Chemguide: Support for CIE A level Chemistry

This statement is concerned with definitions and explanations of a whole lot of important terms in chemical energetics.

It is in three parts:

• Part (i) deals with definitions of various enthalpy terms (see below).

• Part (ii) deals with bond enthalpy.

• Part (iii) deals with lattice enthalpy. You will find that this statement is in bold type in the syllabus, which means that it will only be examined at the end of a 2 year course.

Before you go on, you should find and read the statement in your copy of the syllabus.

Part (b)(i)

You will find enthalpy changes of reaction, formation and combustion, together with an explanation of standard conditions and standard states, on the Chemguide page various enthalpy change definitions.

You will find enthalpy changes of hydration and solution on the Chemguide page enthalpies of solution and hydration. Before you look at the calculation part of this page, you first need to have read the page about Hess's Law, which comes up as a part of statement 5(e).

You will find enthalpy change of neutralisation on the Chemguide page enthalpy change of neutralisation.

You will find enthalpy change of atomisation on the Chemguide page lattice enthalpy (lattice energy). Leave that until you do lattice enthalpy in Part (b)(iii) below.

Part (b)(ii)

You will find bond enthalpies on the Chemguide page bond enthalpy (bond energy). This page also includes an introduction to the calculations you will need for statement 5(e)(ii).

Part (b)(iii)

Remember that this won't be examined until the end of a two year course. You will find lattice enthalpies on the Chemguide page lattice enthalpy. CIE want you define lattice enthalpy as the exothermic change from gaseous ions to solid crystal - what I have defined as "lattice formation enthalpy".

This page also includes an introduction to the calculations you will need for statement 5(e)(iv). It would again be better to leave this until you do 5(e). You won't forget - I will direct you back to it again in 5(e)!

You can ignore the section at the end of this page about the formula for magnesium chloride.

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