5.1.2 (a) Use of the terms Mole Fraction and Partial Pressure

Syllabus

(a) use of the terms mole fraction and partial pressure

What does this mean?

Partial Pressures

If you mix Sulphur Dioxide and Oxygen some Sulphur Trioxide will form and the mixture will settle into an equilibrium containing all three gases.

SO_2(g) + O_2(g) ⇌ SO_3(g)

If you then measured the pressure in the reaction vessel you would be combining the pressure exerted by the SO₂, the O₂, and the SO₃.

Partial Pressure is the term used for the pressure each gas would exert if it occupied the entire vessel entirely on its own at the same temperature.

So the sum of the partial pressures of all the gases in the vessel should equal the total pressure in the vessel.

p_{(SO2) +} p_{(O2) +} p_{(SO3) =} p_Total

Mole Fraction.

In this mixture of gases there will be a measurable number of moles of SO₂, O₂, and SO₃.