CALORIMETRY: WHAT IT STUDIES AND APPLICATIONS - CHEMISTRY - 2025

The calorimetry is a technique that determines the changes of the caloric content of a system associated with a chemical or physical process. It is based on the measurement of temperature changes when a system absorbs or emits heat. The calorimeter is the equipment used in reactions in which a heat exchange is involved.

What is known as a "coffee cup" is the simplest form of this type of appliance. By using it, the amount of heat involved in reactions carried out at constant pressure in an aqueous solution is measured. A coffee cup calorimeter consists of a polystyrene container, which is placed in a beaker.

The water is placed in the polystyrene container, equipped with a lid made of the same material that gives it a certain degree of thermal insulation. In addition, the container has a thermometer and a mechanical stirrer.

This calorimeter measures the amount of heat that is absorbed or emitted, depending on whether the reaction is endothermic or exothermic, when a reaction takes place in an aqueous solution. The system to be studied is made up of the reactants and the products.

What does calorimetry study?

Calorimetry studies the relationship between the heat energy associated with a chemical reaction, and how it is used to determine its variables. Their applications in research fields justify the scope of these methods.

Caloric capacity of a calorimeter

This capacity is calculated by dividing the amount of heat absorbed by the calorimeter by the change in temperature. This variation is the product of the heat that is emitted in an exothermic reaction, which is equal to:

Amount of heat absorbed by the calorimeter + amount of heat absorbed by the solution

The variation can be determined by adding a known amount of heat by measuring the change in temperature. For this determination of heat capacity, benzoic acid is usually used, since its heat of combustion (3,227 kJ / mol) is known.

Caloric capacity can also be determined by adding heat using an electric current.

Example

A 95 g bar of a metal is heated to 400 ºC, immediately taking it to a calorimeter with 500 g of water, initially at 20 ºC. The final temperature of the system is 24 ºC. Calculate the specific heat of the metal.

Δq = mx ce x Δt

In this expression:

Δq = load variation.

m = mass.

ce = specific heat.

Δt = temperature variation.

The heat gained by the water is equal to the heat given off from the metal bar.

This value is similar to the one that appears in a table of the specific heat for silver (234 J / kg ºC).

So one of the applications of calorimetry is cooperation for the identification of materials.

Calorimetric pump

It consists of a steel container, known as the pump, resistant to the high pressures that can arise during the reactions that occur in this container; This container is connected to an ignition circuit to start the reactions.

The pump is immersed in a large container with water, whose function is to absorb the heat that is generated in the pump during the reactions, making the temperature variation small. The water container is equipped with a thermometer and a mechanical stirrer.

Energy changes are measured at virtually constant volume and temperature, so no work is done on the reactions that occur in the pump.

ΔE = q

ΔE is the variation of the internal energy in the reaction and q the heat generated in it.

Types of calorimeter

Isothermal Titration Calorimeter (CTI)

The calorimeter has two cells: in one the sample is placed and in the other, the reference, water is generally placed.

The temperature difference that is generated between the cells - due to the reaction that occurs in the sample cell - is canceled out by a feedback system that injects heat to equalize the temperatures of the cells.

This type of calorimeter allows to follow the interaction between macromolecules and their ligands.

Differential Scanning Calorimeter

This calorimeter has two cells, like the CTI, but it has a device that allows the temperature and heat fluxes associated with changes in a material to be determined as a function of time.

This technique gives information about the folding of proteins and nucleic acids, as well as their stabilization.

Applications

-The calorimetry allows to determine the heat exchange that occurs in a chemical reaction, thus allowing a clearer understanding of its mechanism.

-By determining the specific heat of a material, calorimetry provides data that helps to identify it.

-As there is a direct proportionality between the heat change of a reaction and the concentration of the reactants, coupled with the fact that calorimetry does not require clear samples, this technique can be used to determine the concentration of substances present in complex matrices.

-In the field of chemical engineering, calorimetry is used in the safety process, as well as in different fields of the optimization process, chemical reaction and in the operating unit.

Uses of isothermal titration calorimetry

-Collaborates in the establishment of the enzyme action mechanism, as well as in its kinetics. This technique can measure reactions between molecules, determining binding affinity, stoichiometry, enthalpy, and entropy in solution without the need for markers.

-Assesses the interaction of nanoparticles with proteins and, in conjunction with other analytical methods, is an important tool to record the conformational changes of proteins.

-It has application in the preservation of food and crops.

-As for the preservation of food, you can determine its deterioration and shelf life (microbiological activity). You can compare the efficiency of different food preservation methods, and you are able to determine the optimal dose of preservatives, as well as the degradation in the packaging control.

-As for vegetable crops, you can study the germination of the seed. Being in water and in the presence of oxygen, they release heat that can be measured with an isothermal calorimeter. Examine the age and improper storage of the seeds and study their growth rate under variations in temperature, pH or different chemicals.

-Finally, it can measure the biological activity of soils. In addition, it can detect diseases.

Uses of Differential Scanning Calorimetry

-Together with isothermal calorimetry, it has made it possible to study the interaction of proteins with their ligands, the allosteric interaction, the folding of proteins and the mechanism of their stabilization.

-You can directly measure the heat that is released or absorbed during a molecular bonding event.

-Differential scanning calorimetry is a thermodynamic tool for the direct establishment of the uptake of heat energy that occurs in a sample. This makes it possible to analyze the factors involved in the stability of the protein molecule.

-It also studies the thermodynamics of the nucleic acid folding transition. The technique allows the determination of the oxidative stability of linoleic acid isolated and coupled to other lipids.

-The technique is applied in the quantification of nanosolids for pharmaceutical use and in the thermal characterization of nanostructured lipid transporters.

References

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7. Community College Consortium for Bioscience Credentials. (July 7, 2014). Coffee cup calorimeter.. Retrieved on June 7, 2018, from: commons.wikimedia.org