Methods for estimating latent heat of vaporisation:\nWhich of the following is NOT typically used to compute latent heat?

Introduction / Context:
Latent heat of vaporisation is a key thermophysical property for distillation, evaporation, and energy balance calculations. Several correlations and thermodynamic relations allow its estimation when direct data is unavailable. Identifying which tools are appropriate speeds up preliminary design and troubleshooting.

Given Data / Assumptions:

• Equilibrium thermodynamics applies; vapor and liquid phases are at saturation conditions during phase change.
• Engineering correlations are accepted approximations.

Concept / Approach:
Common approaches include:
• Clausius–Clapeyron: Relates saturation pressure slope to latent heat; widely used for pure components at moderate ranges.
• Dühring and Othmer plots: Reference-substance methods correlating boiling points/enthalpies; useful when a similar well-characterized fluid exists.
• Kistyakowsky-type equations: Empirical correlations for enthalpy of vaporisation versus critical properties/temperature.
In contrast, Hess’s law pertains to the additivity of reaction enthalpies in chemical reactions, not phase-change latent heats of pure substances.

Step-by-Step Evaluation:

Verification / Alternative check:
Applying Clausius–Clapeyron: λ ≈ R T^2 (d ln Psat/dT) for a pure fluid; this directly ties λ to the vapor-pressure curve slope—standard in thermodynamics texts.

Why Other Options Are Wrong:

• (a), (b), (c) are established methods/correlations for latent heat; they are not incorrect choices.

Common Pitfalls:
Confusing chemical reaction enthalpy tools with phase-change properties; forgetting that latent heat refers to isothermal enthalpy change between phases at equilibrium.

Final Answer:
Hess’s law of constant heat summation