Physics

# Thermodynamics.

## Thermodynamics:

• Branch of physics which deals with the study of relationships involving heat, mechanical work, and other aspects of energy and energy transfer.

## Thermodynamics system:

• It is an assembly of an extremely large number of particles (atoms or molecules) having a certain pressure, volume and temperature.
• It is of two types:

1) Isolated System: (no heat can enter or leave out the system)

2) Closed system: (There can be heat exchange between the system and surrounding) ## Thermal Equilibrium:

• A thermodynamics system is in thermal equilibrium if the temperature of all parts of it is same.

## Zeroth law of Thermodynamics:

• When two bodies A and B are in thermal equilibrium with third body C then the body A and B also must be in thermal equilibrium with each other. ### Work Done:

• Work is said done when volume of gas changes.
• Work done is positive if expansion takes place and is negative if compression takes place.
• Work (W) = PdV
• Area under PV curve between volume axis is equal to work done.
• For a closed cycle, area of closed loop gives work done.
• When P remains constant throughout the expansion, the work done by the gas is

### Internal Energy of a Gas

• The sum of energy due to molecular motion (KE) and due to molecular configuration (PE) is called internal energy of gas Note:

For ideal gas intermolecular force of attraction is neglected i.e. PE=0, so internal energy of ideal gas is KE which is only the function of temperature.