BOILING

Evaporation within the whole mass of liquid is called boiling. At which temperature boiling takes place is called boiling point.
Boiling point increases on adding impurity.
At 574.25 degree, the fahrenheit and kelvin scales read the same.

MELTING

The change of state from solid to liquid is known as melting. The temperature at which the solid and liquid states of the substances are in thermal equilibrium is called melting point.
The solid which expands on heating, their melting point increases with increase in pressure.
Melting point decreases on adding impurity.
Specific heat at boiling point and melting point is infinite.

SPECIFIC HEAT

The amount of heat required to raise the temperature of 1 g of a substance by 1 degree C is called the specific heat of gas.
It is represented by C. Its unit is cal/g degree C or joule/g degree C.

There are two specific heat of gases;

i) Specific heat at constant volume: At constant volume, the amount of heat required to raise the temperature of 1 g of a gas by 1 degree Celsius is called specific heat of constant volume.

ii) Specific heat at constant pressure : At constant pressure, the amount of heat required to raise the temperature of 1 g of a gas by 1 degree Celsius is called specific heat of constant pressure.

CALORIES

Amount of heat required to raise the temperature of 1 g of water by 1 degree C is called 1 cal or amount of heat required to raise the temperature of 1 g of water from 14.5 degree C to 15.5 degree C is called 1 calorie. It is also called international calorie.

1 calorie = 4.2 joule

MERCURY IS PREFERRED IN THERMOMETERS ?

Coefficient of real expansion of mercury is low and uniform.
- mercury has low specific heat.
- mercury does not wet the walls of capillary.
- mercury is a shining liquid and it can be obtained in pure form.
- thermal conductivity of mercury is low and its vapour pressure is also low.

GAS THERMOMETERS PREFERED TO LIQUID THERMOMETER ?

Gas thermometers are preferred over liquid thermometers because;

- gas expands more than liquid, hence gas thermometers are more sensitive than liquid thermometers.
- in a single thermometer different gases can be used.
- all the gases have same cubical expansion coefficient.
- little impurity in the gases has little effect on the temperature being measured.

TEMPERATURE RANGES OF DIFFERENT THERMOMETERS

i) Mercury thermometer from -30 degree C to 357 degree C.
ii) Gas thermometer from - 268 degree C to 1500 degree C.
iii) Platinum resistance thermometer - 200 degree C to 1200 degree C.
iv) Thermocouple thermometer -200 degree C to 1600 degree C.
v) The clinical thermometer reads from 96 degree F to 110 degree F.