How Calorimetry Works & How Leasing Benefits Your Lab

This thermal analysis technique is used to look at heat exchange inside a system without having any heat transfer to its surroundings. This type of process is referred to as adiabatic. Ideally, when heat is generated in this type of setup, 100% of that heat will go toward increasing the system’s temperature, feeding the reaction.

The reaction will then generate more heat, accelerating the increase in temperature, and thus, the reaction. These devices are used to study so-called “runaway reactions” for this reason. It is important to note that no adiabatic calorimeter is completely adiabatic.

When looking at exothermic or endothermic properties of a chemical reaction, a reaction calorimeter is used. These devices are composed of an insulated jacket surrounding a reaction container.

The temperature measurement device should be submerged within the container. There are four main subcategories for reaction calorimeters:

• Heat Flow: This method focuses on the heat flow as it passes across the reactor’s wall. This means that the heat input or output is transferred from the insulating jacket to the samples. This then can be used to determine the amount of heat per unit of area per unit of time that is transferred. This is referred to as the heat flux.
• Heat Balance: The heat loss or gain of the process is controlled by the heating or cooling of the insulating jacket in this type. The heat transfer fluid is observed to determine any change in heat of the system.
• Power Compensation (PCC): A cooling jacket working at a constant temperature and a constant flow rate is used and the process temperature is controlled by adjusting the power being fed to an electrical heater. The power of the electrical heater is varied to maintain the desired temperature throughout the process.
• Constant Flux: Maintaining a constant temperature of the insulated jacket, constant flux calorimetry instead varies the area that the heat transfer occurs over by varying the geometry of the jacket.

Constant volume calorimeters, also known as bomb calorimeters, measure the heat energy of a reaction in an environment with a constant volume. Bomb calorimetry is used to look at temperature change within a combustion reaction.

Since the volume must remain the same, bomb calorimeters are built to withstand immense pressure that increases while the reactions occur within them. The basic components that make up this device include:

• The sample.
• Reactants like ignition wires that cause a reaction.
• A steel bomb, or stainless steel container, which acts as the reaction vessel. It is often submerged in the surrounding water and held inside an insulated container.

Additionally, there is a thermometer and a stirrer that monitor and move the water in the container.

As the name indicates, constant pressure calorimeters provide a constant pressure environment to measure the enthalpy change of a reaction, a material’s aversion to change. A simple example would be what is known as a coffee-cup calorimeter.

These calorimeters consist of two Styrofoam coffee cups nested in one another with a lid on top that has a hole for the thermometer and a stirring rod. A known solvent (such as water) is stored inside the innermost cup. With the outer cup acting as an insulator, the heat of combustion from the reaction is absorbed into the solvent and measured with the thermometer.

Constant pressure calorimeters are also called isobaric calorimeters.

These devices observe how changes in a material’s temperature alter its heat capacity. While using a known material and monitoring the change in heat capacity, phase and physical changes can be detected with accuracy.

The speed and ease with which this thermal analysis technique can cause materials to hit these transition points are the reason why it is such a commonly used method.

There are two approaches to DSC, heat flux DSC and heat flow DSC.

• Heat Flow: This device measures the flow of thermal energy into a sample in one container by comparing it to the flow of thermal thermal energy into a separate reference container. In both cases, the containers are kept at a constant temperature through the entire reaction.
• Heat Flux: Similar to heat flow DSC, heat flux DSC compares the temperature difference between the sample and reference container as the temperature rise or fall occurs at a constant rate.

ITC is a technique used for quantitative studies of a wide variety of biomolecular reactions. It works by directly measuring the amount of heat that is either released or absorbed during a biomolecular binding event. Furthermore, ITC is the only technique capable of simultaneously measuring all binding parameters within a single experiment.

Being able to measure the heat transfer during binding enables accurate determination of binding constants (KD), reaction stoichiometry (n), enthalpy (∆H) and entropy (ΔS). This holistic view provides a complete thermodynamic profile of the molecular interaction. Isothermal titration calorimetry can also shed light on the mechanisms that underlie molecular interactions.

This deeper understanding of structure-function relationships offers scientists and researchers the confidence to make decisions in both hit selection and lead optimization.

At its heart, calorimeters and calorimetry use known physical or environmental properties to find unknown thermal properties of materials. Each method of calorimeter changes a different known variable and observes how that changes the sample’s amount of energy.

The many different types of methods, calibrations, and classifications of these types of equipment go to show how complex and specific thermal analysis can be.

Calorimetry can even be found in particle physics in the form of hadron and electromagnetic calorimeters. Both are used to better understand the smallest known units of matter in our universe by studying the heat energy of particles.

A hadronic calorimeter is currently being used at the European Organization for Nuclear Research (CERN) in the study of the Higgs-Boson particle, however, not every application is so complex. The labels of any drink or food product that show how many calories are in food are derived using calorimetry.