3.1.4
Energetics
Section 3.1.4 covers the heat energy changes that accompany chemical reactions: exothermic and endothermic reactions, enthalpy change at constant pressure, standard conditions and the standard enthalpies of combustion and formation, calorimetry with q = mcΔT, Hess’s law, and mean bond enthalpies. Required practical 2 measures an enthalpy change directly.
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
AQA A Level Chemistry · 3.1.4 Energetics: Enthalpy changes
The whole section on one A4 page: ΔH and its sign, level diagrams, standard conditions and the standard enthalpy changes.
Calorimetry Map
AQA A Level Chemistry · 3.1.4 Energetics: 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
AQA A Level Chemistry · 3.1.4 Energetics: Hess's law
The whole section on one A4 page: Hess's law, formation and combustion cycles, combining equations, Required Practical 2 and evaluating the result.
Bond Enthalpies Map
AQA A Level Chemistry · 3.1.4 Energetics: 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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3.1.4.1
- ii
know that enthalpy change (DeltaH) is the heat energy change measured under conditions of constant pressure
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3.1.4.2
3.1.4.3
3.1.4.4
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