Properties of an ideal Raoultian solution:\nFor a solution that strictly obeys Raoult’s law, what are ΔH_mix and ΔV_mix on mixing?

Difficulty: Easy

Correct Answer: both ΔH_mix = 0 and ΔV_mix = 0

Explanation:


Introduction / Context:
When liquid mixtures behave ideally, design calculations simplify dramatically because activities equal mole fractions. Recognizing the thermodynamic hallmarks of ideality helps in VLE modeling and quick feasibility studies.


Given Data / Assumptions:

  • Ideal solution behavior (Raoult’s law holds over full composition range).
  • Mixing occurs at constant temperature and pressure.


Concept / Approach:
Ideality implies no enthalpy or volume effects on mixing. Hence, ΔH_mix = 0 (no heat released/absorbed) and ΔV_mix = 0 (no contraction/expansion). This reflects indistinguishable unlike/like interactions and activity coefficients near unity (γ_i ≈ 1).


Step-by-Step Solution:
State the ideal-solution criteria.Map them to thermodynamic statements: ΔH_mix = 0 and ΔV_mix = 0.Choose the option containing both equalities.


Verification / Alternative check:
Empirical data for near-ideal pairs (like benzene–toluene) show negligible heat and volume changes upon mixing, validating these criteria.


Why Other Options Are Wrong:
Options with nonzero ΔH or ΔV describe nonideal mixtures exhibiting positive/negative deviations from Raoult’s law.


Common Pitfalls:
Believing only one of the two (ΔH or ΔV) must be zero; both are required for strict ideality.


Final Answer:
both ΔH_mix = 0 and ΔV_mix = 0

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