Thermal equation of state and critical point

Principle

A substance which is gaseous under normal conditions is enclosed in a variable volume and the variation of pressure with the volume is recorded at different temperatures. The critical point is determined graphically from a plot of the isotherms.

Benefits

• Visualization of the critical point

Tasks

1. Measure a number of p-V isotherms of ethane.
2. Determine the critical point and the critical quantities of ethane.
3. Calculate the constants of the Van der Waals equation, the Boyle temperature, the radius of the molecules and the parameters of the interaction potential.

Learning objectives

• Ideal gases
• Real gases
• Equations of state
• Van der Waals equation
• Boyle temperature
• Critical point
• Interaction potential
• Molecule radius