Principles of Calorimetry
Calorimetry is a scientific experimental measurement of the change of heat of a substance. A calorimeter is usually the container in which the heat change experiment is conducted. Calorimetry means “measuring heat”. When two bodies (one being solid and other being liquid or both being liquid) at different temperatures are mixed, heat will be transferred from the body at higher temperature to the body at lower temperature till both acquire same temperature. The body at higher temperature releases heat while the body at lower temperature absorbs it, so that Heat lost = Heat gained.
I.e. Principle of Calorimetry represents the law of conservation of heat energy. Temperature of mixture (θmax) is always ≥ lower temperature (θL) and ≤ higher temperature (θH), i.e., θL ≤ θmax ≤ θH.
It means that the temperature of mixture can never be lesser than lower temperature (as a body can’t be cooled below the temperature of cooling body) and greater than higher temperature (as a body can’t be heated above the temperature of heating body). Furthermore, usually rise in temperature of the other body. Though, heat gained by one body is equal to the heat lost by the other.
Mixing of Two Substance when Temperature changes only: It means that there is no phase change. Supposes that two substances having masses m₁ and m₂ gram specific heats C₁ and C₂, temperatures θ₁ and θ₂ (θ₁ > θ₂) are mixed together such that temperature of mixture at equilibrium is θmax.
Hence, Heat lost = Heat gained.
m₁C₁ (θ₁ – θmax) = m₂C₂ (θmax – θ₂).
∴ \(\theta =\frac{{{m}_{1}}{{C}_{1}}{{\theta }_{1}}+{{m}_{2}}{{C}_{2}}{{\theta }_{2}}}{{{m}_{1}}{{C}_{1}}+{{m}_{2}}{{C}_{2}}}\).