Heat is defined as the sum of kinetic energy contained by the molecules of that object. The SI unit of heat is Joules. In c.g.s system it is measured calorie.

1calorie= 4.2joules


Heat depends on mass of the object and average kinetic energy of the molecules.

Heat is directly proportional to the mass of object and average kinetic energy.


Effects of heat are:

a. It changes the state of matter

b. It changes the temperature of an object.

c. It changes the solubility of a substance.

d. It changes the size of an object.

e. It changes the color of the body.

f. It changes the volume of the body


Temperature: Temperature is the degree of hotness or coldness of an object. Temperature is the thermal condition of the body that determines rate of flow of heat from one body to another. It is the average kinetic energy of the molecule.


Temperature scale

Centigrade scale:

Lower fixed point: 00C

Upper fixed point: 1000C

Fahrenheit scale:

Lower fixed point: 320F

Upper fixed point: 2120F

Kelvin scale:

Lower fixed point: 273K

Upper fixed point: 373K


Anomalous expansion of water:

Generally all substance expands on heating and contracts on cooling. But in case of water the behavior is different, when water at 0c is heated its volume decrease up to 4 and density increases. At 4c the density becomes maximum and beyond this temperature volume start to increase. Thisunusual expansion of water is called anomalous of water.

Heat equation:

The amount of heat gained or lost by a body is equal to the product of the mass (m), the specific heat capacity (s) and the change in temperature (dt) of that body is called heat equation.

Q= msdt


Let us consider the temperature of the body changes to t1 to t2 when it is heated and m be mass of the body then, change in temperature dt = t2 – t1

If Q is amount of heat supplied then, Q ……….m……..1


Then combining 1 and 2 we get Q=msdt………3

Where s is proportionality constant called the specific heat capacity of the material of the body which is constant for the given material and independent of the shape size and mass of the body.


Principle of calorimetry:

When two body of different temperature are kept in thermal contact, heat transfers takes place from the hot body to cold body and the process continues until the equilibrium (same temperature) state is maintained. This principle works on the principle of the conservation of energy.

Heat lost = Heat gained


Specific heat Capacity:

The amount of heat required to change the temperature of a body of unit mass by 1°C is known as specific heat capacity of that body.

Or s = Q/mdt

S.I unit of specific heat capacity is J/kg°C


Body having he more heat capacity changes the temperature slowly then the body having less heat capacity.

Specific heat capacity of water (s) = 4200 J/kg°C means 4200J of energy is needed to raise the temperature through 10C