D17.3 Heat Capacity and Calorimetry

Heat Capacity

The specific heat capacity (c) of a substance is the heating required to raise the temperature of 1 g of a substance by 1 °C. (Because 1 K is the same size as 1 °C, ΔT has the same numeric value whether expressed in K or °C.)

If we know the mass, m, of a sample and its specific heat capacity, c, we can calculate the heat transfer of energy to or from the sample by measuring the temperature change during heating or cooling:

q = m·c·ΔT = m·c·(Tfinal – Tinitial)

The sign of ΔT tells us whether the substance is being heated (positive value for q) or cooled (negative q ).

Exercise: Heat Transfer of Energy

Exercise: Heating a Hot Tub

Calorimetry

Calorimetry is an experimental technique used to quantitatively measure heat transfer of energy. In calorimetry it is useful to define a system, the substance(s) undergoing the chemical or physical change, and the surroundings, everything else that can exchange energy with the system.

When we apply calorimetry to determine the heat transfer of energy involved in chemical reactions,

qreaction = –qsurroundings

Here, qreaction is defined as the change in energy of all atoms present in reactants and products.

A reaction in which there is heat transfer from the reacting substances to their surroundings (a reaction that heats the surroundings) is an exothermic reaction. For example, the combustion reaction that occurs in the flame of a lit match is exothermic. A reaction in which there is heat transfer from the surroundings to the reacting substances (a reaction that cools the surroundings) is an endothermic reaction. For example, when the substances in a cold pack (water and a salt such as ammonium nitrate) are mixed, the resulting process transfers energy from the surroundings, making the surroundings colder.

Activity: Energy Transfer to a Cold Pack

For additional review materials pertaining to heat capacity, calorimetry and heat measurements, see here.

Comments
Please use this form to report any inconsistencies, errors, or other things you would like to change about this page. We appreciate your comments. 🙂

License

Icon for the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License

Chemistry 109 Fall 2021 by John Moore, Jia Zhou, and Etienne Garand is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.