Heat and Thermodynamics

Heat --Heat is a Energy which is transferred between system and the surroundings to the temperature Difference Unit of heat is called cal it is defined as the amount of heat required to raise the temperature of 1 gram of water through 1°C


Specific Heat Capacity

It is the quantity of heat in cal required to raise the temperature of 1 gram of substance by 1 degree Celsius

The quantity of heat required to change the temperature of a body of mass m by∆T is proportional to the product of mass and change in temperature

Q=ms∆T

The  product of the mass of the body and the specific heat capacity is called heat capacity it is defined as the amount of heat required to raise the temperature of a body by 1 degree Celsius

Principle of calorimetry

Two bodies of masses M1 and M2 specific heat S1 and S2 and at the temperature t1 and t2 are brought in contact with each other as you t1 is greater than t2 and heat will flow from the body 1 to body 2 if T is the common temperature of the two bodies at the state of thermal equilibrium

Heat lost by body = Heat gained by body 

MS(t1-T)= ms(T-t2)


Kinetic theory of gases state

An ideal gas or perfect gas is that gas which is strictly always a gas laws such as Boyles law , Charles law at all the values of temperature and pressure

Boyles law --

It states that for a given mass of an ideal gas at constant temperature the volume of gas is inversely proportional to its pressure

P1V1=p2V2

Charles Law -- 

It is stated that for a given mass of an ideal gas at constant pressure the volume of a gas is directly proportional to its absolute temperature

V1/T1=V2/T2

Gay -Lussac Law --

It states that for a given mass of an ideal gas at constant volume pressure of a gas is directly proportional to its absolute temperature

P1/T1=p2/T2

Ideal Gas Equation--

PV=nRT 


Kinetic theory of gases

Kinetic theory of gases is based on the following assumptions

1) The molecules of a gas are a small particles and they are very far apart in comparison to their sizes


2) The total volume of the molecules is negligible as compared to the size of a gas


3) The molecules collide elastically with each other


4) The molecules exert no force on each other except during collisions


Relationship between

 pressure and the kinetic energy of the gas

Pressure = 2/3KE 

Absolute temperature and mean square velocity

Absolute temperature of an ideal gas is directly proportional to mean square velocity of its molecule

    v= √T

Various speeds of gas molecules

RMS speed of a gas molecule

Square root of mean of the squares of the speed of a gas molecule is called their root mean square speed

v = ✓ 3RT/m

Average speed

It is the arithmetic mean of the speed of the molecule in a gas

v = ✓8kT/πm

Most probable speed

It is defined as the speed which is possessed by maximum fraction of total number of molecules of a gas

v = ✓2kT/ m

Degree of freedom--


It represents the number of independent possible ways in which the system can have the energy due to its motion or the configuration


1) for ideal monoatomic gas degree of freedom is 3 due to translational motion in three directions


2) for ideal diatomic gas degree of freedom is five due to three translational and two rotational motion



Mon Nov 28, 2022

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