Chemguide: Support for CIE A level Chemistry

Learning outcome 4.1

The gaseous state: ideal and real gases and pV = nRT

This statement deals with the origin of pressure in gases, with the concept of ideal gases, and with the ideal gas equation. Before you go on, you should find and read the statements in your copy of the syllabus.

Statements 4.1.1, 4.1.2 and 4.1.3

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

Ideal gases

You will need to read the whole of the page about ideal gases.

In statement 4.1.3, you will need more practice in using the ideal gas equation than you will find on that page. Because this topic is covered in my chemistry calculations book (see pages 48 to 51, and end-of-chapter problems 20 - 23), I can't go any further than this with online help.

For reasons that I have explained on another page, all I can do in these cases is to refer you to the book. Or, of course, you can find an alternative source of calculations. But it is essential that you practice doing these ideal gas equation sums.

Real gases

Real gases aren't specifically mentioned by the syllabus, but CIE will expect you to know something about them so that you can see where the assumptions made about an ideal gas are faulty.

Real gases are covered in much more detail than you will need on this Chemguide page.

In order to understand the topic properly, you need to read the whole of this page apart from the section about the van der Waals equation. You won't, however, be expected to remember anything specifically about compression factors.

You will, however, be expected to know why ideal gases differ from real gases in terms of the intermolecular forces, and the space taken up by the molecules.

You will also be expected to know that gases become less ideal at low temperatures and very high pressures, and why that is so.

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© Jim Clark 2019