Estimation rules – what does Kopp's rule calculate? Kopp's rule is a simple additive method used for estimating which thermophysical property of substances from atomic or group contributions?

Introduction / Context:
When experimental data are unavailable, engineers rely on estimation techniques. Kopp's rule is one of the classic group-additivity methods that provides first-cut estimates useful in material and energy balances and preliminary design.

Given Data / Assumptions:

• Applies primarily to molar heat capacities at constant pressure for solids (and sometimes liquids) at moderate temperatures.
• Property contributions are additive over atoms or structural groups.

Concept / Approach:
Kopp's rule states that the molar heat capacity of a compound is approximately the sum of the atomic heat capacities of its constituent elements (or group contributions). While rough, it often yields acceptable estimates near room temperature. It is not designed for conductivity, viscosity, or surface tension, which require different correlations and are more sensitive to structure and state.

Step-by-Step Solution:

Verification / Alternative check:
Comparison with tabulated Cp values shows Kopp's rule typically within reasonable error for many inorganic solids at ambient conditions.

Why Other Options Are Wrong:

• Thermal conductivity, viscosity, surface tension: Not additive in the same simple way; these depend strongly on microstructure and temperature with no universally valid Kopp-style rule.

Common Pitfalls:
Applying Kopp's rule at high temperatures or to substances with strong anharmonic effects; neglecting phase changes where Cp varies markedly.

Final Answer:
heat capacity.