Chemguide: Support for CIE A level Chemistry

Learning outcome 5.2

Hess's Law

This statement is about calculating enthalpy changes during a reaction using Hess's Law.

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

Statements 5.2.1 and 5.2.2

You will find an introduction to Hess's Law and simple energy cycles on the Chemguide page Hess's Law and enthalpy change calculations. But this is only an introduction, and you will have to find a source of practice questions such as my chemistry calculations book.

You will find an introduction to bond enthalpy calculations on the Chemguide page bond enthalpy (bond energy).

This bond energy bit is largely a repeat of previous statements. You will probably have recently read this page in statement 5.1.5, where I suggested that you didn't bother with the two Hess's Law cycles until now.

The "use of bond energy data" could also be interpreted in the way previously covered in statement statement 3.4.3(b) and it might be worth looking at that again now.

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© Jim Clark 2019