What is an isobaric process?

An isobaric process is one in which the pressure of the gas remains constant throughout. Common examples include heating a gas in a cylinder with a freely moving piston, or atmospheric-pressure phase changes.

Why does temperature affect volume at constant pressure?

At constant pressure, Charles's Law applies: V₁/T₁ = V₂/T₂. When temperature rises, the gas must expand to maintain the same pressure; when temperature falls, it contracts.

What is the difference between monatomic and diatomic gases?

Monatomic gases (noble gases like He, Ar) have only translational kinetic energy: Cv = 1.5R, Cp = 2.5R. Diatomic gases (N₂, O₂, air) also store rotational energy: Cv = 2.5R, Cp = 3.5R. This means diatomic gases absorb more heat for the same temperature rise.

What formulas are used?

Work: W = nR(T₂ − T₁). Internal energy: ΔU = nCvΔT. Heat: Q = nCpΔT. Volumes: V = nRT/P (ideal gas law). R = 8.314 J/(mol·K).

What does a negative result mean?

If T₂ < T₁, the gas is cooled and compressed: W < 0 (work done on gas), ΔU < 0 (internal energy decreases), Q < 0 (heat removed from gas).

Isobaric Process Calculator

Enter moles, temperatures, pressure, and gas type to compute work done, heat transferred, and internal energy change for a constant-pressure process.

Process Inputs

Amount of gas (n) mol

Temperature unit

Initial temperature (T₁) K

Final temperature (T₂) K

Pressure unit

Pressure (P) Pa

Gas type

Cv = 2.5R, Cp = 3.5R

Enter values on the left and click Calculate.

Summary

An isobaric process is a thermodynamic change that occurs at constant pressure. For an ideal gas, the work done equals P ΔV = nR ΔT, the heat transferred is Q = n Cp ΔT, and the change in internal energy is ΔU = n Cv ΔT. This calculator applies the first law of thermodynamics (Q = ΔU + W) to compute all three quantities, along with the initial and final volumes via the ideal gas law.

How it works

Enter the number of moles (n) of the ideal gas.
Set the initial temperature T₁ and final temperature T₂. Choose Kelvin or Celsius — the tool converts automatically.
Enter the constant pressure P in Pascal (Pa) or kilopascal (kPa).
Select the gas type: monatomic (Cv = 1.5R, Cp = 2.5R) or diatomic (Cv = 2.5R, Cp = 3.5R).
The calculator outputs work W, heat Q, internal energy change ΔU, and initial/final volumes using V = nRT/P.
Results update instantly. All outputs are rounded to 4 significant figures.

Use cases

Solving first-law thermodynamics problems at constant pressure.
Calculating heat added to or removed from a gas in an isobaric expansion or compression.
Finding initial and final volumes via Charles's law (V₁/T₁ = V₂/T₂).
Thermodynamics coursework on heat capacity ratios for monatomic and diatomic gases.
Checking work done by a piston in a constant-pressure cylinder.
Comparing energy exchanges in isobaric, isothermal, and adiabatic processes.

Frequently Asked Questions

Last updated: 2026-06-13 · Reviewed by Nham Vu