Real Gases and van der Waals Equation
Real gases deviate from ideality because molecules occupy volume and attract one another, corrections captured by the van der Waals equation.
What is Real Gases and van der Waals Equation?
Real gases deviate from ideality because molecules occupy volume and attract one another, corrections captured by the van der Waals equation.
Key formula / rule: Z = PV/nRT equals one for an ideal gas.
Key points
- Analyse deviations from ideal behaviour using the compressibility factor.
- Compare the ideal and van der Waals equations term by term.
Common exam trap
Assuming all deviations push Z in the same direction.
Definitions
- Term
Real Gases and van der Waals Equation
- Meaning
Real gases deviate from ideality because molecules occupy volume and attract one another, corrections captured by the van der Waals equation.
- Term
Real Gases and van der Waals Equation — explanation
- Meaning
The compressibility factor Z measures deviation, dropping below one where attractions dominate and rising above one where finite molecular volume dominates. Deviations are largest at high pressure and low temperature.
Learning objectives
Analyse deviations from ideal behaviour using the compressibility factor.
Compare the ideal and van der Waals equations term by term.
Formulae
- Key point
Z = PV/nRT equals one for an ideal gas.
- Key point
The constant a corrects for attraction and b for molecular volume.
- Key point
Deviations are greatest near the critical point.
Prerequisites
CHE-U1-TH-T1-S1-C1
Common mistakes
Assuming all deviations push Z in the same direction.
Treating a and b as universal constants rather than gas-specific.
Keywords
Real
Gases
Waals
Equation
Practice preview
The two main corrections introduced in the ideal gas equation to derive the van der Waals equation for real gases account for:…
easy
In the van der Waals equation, the constant 'a' is a measure of:…
easy
For a gas with a very high value of van der Waals constant 'a' and a very low value of constant 'b', which of the following statements is most likely true?…
medium