Ideal Gas Equation
- 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 equation of state for an ideal gas (or the ideal gas equation) can be expressed as:
- The ideal gas equation 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
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
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
Examiner Tip
Don’t worry about remembering the values of R and k, they will both be given in the equation sheet in your exam.
