IB Chemistry - Stoichiometry

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Robert Boyle investigated the relationship between the volume of a fixed mass of gas and its pressure under conditions of constant temperature.

Syllabus reference

Structure 1.5.3 - The molar volume of an ideal gas is a constant at a specific temperature and pressure.

  • Investigate the relationship between temperature, pressure and volume for a fixed mass of an ideal gas and analyse graphs relating these variables.

Guidance

  • The names of specific gas laws will not be assessed.
  • The value for the molar volume of an ideal gas under standard temperature and pressure (STP) is given in the data booklet.

Tools and links

  • Nature of science, Tool 2 and Tool 3, Reactivity 2.2 - Graphs can be presented as sketches or as accurately plotted data points.
  • What are the advantages and limitations of each representation?

Boyle's law

Robert Boyle found that for a given number of moles of gas the volume of the gas is proportional to its pressure provided the temperature is kept constant.

This can be expressed as:

PV = constant

The pressure of a gas derived from collisions of the gas particles with the walls of the container. If the volume is decreased then the gas particles are resticted to less space and there are more collisions per second at the walls and consequently a greater pressure is exerted.

Boyles law allows calculation of new volume and/or pressure conditions (at constant temperature) in, for example, a piston or gas syringe.

Example: Calculate the pressure when 100cm3 of gas at atmospheric pressure is compressed to 10cm3 at constant temperature.

Boyle's law states that PV is constant therefore the initial product of the pressure times the volume must equal the final product of the pressure times the volume, i.e.:

P1V1 = P2V2

P1 = 1.01 x 105 Pa, V1 = 0.1dm3, V2 = 0.01dm3, P2 = ?

P2 = (1.01 x 105 x 0.1)/0.01

P2 = 1.01 x 106 Pa
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