1. What Is Calorimetry?
Calorimetry is the method used to measure how much heat a substance gains or loses. Whenever two bodies at different temperatures come in contact, heat flows from the hotter one to the cooler one. Calorimetry helps calculate exactly how much heat has been transferred.
It is based on a simple idea: heat lost by the hotter substance equals heat gained by the cooler substance, provided no heat escapes to the surroundings.
2. Principle of Calorimetry
The principle of calorimetry states that when bodies exchange heat in an isolated system, the total heat lost equals the total heat gained. No heat is lost to the surroundings.
\( \, \text{Heat lost} = \text{Heat gained} \)
2.1. Reason Behind the Principle
Heat naturally flows from higher temperature to lower temperature until thermal equilibrium is reached. In a perfectly insulated setup, this exchange happens only between the bodies inside, so the total heat remains constant.
3. Heat Exchange Formula
The amount of heat gained or lost by a substance during temperature change is given by:
\( Q = mc\Delta T \)
Calorimetry uses this formula to find unknown quantities like final temperature, mass, or specific heat capacity.
3.1. What Each Symbol Means
- Q → Heat gained or lost (J)
- m → Mass of the substance (kg)
- c → Specific heat capacity
- ΔT → Change in temperature
4. Calorimeter
A calorimeter is a device designed to minimize heat loss so that accurate heat measurements can be made. It is usually made of materials that are poor conductors of heat and often includes an insulating jacket.
4.1. Parts of a Simple Calorimeter
- An insulated container (polishes or wooden jacket)
- A metal inner container (usually copper)
- A thermometer
- A stirrer to ensure uniform temperature
4.2. Why Insulation Is Important
Insulation ensures that heat does not escape to the surroundings. This keeps the system as close to ideal as possible so that the principle of calorimetry holds accurately.
5. Finding Final Temperature in Calorimetry
When a hot object is placed inside a cooler substance (like hot metal in water), both exchange heat until they reach the same final temperature. Using the heat exchange equation for both bodies allows calculating that final temperature.
5.1. General Equation
For two substances A (hot) and B (cool),
\( m_Ac_A(T_A - T_f) = m_Bc_B(T_f - T_B) \)
Here, \( T_f \) is the final equilibrium temperature.
6. Calorimetry and Change of State
Calorimetry can also measure heat involved in melting, freezing, boiling, or condensation. In these processes, temperature remains constant, but heat is absorbed or released.
6.1. Latent Heat Usage
During phase change, heat is given by:
\( Q = mL \)
where L is latent heat (fusion or vaporisation).
6.2. Example Situations
- Melting ice in warm water
- Condensing steam inside a calorimeter
Calorimetry helps measure the latent heat values in such cases.
7. Everyday Examples of Calorimetry
- Mixing hot and cold water and finding the final temperature.
- Cooling a hot metal object in a water bath.
- Finding how long food takes to cool down or warm up.
- Testing insulation quality of containers.