Constant pressure process | Isobaric process

A constant pressure process is also called the isobaric process is one type of thermodynamic process during the pressure stays constant. The term isochoric is derived from the Greek word 'ISO' means constant or equal and 'BAR' means pressure. 

What is the constant pressure isobaric process?

When the gas is heated at constant pressure, it raises its temperature and volume. Since there is a change in its volume the heat supplied is utilized in increasing the internal energy and also doing some external work. This process is governed by Charle's Law. 

Thus, Isochoric process is one in which 

∆P =  0 

Example of Isobaric process: 

The heating of water in an open vessel and the expansion of a gas in a cylinder with a freely moving piston is an example of this process. 

Theoretical explanation:

PV diagram for an Isobaric process

Now, from the above figure m kg of gas is heated at constant pressure from an initial temperature T1 to final temperature T2. This process is represented in the P-V diagram in the above figure. 

Now, we also know that increase in internal energy, 

U₂-U₁ = m Cv ( T₂-T₁)

So, heat supplied Q_1-2 = (U2 - U1) = m Cp (T2 - T1)

Therefore, Pressure volume work is done by a closed system W = ∫ P dv = 0

Work is done by the gas during process, 

W_1-2 = Area below line A-B = p (V2 - V1) = m R (T2 - T1)

This same process we explained when the gas is cooled at constant pressure, there will be a compression. 

So, heat rejected Q_1-2 = (U1-U2) = m Cp (T1-T2)

Work done during the process on the gas

W_1-2 = p (V1 - V2) = m R (T1 - T2)

Notes: 

1. During the expansion OR heating process work is done by the gas is positive. 
2. During the compression OR cooling process work is done on the gas is negative.