Additivity of atomic heat (Kopp’s rule): Kopp’s rule is most useful for estimating which of the following?

Introduction / Context:
Kopp’s rule provides a simple, empirical way to estimate the heat capacity of crystalline solids from their constituent elements. It relies on the approximate additivity of atomic heat capacities, and while not exact, it offers useful first estimates in materials and process calculations where precise data are unavailable.

Given Data / Assumptions:

• Kopp’s rule applies primarily to solid inorganic compounds.
• Each element contributes an approximately constant atomic heat to the molar heat capacity of the solid compound.
• Temperature effects and structural peculiarities can cause deviations.

Concept / Approach:
For a solid compound A_xB_y…, the molar heat capacity at constant pressure, Cp,m, is approximated as the sum of the atomic heat capacities of the elements multiplied by their stoichiometric coefficients. This contrasts with gas-phase correlations that depend strongly on temperature and molecular degrees of freedom (translation, rotation, vibration), for which Kopp’s rule is not used.

Step-by-Step Solution:

Verification / Alternative check:
Handbooks show Kopp’s estimates often within acceptable engineering tolerance for many salts and oxides, especially at moderate temperatures, though modern data are preferred when available.

Why Other Options Are Wrong:

• Gas heat capacities (molal or otherwise): depend on molecular degrees of freedom; Kopp’s rule is not applied.
• Activation energy and latent heats: unrelated physical quantities.

Common Pitfalls:
Using Kopp’s rule for molecular gases or polymers where it is not valid; ignoring temperature dependence.

Final Answer:
Heat capacities of solids