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The unit of the van der Waals gas equation parameter 'a' in (P + a n²/V²)(V - nb) = nRT is:

1. kg m s⁻²
2. dm³ mol⁻¹
3. kg m s⁻¹
4. atm dm⁶ mol⁻²

Correct answer: atm dm⁶ mol⁻²

Solution

The parameter 'a' in the van der Waals equation accounts for the attractive forces between gas molecules, and its units must reflect pressure multiplied by volume squared per mole squared. Therefore, the correct unit is atm dm⁶ mol⁻², which aligns with the dimensional analysis of the equation.

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