Heat Capacities: Summary
Key points from this module:
- Heat capacities increase with temperature.
- For ideal gases, internal energy (U) and enthalpy (H) depend only on temperature, not pressure.
- For liquids and solids, U and H depend on temperature, but do not change significantly with pressure.
- Enthalpy changes with temperature for ideal gas mixtures can be calculated as the sum of ΔH values of the pure components.
- If heat of mixing is zero for a liquid mixture, enthalpy changes with temperature are the sum of ΔH values of the pure components.
- The NIST webbook (https://webbook.nist.gov/) is a good source for heat capacity data.
- This screencast demonstrates how to use the NIST WebBook to calculate enthalpy, and an example is shown in this spreadsheet.
From studying this module, you should now be able to:
- Calculate the final temperature when a given amount of heat is added to a gas, liquid, or solid.
- Calculate the amount of heat needed to raise a substance to a given temperature.
- Calculate enthalpy changes when more than one temperature-dependent heat capacity equation is required to cover the temperature range.
Prepared by John L. Falconer, Department of Chemical and Biological Engineering, University of Colorado Boulder