Calorimetry

Calorimetry is the process of measuring the quantity of heat exchanged during chemical reactions, phase transitions (e.g., melting, boiling), or when materials are heated or cooled. The term originates from the Latin words “calor,” which means heat, and “metry,” meaning measurement.

1. Heat: It is a form of energy that flows between a system and its surroundings due to a temperature difference. Calorimetry focuses on quantifying this heat transfer.
2. Temperature vs. Heat: Temperature is a measure of the average kinetic energy of the particles in a substance. Heat is the total energy transferred between objects or systems due to a temperature difference.
3. Energy Conservation Principle: The principle of calorimetry is based on the First Law of Thermodynamics, which states that energy cannot be created or destroyed but can only transfer from one form to another. In a calorimetric process, the heat lost by one body is equal to the heat gained by another (in an isolated system).
4. Specific Heat Capacity: Specific heat capacity ($c$) is the amount of heat required to raise the temperature of 1 gram of a substance by 1°C (or 1 K). Calorimetry experiments often involve determining the specific heat of unknown substances.
5. Latent Heat: The energy required for a phase change (e.g., melting, boiling) without a change in temperature is known as latent heat. Calorimetry is used to measure the latent heat of fusion or vaporisation.

A calorimeter is a device used to measure the heat content of an object or the heat exchanged in a process (either produced or absorbed). It helps measure heat during physical changes (e.g., melting) or chemical reactions (e.g., combustion).

Calorimeter

Structure of a Calorimeter,

1. Double-walled Design: The calorimeter consists of two vessels: an inner vessel and an outer vessel. This setup is designed to prevent heat exchange between the inner contents and the external surroundings.

2. Materials: The inner vessel is made of copper because copper is a good conductor of heat and allows for precise heat transfer measurement. The outer vessel acts as an insulator, maintaining the inner vessel’s thermal isolation.

3. Additional Components

• Thermometer: Measures the temperature of the liquid or substance inside the calorimeter.
• Stirrer: Ensures uniform mixing so heat is evenly distributed within the liquid.

4. Thermal Isolation: Similar to a thermos flask, the design ensures no heat enters or leaves the calorimeter from or to the surroundings, maintaining accuracy.

• Water is added to the calorimeter, and its temperature is recorded using the thermometer. This temperature is the initial temperature (T_i​).
• The temperature of the water and the inner copper vessel becomes equal due to their contact.
• A hot object or a cold object is placed inside the water.
• Heat exchange occurs between the object, the water, and the calorimeter.
• Over time, all components (object, water, and calorimeter) reach a common final temperature (T_f​).
• The calorimeter’s isolation ensures no external interference with the heat exchange.

Heat Transfer:

1. Hot Object: If the object is hotter than the water, it loses heat. This heat is absorbed by the water and the calorimeter.
2. Cold Object: If the object is colder, it gains heat from the water and the calorimeter while they lose heat.

Principle of Conservation of Energy: The calorimeter is thermally isolated. Thus,

Heat lost by the object (Q_o​) = Heat gained by water (Q_w​) + Heat gained by calorimeter (Qc​).

Qo=Qw+Qc

​Heat Calculations:

1. Heat Formula: The heat Q gained or lost by a substance is calculated as: Q=m×c×ΔT

• m: Mass of the substance.
• c: Specific heat of the substance.
• ΔT: Change in temperature.

2. Substituting for Each Component:

• Object: Q_o=m_o×c_o×ΔT_o=m_o×c_o×(T_o−T_f)
• Water: Q_w=m_w×c_w×ΔT_w=m_w×c_w×(T_f−T_i)
• Calorimeter: Q_c=m_c×c_c×ΔT_c=m_c×c_c×(T_f−T_i)

3. Combined Equation:

• By substituting these into the energy balance equation: m_o×c_o×(T_o−T_f)=m_w×c_w×(T_f−T_i)+m_c×c_c×(T_f−T_i)

1. Measuring the specific heat capacity of unknown materials.
2. Determining the enthalpy of chemical reactions (e.g., combustion or neutralisation).
3. Analysing phase transitions like melting, boiling, or freezing.
4. Monitoring the heat released or absorbed in biological processes (e.g., metabolic studies).
5. Testing the energy content of fuels in industrial applications.
6. Assessing thermal properties of construction materials (e.g., insulation efficiency).
7. Studying heat transfer efficiency in engineering systems

A calorimeter is a cylindrical vessel which is used to measure the amount of heat gained (or lost) by a body when it is mixed with another body or substance.