Chemguide: Support for CIE A level Chemistry


Learning outcome 7.1(e)

This statement deals with calculating values for Kc and Kp from given data.

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


Obviously, before you can do this, you need to be confident about writing expressions for equilibrium constants as covered in statement 7.1(d). If you can't do that, go back and look at it again.

If you are given the values for all of the concentrations or partial pressures, then this is simply a matter of slotting the numbers into the right equilibrium constant expression. But you also have to work out what the units are.

Unfortunately, it is more likely that you won't be given all the numbers that you need, and will have to calculate one or more of them. This isn't actually very difficult, but there are so many different variations on this, that it is impossible to give them all on this page.

My chemistry calculations book has no fewer than 14 pages looking at finding values for Kc and Kp including their units. I can't repeat this here.

CIE's Chemistry Coursebook has 9 clearly worked examples, together with end-of-chapter questions where the answers are given on the CD-ROM.

Calculations are much better learnt from books than on the web.


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© Jim Clark 2011 (last modified April 2014)