# Thermal Properties of Matter

## 8. Calorimetery

• Calorimetery means measurement of Heat.
• Calorimeter is the device used to measure heat and it is cylinderical vessel made of copper and provided by a stirrer and a lid.
• This vessel is kept in a wooden block to isolate it thermally from suroundings.A theromometer is used to measure the temperature of the content in the calorimeter.
• When bodies at diffrent temperature are mixed in a calorimeter,they exchange heat with each other.
• Bodies at higher temperature loose heat while bodies at low temperature gain heat.Contents of the calorimeter is continously stirred to keep temperature of contents uniform
• Thus principle of calorimetery states that the total heat given by hot objects is equal to the total heat received by cold objects.

## 9.Change of phases:

• There are three phases of matter i.e, Solid, Liquid and Gas.
• Substance for example, H2O exists in solid phase as Ice,in liquid phase as Water and in gas state as Steam.
• Transtion from one phase to another phase are accompained by absorption or liberation of heat and usually by change in volume even at constant T.
• Change of phase from solid to liquid is called melting , from liquid to solid is called fusion and from liquid to gas is called vaporisation
• Once the temperature for phase change is reached( e,g melting or boiling temperature) no further temperature change occurs until all the substance has undergone phase change.

Melting Point:-Temperature at which solid and liquid phase are in thermal equilibrium with each other
Boiling point:-Temperature at which liquid and vapour phase are in thermal equilibrium with each other

• Change of phase from solid state to Vapour state without passing through liquid state is called sublimation for e.g Dry Ice and Iodine sublimes.

10. Latent Heat:
• The amount of heat per unit mass that must be transfered as heat when a sample completely undergoes phase change is called latent Heat of the substance for the process.
• Thus when a sample of mass m completely undergoes phase change,the total energy transfered is
Q=Lm
where,
L- Latent heat and is characterstics of a substance
• Its unit is JKg-1.
• Latent Heat for a solid liquid change is called Latent Heat of Fusion Lf.
• Latent Heat for a liquid gas change is called Latent Heat of Vaporisation Lv.