How this calculator works
The combined gas law compares two equilibrium states of a fixed amount of ideal gas using absolute pressure and temperature. Process mode also imposes a path constraint and computes work done by the gas, internal energy change and heat added. The initial state determines amount of gas. Heat capacities are assumed constant, with Cv inferred from a supplied ratio Cp/Cv. Adiabatic mode is reversible and quasi-static.
Formula
p1 V1/T1 = p2 V2/T2; n = p1 V1/(R T1); deltaU = n Cv (T2 - T1); Q = deltaU + W_by. Isothermal W = nRT ln(V2/V1); reversible adiabatic pV^gamma is constant.
Worked example
Isothermal expansion from 100 kPa and 0.01 m³ to 0.02 m³ gives 50 kPa and 693.147 J of work. At fixed volume, increasing 300 K to 600 K doubles pressure; with gamma = 1.4 the same initial state gains 2500 J of internal energy.
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Frequently asked questions
Can I enter gauge pressure?
Convert it to absolute pressure first by adding the relevant ambient pressure.
Why is the final-temperature field unused for some processes?
In process mode it applies to isochoric changes. The other processes use final volume and infer final temperature from their path constraint.
Is positive work compression?
Positive work is work done by the gas during expansion. Compression gives negative work under this sign convention.