
An isobaric process is a thermodynamic process in which the pressure of the system remains constant, while volume and temperature may change. The word: Iso in the Greek language means ‘equal’ and “bar” is from baros (weight/pressure), which shows the nature of constant pressure of the system.
Let us understand how the isobaric process happens. Read on to learn its characteristics and equations in detail.
When a system undergoes a process at constant external pressure, it is called an isobaric process.
Q = ΔU + W
In which,
Here is a complete understanding of an isobaric process:
W = P(V₂ − V₁)
→ V₁ is initial volume
→ V₂ is final volume
Q = nCpΔT
→ Cp is the molar heat capacity at constant pressure
ΔU = nCvΔT
In a P–V diagram, an isobaric process is represented as a horizontal line, because pressure remains constant while volume changes. Slope = 0 because pressure is constant.
PV diagram of isobaric process
When a gas in a piston-cylinder arrangement is heated at constant pressure, the piston moves upward, increasing the volume. This is an example of isobaric expansion.
| Property | Details |
|---|---|
| Process type | Isobaric (constant pressure) |
| Pressure | Constant |
| Work done | W = PΔV |
| Heat absorbed | Q = nCpΔT |
| Change in Internal Energy | ΔU = nCvΔT |
| PV diagram | Horizontal line |
| Example | Gas heated in piston-cylinder |
By using the First Law:
Q = ΔU + W
We can substitute the values of:
Q = nCvΔT + PΔV
And also since, PΔV = nRΔT
Q = nCvΔT + nRΔT = nCpΔT
Hence, the Mayer’s relation is proved -
Cp − Cv = R
An isobaric process is one which occurs at constant pressure. Heat when supplied is partly used to raise internal energy and then partly to do work. And when we look at the PV diagram, it is a horizontal line.
Work done in an isobaric process depends on change in volume: W = P(V₂ − V₁)
And we also saw that the heat absorbed by the system → Q = nCpΔT
Q1. What is meant by an isobaric process?
An isobaric process is a thermodynamic process at constant pressure.
Q2. How is work done calculated in an isobaric process?
We use the formula: W = P(V₂ − V₁).
Q3. What is the PV diagram of an isobaric process?
A horizontal line parallel to the volume axis.
Q4. What is an example of an isobaric process?
Heating or cooling of a gas in a piston-cylinder arrangement at constant pressure.
Q5. Why is Cp used in isobaric processes?
Since the heat is supplied at constant pressure, the molar specific heat at constant pressure (Cp) is applicable.
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