Solution Calorimetry PDF

# Solution Calorimetry Calorimetry is the experimental method of measuring the heat energy released or absorbed by a chemical reaction or physical process, such as by the combustion of a fuel. Energy changes that occur during chemical and physical changes are measured with a *device called a cal...

# Solution Calorimetry Calorimetry is the experimental method of measuring the heat energy released or absorbed by a chemical reaction or physical process, such as by the combustion of a fuel. Energy changes that occur during chemical and physical changes are measured with a *device called a calorimeter*. Calorimeters are constructed in such a way that the energy losses that occur in the simple experimental apparatus described earlier are minimised, enabling more accurate results. In a calorimeter, almost all of the heat energy released or absorbed is transferred directly to or from a measured volume of water. Two types of calorimeters are designed for measuring the energy changes in different types of reactions. - In solution calorimeters, the reaction takes place in a solution. - In bomb calorimeters, the reaction takes place in a sealed bomb vessel. This was described briefly in Section 3.3. ## Using a Solution Calorimeter Energy changes for reactions that occur in solution can be measured with a *solution calorimeter*. A solution calorimeter may be as simple as a polystyrene foam coffee cup with a lid, as shown in Figure 3.4.1. The insulation provided by the polystyrene foam prevents the transfer of heat to or from the surroundings of the calorimeter. The reaction is carried out in the calorimeter with an accurately known volume of water. The initial and final temperatures are measured and recorded, as are the amounts of reactants used. If the temperature of the water in the calorimeter increases, the reaction occurring in the calorimeter is an *exothermic reaction*. The reaction has released heat energy, the water in the calorimeter has absorbed that energy and the temperature of the water has increased. Similarly, if the temperature of the water in the calorimeter decreases, the reaction occurring in the calorimeter has absorbed energy from the water. In this case, the reaction is an *endothermic reaction*. A coffee cup solution calorimeter has some limitations. The polystyrene container absorbs some heat, so the temperature change is lower than it would otherwise be and the calculated value for the heat released or absorbed by the reaction is lower than it should be. A solution calorimeter cannot be used to measure the energy content of fuels or foods because the reaction in this case is a combustion reaction in which the fuel burns in oxygen. However, a solution calorimeter can be used to determine the energy change that occurs when a substance such as glucose dissolves in water. Solution calorimetry is used in the laboratory to determine the enthalpy changes that occur when acids react with bases, metals react with acids, and solids dissolve in water. The construction of a laboratory solution calorimeter is shown in Figure 3.4.2 on the following page. The stirrer is used to ensure the temperature of the water is uniform. If the temperature of the solution is not uniform, then the change in temperature measured as a result of the dissolution will not be accurate. The use of the electrical heater for calibrating the calorimeter is described in the next section.