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EEJ MAIN Chemistry QUESTION #7179
Question 1
What is the correct SI unit for the van der Waals parameter '$a$' as used in the equation $(P + \frac{an^{2}}{V^{2}})(V - nb) = nRT$?
  • $atm \text{ dm}^{6} \text{ mol}^{-2}$✔️
  • $kg \text{ m s}^{-1}$
  • $kg \text{ m s}^{-2}$
  • $dm^{3} \text{ mol}^{-1}$
Correct Answer Explanation
The term $\frac{an^{2}}{V^{2}}$ must have the same units as pressure ($P$).
  • $[a] = \frac{P \times V^{2}}{n^{2}}$
  • In common units, this translates to $\text{atm} \times (\text{dm}^{3})^{2} / \text{mol}^{2}$
  • Result: $atm \text{ dm}^{6} \text{ mol}^{-2}$