Chemguide: Support for CIE A level Chemistry

Learning outcome 8.1(g)

This statement is about the relationship between orders of reaction and organic reaction mechanisms

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

Start by reading the page orders of reaction and mechanisms.

You don't specifically need to know about molecularity. Just read that bit of the page quickly so that you can refer back to it in case you come across another source that uses the term.

In the section titled "More about reaction mechanisms and orders of reaction", be sure that you understand how to do problems where the slow step is the first step.

I am not entirely clear what CIE expect in reactions where the slow step isn't the first step. The CIE Chemistry Coursebook passes over this briefly in a very few lines, but with no detailed discussion. It makes no reference to equilibria. And there is no indication from the syllabus or teacher support material that this is wanted.

Note:  The first question CIE set about this in was November 2008, Paper 4, Question 2(b), and was seriously difficult. More recent questions have been more straightforward. The syllabus statements for this topic are much the same as the old syllabus, so you might want to go back through the old questions about it. But ignore the November 2008 question. It was a bad question, which essentially CIE shouldn't have set.

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© Jim Clark 2011 (last modified May 2014)