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Edexcel International A Level Chemistry

Topic 6
Energetics

Energetics is the study of the heat energy transferred when chemicals react. This topic covers exothermic and endothermic reactions, enthalpy level diagrams, the standard enthalpy change definitions, measuring enthalpy changes by calorimetry, Hess’s law and enthalpy cycles, and bond enthalpies, all examined in Unit 2 and assessed practically through Core Practical 2.

Exam Unit
Unit 2
WCH12/01 – IAS
Specification Points
6.1 – 6.11
11 points covered
Sub-topics
5 pages
Revision notes available
Exam Board
Edexcel IAL
Pearson International

Revision Notes

Exo and endo
Enthalpy
Changes
ΔH, level diagrams, 100 kPa
1

Enthalpy Changes and Standard Conditions

Exothermic and endothermic reactions, enthalpy level diagrams, activation energy and standard conditions.

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Definitions
Standard
Enthalpies
ΔrH, ΔfH, ΔcH, ΔneutH, ΔatH
2

Standard Enthalpy Changes

The five standard enthalpy change definitions and how to write the equation each one refers to.

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q = mcΔT
Calorimetry
solutions, combustion, cooling curves
3

Calorimetry: Measuring Enthalpy Changes

Calculating ΔH from a temperature change, cooling curve corrections, errors and assumptions.

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Enthalpy cycles
Hess’s
Law
formation and combustion routes
4

Hess’s Law and Enthalpy Cycles

Building enthalpy cycles and calculating ΔH from formation and combustion data.

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Break and make
Bond
Enthalpies
mean values and limitations
5

Bond Enthalpies

Mean bond enthalpy, calculating ΔH from bonds broken and made, and why the answers differ from Hess values.

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Specification Coverage

Topic 6 Energetics – Edexcel International A Level Chemistry

The following specification points outline the knowledge and skills students are expected to demonstrate for Topic 6.

6.1
know that:
a
enthalpy change, ΔH, is heat energy change measured at constant pressure
b
standard conditions are 100 kPa and a specified temperature, usually 298 K
6.2
know that, by convention, exothermic reactions have a negative enthalpy change and endothermic reactions have a positive enthalpy change
6.3
be able to construct and interpret enthalpy level diagrams showing an enthalpy change, including appropriate signs for exothermic and endothermic reactions
6.4
know the following definitions of standard enthalpy change:
i
reaction, ΔrH
ii
formation, ΔfH
iii
combustion, ΔcH
iv
neutralisation, ΔneutH
v
atomisation, ΔatH
6.5
be able to use experimental data to calculate:
i
energy transferred in a reaction, recalling and using energy transferred (J) = mass (g) × specific heat capacity (J g⁻¹ °C⁻¹) × temperature change (°C)
ii
the enthalpy change of the reaction in kJ mol⁻¹, for substances mixed in an insulated container and for combustion in a suitable calorimeter
6.6
know Hess’s Law and be able to apply it to:
i
constructing enthalpy cycles
ii
calculating enthalpy changes of reaction using data provided, or data selected from a table or obtained from experiments
6.7
Core Practical 2: determination of the enthalpy change of a reaction using Hess’s Law
6.8
be able to evaluate results obtained from experiments and comment on sources of error, uncertainty and assumptions, including drawing suitable graphs for calorimetry and cooling curve experiments and using cooling curve corrections
6.9
understand the terms ‘bond enthalpy’ and ‘mean bond enthalpy’, use bond enthalpies to calculate enthalpy changes and understand the limitations of doing so
6.10
be able to calculate mean bond enthalpies from enthalpy changes of reaction
6.11
understand that bond enthalpy data gives some indication about which bond will break first in a reaction, how easy or difficult it is and therefore how rapidly a reaction will take place at room temperature
Specification Coverage

Topic 6 Energetics – Edexcel International A Level Chemistry

The following specification points outline the knowledge and skills students are expected to demonstrate for Topic 6.

6.1
know that:
a
enthalpy change, ΔH, is heat energy change measured at constant pressure
b
standard conditions are 100 kPa and a specified temperature, usually 298 K
6.2
know that, by convention, exothermic reactions have a negative enthalpy change and endothermic reactions have a positive enthalpy change
6.3
be able to construct and interpret enthalpy level diagrams showing an enthalpy change, including appropriate signs for exothermic and endothermic reactions
6.4
know the following definitions of standard enthalpy change:
i
reaction, ΔrH
ii
formation, ΔfH
iii
combustion, ΔcH
iv
neutralisation, ΔneutH
v
atomisation, ΔatH
6.5
be able to use experimental data to calculate:
i
energy transferred in a reaction, recalling and using energy transferred (J) = mass (g) × specific heat capacity (J g⁻¹ °C⁻¹) × temperature change (°C)
ii
the enthalpy change of the reaction in kJ mol⁻¹, for substances mixed in an insulated container and for combustion in a suitable calorimeter
6.6
know Hess’s Law and be able to apply it to:
i
constructing enthalpy cycles
ii
calculating enthalpy changes of reaction using data provided, or data selected from a table or obtained from experiments
6.7
Core Practical 2: determination of the enthalpy change of a reaction using Hess’s Law
6.8
be able to evaluate results obtained from experiments and comment on sources of error, uncertainty and assumptions, including drawing suitable graphs for calorimetry and cooling curve experiments and using cooling curve corrections
6.9
understand the terms ‘bond enthalpy’ and ‘mean bond enthalpy’, use bond enthalpies to calculate enthalpy changes and understand the limitations of doing so
6.10
be able to calculate mean bond enthalpies from enthalpy changes of reaction
6.11
understand that bond enthalpy data gives some indication about which bond will break first in a reaction, how easy or difficult it is and therefore how rapidly a reaction will take place at room temperature