5.2 Calorimetry

calorimeter.

A calorimeter is a device used to measure the amount of heat involved in a chemical or physical process. For example, when an exothermic reaction occurs in solution in a calorimeter, the heat produced by the reaction is absorbed by the solution, which increases its temperature. For example, when an exothermic reaction occurs in solution in a calorimeter, the heat produced by the reaction is absorbed by the solution, which increases its temperature

nutritional calorie (Calorie)

A nutritional calorie (Calorie) is the energy unit used to quantify the amount of energy derived from the metabolism of foods; one Calorie is equal to 1000 calories (1 kcal), the amount of energy needed to heat 1 kg of water by 1 °C.

calorimetry

One technique we can use to measure the amount of heat involved in a chemical or physical process is known as calorimetry. Calorimetry is used to measure amounts of heat transferred to or from a substance. To do so, the heat is exchanged with a calibrated object (calorimeter)

How do we measure this heat?

The measurement of heat transfer using this approach requires the definition of a system and its surroundings

When an endothermic reaction occurs, the heat required is

When an endothermic reaction occurs, the heat required is absorbed from the thermal energy of the solution, which decreases its temperature. The temperature change, along with the specific heat and mass of the solution, can then be used to calculate the amount of heat involved in either case.

surroundings

all other matter, including components of the measurement apparatus, that serve to either provide heat to the system or absorb heat from the system

bomb calorimeter

bomb calorimeter, is used to measure the energy produced by reactions that yield large amounts of heat and gaseous products, such as combustion reactions. (The term "bomb" comes from the observation that these reactions can be vigorous enough to resemble explosions that would damage other calorimeters.)

This relationship can be rearranged to show that the heat gained by substance M is equal to the heat lost by substance W:

q substance M = −q substance W

Because energy is neither created nor destroyed during a chemical reaction, the heat produced or consumed in the reaction (the "system"), qreaction, plus the heat absorbed or lost by the solution (the "surroundings"), qsolution, must add up to zero:

qreaction + qsolution = 0

This means that the amount of heat produced or consumed in the reaction equals the amount of heat absorbed or lost by the solution:

qreaction = −qsolution

If this occurs in a calorimeter, ideally all of this heat transfer occurs between the two substances, with no heat gained or lost by either its external environment. Under these ideal circumstances, the net heat change is zero:

qsubstance M + qsubstance W = 0

calorimeter

the heat is exchanged with a calibrated object. The temperature change measured by the calorimeter is used to derive the amount of heat transferred by the process under study.

system

the substance or substances undergoing the chemical or physical change

If the amount of heat absorbed by a calorimeter is too large to neglect or if we require more accurate results, then

we must take into account the heat absorbed both by the solution and by the calorimeter.