Calorimetry – Class 11 | Chapter – 11 | Physics Short Notes Series PDF for NEET & JEE
Calorimetry: A calorimeter is a device used to measure the amount of heat transferred in a physical or chemical process. It works by measuring changes in temperature resulting from the transfer of heat between the system being studied and a surrounding environment.
There are two main types of calorimeters: bomb calorimeters and solution calorimeters.
Bomb calorimeters are used to measure the heat of combustion of a substance. They typically consist of a small metal chamber called a bomb that is filled with a known mass of the substance and placed in a surrounding container filled with oxygen. The bomb is then ignited, causing the substance to burn and release heat. The heat is transferred to the surrounding water, and the resulting temperature change is measured. By knowing the mass of the substance burned, the heat capacity of the calorimeter, and the temperature change, the heat of combustion of the substance can be calculated.
Solution calorimeters, on the other hand, are used to measure the heat of reaction of a solution. They typically consist of a small insulated container filled with a known amount of solution and surrounded by a surrounding environment. The container is stirred to ensure uniform mixing, and the temperature change resulting from the reaction is measured. By knowing the heat capacity of the calorimeter and the temperature change, the heat of reaction can be calculated.
Calorimeters are used in many fields, including chemistry, physics, and engineering, to measure the heat released or absorbed during chemical reactions, phase transitions, and other processes. They are important tools for understanding and controlling the transfer of heat in many different applications.
Principle of Calorimetry
The principle of calorimetry is based on the concept of heat transfer. Calorimetry is the science of measuring the amount of heat exchanged between a system and its surroundings. The principle of calorimetry is based on the first law of thermodynamics, which states that energy cannot be created or destroyed, only converted from one form to another. Therefore, the heat lost by one object or system is equal to the heat gained by the other object or system.
In calorimetry, a system is placed in a calorimeter, which is a device used to measure heat exchange. The calorimeter is designed to minimize heat exchange between the system and its surroundings, except for the heat exchange being studied. For example, if the system being studied is a chemical reaction, the calorimeter is designed to minimize heat exchange with the environment, except for the heat generated or absorbed by the chemical reaction.
The heat exchange between the system and its surroundings is measured by monitoring the temperature change of the system and its surroundings. The temperature change is related to the heat exchanged by the following equation:
Q = mcΔT
where:
- Q is the amount of heat exchanged
- m is the mass of the system or surroundings
- c is the specific heat capacity of the system or surroundings
- ΔT is the change in temperature of the system or surroundings
By measuring the temperature change of the system and surroundings, and knowing their masses and specific heat capacities, the amount of heat exchanged can be calculated. This allows for the determination of various thermodynamic properties, such as the heat of reaction, enthalpy, and entropy.
Overall, the principle of calorimetry is to measure the amount of heat exchanged between a system and its surroundings, and to relate this heat exchange to various thermodynamic properties of the system. This principle has numerous applications in chemistry, physics, and engineering, and is an essential tool for understanding and controlling the transfer of heat in many different systems.
Structure of Calorimeter
The structure of a calorimeter depends on its type and intended application. There are different types of calorimeters used for different purposes, but they all share a common goal of measuring heat exchange.
The most common types of calorimeters are solution calorimeters and bomb calorimeters.
Solution calorimeters are used to measure the heat exchange between a solution and its surroundings. They typically consist of an insulated container that holds the solution, a temperature probe to measure the temperature change, and a stirrer to ensure uniform mixing of the solution. The container is surrounded by a water bath or air jacket to minimize heat exchange with the environment. The calorimeter is designed to be well-insulated to minimize heat transfer between the solution and the environment, except for the heat being studied.
Bomb calorimeters are used to measure the heat of combustion of a substance. They consist of a small metal chamber (the bomb) that holds the substance being burned, surrounded by a water bath. The bomb is filled with oxygen and ignited, causing the substance to burn and release heat. The heat is transferred to the surrounding water, and the resulting temperature change is measured.
In both types of calorimeters, the temperature change is monitored using a thermometer or temperature probe. The mass of the sample and other relevant parameters such as the heat capacity of the calorimeter, and the specific heat of the sample and surrounding materials are also measured or known. From these measurements, the heat exchange can be calculated using the principle of calorimetry.
Overall, the structure of a calorimeter depends on its intended application, but it generally consists of an insulated container, a temperature probe or thermometer, and a way to minimize heat exchange with the environment. The structure of a calorimeter is designed to ensure accurate measurement of the heat exchange between a system and its surroundings, allowing for the determination of various thermodynamic properties.
Formula of Calorimeter
The formula used in calorimetry is based on the principle of conservation of energy, which states that the energy in a closed system is constant. The formula relates the amount of heat exchanged to the mass, specific heat capacity, and temperature change of the system and its surroundings.
The formula used in calorimetry is:
Q = m * c * ΔT
where:
- Q is the amount of heat exchanged (in Joules, J)
- m is the mass of the system or surroundings (in grams, g)
- c is the specific heat capacity of the system or surroundings (in J/g°C)
- ΔT is the change in temperature of the system or surroundings (in °C)
If the system is undergoing a chemical reaction, the heat of reaction (ΔH) can be calculated using the following formula:
ΔH = -Q / n
where:
- ΔH is the heat of reaction (in J/mol)
- Q is the amount of heat exchanged (in J)
- n is the number of moles of the limiting reactant
Overall, the formula used in calorimetry allows for the determination of the amount of heat exchanged between a system and its surroundings, and the calculation of various thermodynamic properties, such as the heat of reaction, enthalpy, and entropy.
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