Unit 1 The Core Principles of Chemistry - 1.4 Energetics

During this topic there will be the opportunity to carry out an internal assessment activity. Please see Appendix 9 for more details.

Students will be assessed on their ability to:

a) demonstrate an understanding of the term enthalpy change, ΔH

b) construct simple enthalpy level diagrams showing the enthalpy change

c) recall the sign of ÄH for exothermic and endothermic reactions, eg illustrated by the use of exo- and endothermic reactions in hot and cold packs

d) recall the definition of standard enthalpy changes of reaction, formation, combustion, neutralization and atomization and use experimental data to calculate energy transferred in a reaction and hence the enthalpy change of the reaction. This will be limited to experiments where substances are mixed in an insulated container, and combustion experiments

e) recall Hess’s Law and apply it to calculating enthalpy changes of reaction from data provided, selected from a table of data or obtained from experiments and understand why standard data is necessary to carry out calculations of this type

f) evaluate the results obtained from experiments using the expression: energy transferred in joules = mass x specific heat capacity x temperature change and comment on sources of error and assumptions made in the experiments. The following types of experiments should be performed:

g) demonstrate an understanding of the terms bond enthalpy and mean bond enthalpy, and use bond enthalpies in Hess cycle calculations and recognise their limitations. 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.