To determine the specific heat capacity of a given (i) solid and a (ii) liquid by the method of mixtures.
Heat is a form of energy that transfers from a body at higher temperature to a body at lower temperature when they are placed in contact. It is measured in calories.
The amount of heat required to raise the temperature of a substance by one degree (1 °C or 1 °K) is defined as the heat capacity
S= ∆Q/∆T
It is the amount of heat required to raise the temperature of unit mass of a substance through 1°C. Its S.I unit is J kg–1 K–1.
Specific heat, s = S / m
The branch of physics that deals with measurement of heat is called calorimetry.
According to the Principle of Calorimetry, if bodies of different temperatures (preferably a solid and a liquid) are brought in thermal contact, the amount of heat lost by the hot body is equal to the amount of heat gained by the cold body at thermal equilibrium, provided no heat is lost to the surrounding. The body at higher temperature releases the heat which is absorbed by the body at lower temperature. The heat transfer occurs until both the bodies attain the same temperature.
A device in which heat measurement can be made is called a calorimeter. It is designed to prevent or minimise the heat loss. Calorimeter consists of a metallic vessel and stirrer of the same material with high thermal conductance like copper or aluminium. The vessel is insulated from surrounding by keeping it inside a wooden jacket which contains heat insulating materials like glass wool etc. The outer jacket acts as a heat shield and reduces the heat loss from the inner vessel. The outer jacket has built in thermometer and stirrer. The stirrer is used to speed up reactions and heat transfer.
Calorimeter can be used to determine the heat capacity of a substance. When the sample say a solid is added to water or any liquid in the calorimeter, heat is exchanged between them as well as the calorimeter. Based on energy conservation, the heat lost by hot bodies will be equal to the heat gained by cold bodies. In this experiment,
Heat lost by the solid = heat gained by the liquid + heat gained by the calorimeter
The amount of heat lost/gained by the substance of mass m and specific heat s when its temperature rises or falls by ∆t is given by
∆Q = m s ∆t
Measurement of change in temperature of the water in calorimeter and knowledge of masses of substance involved helps in determining the heat gained or lost by each substance. This can be used to calculate the specific heat.
