What is a Calorimeter & How It Is Used In A Lab

If you’re looking to outfit your lab with a variety of analytical instruments, a calorimeter may be something you add to your list.  A calorimeter is a device used for calorimetry, or measuring heat capacity or the heat of physical changes or chemical reactions. In pharmaceuticals, they are used in drug design. In the chemical industry, they are used for quality control, and in biological studies, they are used for metabolic rate examination.

What Does A Calorimeter Do? 

A calorimeter measures the change in heat. Simple calorimeters are made with a metal container of water, positioned above a combustion chamber. A thermometer is used to measure the heat change in the amount of water. The simplest versions of the device can be made at home using two coffee cups or styrofoam cups, though it is not as accurate as lab equipment. There are, however, several other types that are much more complex.

The temperature of liquid changes when it loses or gains energy. The calorimeter measures the mass of the liquid along with the temperature change, to determine the amount of energy change.

It is different from a thermal analysis in that thermal analyzers measure properties of a material at various temperatures.

How A Calorimeter Works

Calorimeters are made with two vessels – an outer and an inner. The air between the two serves as a heat insulator, so there is little to no heat exchange between the contents of the inner vessel and the outside environment. Lab calorimeters use a fiber ring made with insulating material to keep the inner vessel in the center of the outer vessel. There is a thermometer to measure the temperature of the liquid in the inner container, and a stirrer to stir the liquid to distribute the heat throughout the container. 

If there is an exothermic reaction, one that releases thermal energy through heat or light, in the solution in the calorimeter, the temperature rises. If there is an endothermic reaction, one that absorbs thermal energy from the surroundings, heat is lost and the temperature decreases. If the two liquids do not transfer energy between them, the substances are in thermal equilibrium. The difference in temperature, along with the mass and specific heat of the solution, makes it possible to determine how much heat the reaction uses. 

The temperature change is used to calculate the enthalpy change per mole of substance A when substances A and B are reacted. The formula is:

q = Cv(Tf – Ti )

Q is the amount of heat in joules. 

Cv is the calorimeter’s heat capacity in joules per Kelvin (j/K)

Tf is the final temperature, and Ti is the initial temperature.

Types of Calorimeters 

  • Adiabatic: Adiabatic calorimeters are used to study runaway reactions. With this type, some heat is always lost. As a result, a correction factor is applied to compensate for that heat loss.
  • Reaction: With this type, chemical processes occur within a closed, insulated container. The heat flow vs. time is measured to determine the reaction heat. It’s used to find the maximum heat a reaction releases, or for reactions that need to run at a constant temperature.
    • Heat flow: With this type, a heating/cooling jacket controls the temperature of the physical process or the temperature of the jacket. The heat of the reaction is determined by measuring the temperature difference between the heat transfer fluid and the process fluid. It is necessary to know the fill volumes, specific heat, and heat transfer coefficient before a correct answer can be found.
    • Heat balance: With this type of calorimeter, the heating/cooling jacket controls the temperature of the process. Heat is measured by monitoring the heat that’s gained or lost by the transfer fluid.
    • Power compensation: This uses a heater added to the vessel so it maintains a constant temperature. The energy for the heater can be adjusted as the reaction requires. The calorimetry signal comes from electrical power.
    • Constant flux: This comes from heat balance calorimetry, but has a specialized control to maintain a constant flow of heat across the container wall.
  • Bomb Calorimeter: Also known as a constant-volume calorimeter, this is built to withstand the pressure that builds up as a result of a reaction as air heats in the reaction vessel. The change in water temperature is used to calculate the heat of combustion.
  • Calvet-type: This type uses a 3D fluxmeter sensor that’s made of a series of thermocouple rings. It is well-suited for larger sample size because it allows for a larger reaction container size, without affecting the measurement accuracy. 
  • Constant-pressure: The coffee cup calorimeter you can make at home is an example of a constant-pressure calorimeter. It measures the thermodynamic change in a solution, under constant pressure. 
  • Differential Scanning: With DSC, there are typically two pans, one sample pan, and one reference pan. The sample pan contains the sample while the reference pan remains empty. Each pan is heated separately at a specific rate, and this rate is maintained throughout the experiment. A computer system ensures that each pan heats up at the same rate, however, so that a measurement can be taken. The heater underneath the sample pan has to work harder than the empty reference pan, meaning it puts out more heat. The difference in the amount of heat put out is how a measurement is made.
  • Isothermal titration: In this type, the heat of reaction is used to follow a titration experiment. It’s possible to determine the midpoint of the reaction and its enthalpy and its binding affinity. It’s helpful in the pharmaceutical industry to classify potential drug candidates.

How Much do Calorimeters Cost? 

You can expect to spend anywhere from around $15,000 to $40,000 for a brand new calorimeter, depending on type and size. Used models can be found for as little as $9,000.

Leasing vs. Buying Calorimeter 

If your lab requires multiple calorimeters or other types of lab equipment such as TOC analyzers, elemental analyzers, or mass spectrometers, you’ll spend a significant amount of money upfront. To maximize your startup funds, consider leasing all the equipment you need. 

You’ll spend less at the start, and you’ll save over time because you don’t have to worry about the cost of maintenance and repair as it’s all included in your lease. Contact us today to learn more about how we can help.