic 8 Hess's Law
The whole section on one A4 page: Hess's law, formation and combustion cycles, combining equations, Core Practical 8 and evaluating the result.
Bond Enthalpies Map
Edexcel A Level Chemistry · Topic 8 Bond Enthalpies
The whole section on one A4 page: bond enthalpy, mean bond enthalpy, ΔH from bonds broken and made, working back, limitations and which bond breaks first.
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Specification
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Self-assessment · 22 points
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8.1
8.2
8.3
8.4
8.5
- i
understand experiments to measure enthalpy changes in terms of: processing results using the expression: energy transferred = mass x specific heat capacity × temperature change (Q=mcΔT)
Revise - ii
understand experiments to measure enthalpy changes in terms of: evaluating sources of error and assumptions made in the experiments Students will need to consider experiments where: o substances are mixed in an insulated container and the temperature change is measured o enthalpy of combustion is measured, such as using a series of alcohols in a spirit burner o the enthalpy change cannot be measured directly.
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8.6
- 8.6
be able to calculate enthalpy changes in kJ mol-1 from given experimental results Both a sign and units are expected in the final answer.
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8.7
8.8
8.9
8.10
8.11
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