Ideal Gas Equation (OCR A Level Physics)

• An ideal gas is a specific type of gas which:
  • Has molecules with negligible volume
  • Collisions which are elastic
  • Cannot be liquified
  • Has no interactions between the molecules (except during collisions)
  • Obeys the (ideal) gas laws (Boyles law, Charles’ law and Pressure law)

• All of these can occur at any temperature or pressure

• The ideal gas equation for number of moles can be expressed as:

• The ideal gas equation for number of molecules can also be written in the form:

• An ideal gas is therefore defined as:

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

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