AQA A Level Physics

Revision Notes

6.5.3 Ideal Gas Equation

Ideal Gas Equation

  • The equation of state for an ideal gas (or the ideal gas equation) can be expressed as:

Ideal gas equation

  • The ideal gas equation can also be written in the form:

Ideal gas equation 2

  • An ideal gas is therefore defined as:

A gas which obeys the equation of state pV = nRT at all pressures, volumes and temperatures

Worked Example

A storage cylinder of an ideal gas has a volume of 8.3 × 103 cm3.

The gas is at a temperature of 15 °C and a pressure of 4.5 × 107 Pa.

Calculate the amount of gas in the cylinder, in moles.

Step 1: Write down the ideal gas equation

Since the number of moles (n) is required, use the equation:

pV = nRT

Step 2: Rearrange for the number of moles n

Ideal Gas Equation equation 1

Step 3: Substitute in values

V = 8.3 × 103 cm3 = 8.3 × 103 × 10-6 = 8.3 × 10-3 m3

T = 15 °C + 273.15 = 288.15 K

Ideal Gas Equation equation 2

Exam Tip

Don’t worry about remembering the values of R and k, they will both be given in the equation sheet in your exam.

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