Reaction-solution calorimetry

The principle of a solution calorimeter is simple. Aliquid reactant is contained in a Dewar, which is itself immersed in a thermostatic bath, usually kept at 298.15 K. Another reactant, either a liquid or a solid, is put in a small glass cell and immersed in the first liquid. Mixing is achieved mechanically. After the system comes to thermal equilibrium, the reaction is started by breaking the glass cell, to release the reactant inside the Dewar cell. The heat released or absorbed causes the temperature of the system to rise or drop, depending on the exo/endothermicity of the process. The reaction is allowed to go to completion and the temperature change is measured.

fig1

Figure 1. Dewar cell for anaerobic reaction-solution calorimetry.

 

The heat capacity of the solution calorimeter is calibrated by studying the reaction of a standard system. Commonly, the neutralization of TRIS (tris(hydroxymethyl)aminomethane) by HCl is used to standardize a solution calorimeter. Once the heat capacity of the calorimeter is known, any process in solution (reaction, mixing, precipitation, etc.) can be determined. The amount of heat absorbed by or removed from the solution can be calculated by the following equation.

q = c m ΔT (1)

where q represents the amount of heat transferred, c the specific heat of the solution, m the mass of the solution, and ΔT the temperature change associated with the process under study. A typical record for a exothermic process is shown below.