Ideal Gas Equation (OCR A Level Physics) : Revision Note

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.

Answer:

Step 1: State the known quantities

• Pressure, P = 4.5 × 10⁷ Pa 

• Volume, V = 8.3 × 10³ cm³ = 8.3 × 10³ × 10⁻⁶ = 8.3 × 10⁻³ m³

• Temperature, T = 15 °C = 15 + 273 = 288 K

Step 2: Write down the ideal gas equation

pV = nRT

Step 3: Rearrange for the number of moles n

Step 4: Substitute in values and calculate number of moles of gas

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