Chapter 15.2, Problem 18SSC

Interpretation Introduction

Interpretation:

The use of a measured volume of water in a calorimeter is to be highlighted.

Concept introduction:

A calorimeter is a device used to measure the amount of heat released or absorbed in a process involving a chemical or physical change. In a calorimeter, a fixed amount of water is present. The system whose change in enthalpy has to be determined is kept inside the isolated system of calorimeter. If the system releases or absorbs heat from the isolated system of calorimeter, a change in temperature of the water is recorded by the thermometer.

Answer to Problem 18SSC

The exchange of heat between the system undergoing change, say A, and water of calorimeter is,

$\begin{array}{l}{Q}_A=-Q_{Water}\\ c_A\times m\times \Delta T_A=c_{Water}\times m\times \Delta T_{Water}\end{array}$

Since, the amount of water, specific heat capacity of water, and change in temperature of water are known, the unknowns of the system A can be determined.

Explanation of Solution

A calorimeter is as shown:

The calorimeter has a fixed quantity of water. A thermometer is dipped into the water. The calorimeter is airtight and behaves as an isolated system. When another changing system of mass, M is placed inside the calorimeter, the heat given off by it is absorbed by the water. As a result, the thermometer records an increase in the temperature of the water. This change in temperature along with the known parameters like the quantity of water can be used to determine the unknowns of the system of mass, M.

Conclusion

The measured volume of water inside a calorimeter is a fixed parameter. The only variable of the calorimeter is water temperature, which is used to determine the unknowns of the enclosed system.