Estimating heat capacity of solid compounds:\nWhich empirical rule is commonly used to approximate the molar heat capacity of a solid from its constituent atoms?

Introduction / Context:
Property estimation methods are vital when direct measurements are unavailable. For solids, one classical approach estimates the molar heat capacity from atomic contributions. Recognizing which rule applies helps in rapid preliminary calculations for materials and process design.

Given Data / Assumptions:

• We seek an empirical rule for solid heat capacity estimation.
• Idealized additive behavior by atoms in a crystal lattice is assumed.

Concept / Approach:
Kopp’s rule approximates the molar heat capacity (at constant pressure) of a solid compound as the sum of the atomic heat capacities of its constituent elements, each multiplied by their stoichiometric coefficients. It is particularly useful at moderate temperatures where quantum effects are modest.

Step-by-Step Solution:

Verification / Alternative check:
For salts like NaCl, summing Na and Cl atomic contributions via Kopp’s rule gives a reasonable first estimate compared with measured values, especially near room temperature.

Why Other Options Are Wrong:

• Clapeyron: phase equilibrium slope; not heat capacity estimation.
• Gibbs: general thermodynamic relations; not an estimation rule here.
• Trouton: approximate entropy of vaporization near boiling point.
• Raoult: solution vapor pressure, unrelated to solid heat capacity.

Common Pitfalls:
Overextending Kopp’s rule beyond its validity range or expecting high-precision predictions. Always validate against data when available.

Final Answer:
Kopp’s rule