Chemistry · Thermodynamics · NEET
Calorimetry is the way we measure the heat change of a chemical or physical process. We do the process inside a vessel called a calorimeter. The calorimeter is placed in a known amount of liquid, usually water. When heat is released or absorbed, the temperature of the water changes. We measure that temperature change and calculate the heat. So calorimetry turns a temperature reading into a heat value.
The core formula is q = C x (delta T). Here q is the heat, C is the heat capacity of the water plus the calorimeter, and delta T is the temperature change (final minus initial). Heat capacity C tells you how much heat is needed to raise the temperature by 1 kelvin. If you know C and measure delta T, you get q directly. This is the single most important idea for NEET calorimetry questions.
The calorimeter vessel itself also soaks up some heat, not just the water. If you ignore it, your answer will be wrong. So you must know the heat capacity of the liquid AND the heat capacity of the calorimeter. NCERT says exactly this: 'Knowing the heat capacity of the liquid... and the heat capacity of calorimeter, it is possible to determine the heat evolved.' Add both when calculating q.
There are two ways to run a calorimetry experiment. At constant volume, you use a sealed bomb calorimeter, and the heat measured equals delta U (change in internal energy), because no work is done. At constant pressure (open to the air), the heat measured equals delta H (enthalpy change). NEET loves this link: q at constant V = delta U, and q at constant P = delta H.
The heat lost by the reaction equals the heat gained by the calorimeter, but with the opposite sign. NCERT states: 'heat lost by the system (reaction mixture) is equal to the heat gained by the calorimeter.' So if the water heats up, the reaction released heat, and q for the reaction is negative (exothermic). If the water cools down, the reaction absorbed heat, and q is positive (endothermic).
No. Calorimetry is the general technique of measuring heat. A bomb calorimeter is one specific device used for calorimetry at constant volume. There is also a constant-pressure (open) calorimeter. So bomb calorimeter is a type of calorimeter, not the whole subject. The next concept covers the bomb calorimeter in detail.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It measures the heat given out or taken in during a chemical reaction or a physical change, by tracking how the temperature of a known liquid changes.
Heat q is measured in joules (J) or kilojoules (kJ). Heat capacity C is in J/K, and temperature change delta T is in kelvin (K).
It gives delta U (change in internal energy), because at constant volume no pressure-volume work is done, so all the heat equals the internal energy change.
Usually water, because water has a well-known and high heat capacity, which makes temperature changes easy and reliable to measure.
It links a real measurement (temperature change) to thermodynamic quantities like delta U and delta H, which appear in Hess's law, enthalpy, and thermochemistry questions.
