Dear student,

In calorimetry it is often desirable to know the heat capacity of the calorimeter itself rather than the heat capacity of the entire calorimeter system (calorimeter and water). The heat (q) released by a reaction or process is absorbed by the calorimeter and any substances in the calorimeter. If the only other substance in the calorimeter is water, the following energy balance exists:

q = q_cal + q_w

where q_cal is the heat flow for the calorimeter and q_w is the heat flow for the water.

Both of these individual heat flows can be related to the heat capacity and temperature change for the substance.

q_cal = C_cal ΔT

q_w = C_w ΔT

where C_cal is the heat capacity of the calorimeter and C_w is the heat capacity of the water. Because the water and calorimeter are in thermal equilibrium, they both have the same temperature and thus ΔT is the same for both. The consequence is that the heat capacity of the entire system (C) is the sum of the heat capacities for the individual components.

C = C_cal + C_w

The heat capacity is an extensive property; that is, the heat capacity depends upon the amount of substance present. The calorimeter exists as a fixed unit, thus its heat capacity is a fixed value. The amount of water in the calorimeter, however, can vary, and thus the heat capacity of the water can vary. When dealing with variable amounts of material, one often prefers to use an intensive measure of the heat capacity. One common intensive version of the heat capacity is the specific heat capacity (s), which is the heat capacity of one gram of a substance.

sw =

Cw mw

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All the best.

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Sagar Singh

B.Tech, IIT Delhi