Lesson 7 of 15

Adiabatic Process

Adiabatic Process

In an adiabatic process, no heat is exchanged with the surroundings (Q=0Q = 0). From the First Law of Thermodynamics:

ΔU=QW=W\Delta U = Q - W = -W

Any work done by the gas comes entirely at the expense of its internal energy, so the temperature changes.

Adiabatic Relations for an Ideal Gas

The ratio of heat capacities γ=Cp/Cv\gamma = C_p / C_v governs adiabatic behaviour. Two useful relations:

Temperature–volume: TVγ1=const    T2=T1 ⁣(V1V2) ⁣γ1TV^{\gamma-1} = \text{const} \implies T_2 = T_1\!\left(\frac{V_1}{V_2}\right)^{\!\gamma-1}

Pressure–volume: PVγ=const    P2=P1 ⁣(V1V2) ⁣γPV^{\gamma} = \text{const} \implies P_2 = P_1\!\left(\frac{V_1}{V_2}\right)^{\!\gamma}

Work Done by the Gas

Since Q=0Q = 0, the work equals the drop in internal energy:

W=P1V1P2V2γ1=nR(T1T2)γ1W = \frac{P_1 V_1 - P_2 V_2}{\gamma - 1} = \frac{nR(T_1 - T_2)}{\gamma - 1}

Heat Capacity Ratios

Gas typeExampleγ\gammaCvC_v
MonatomicHe, Ar5/31.6675/3 \approx 1.66732R\tfrac{3}{2}R
DiatomicN₂, O₂, air1.41.452R\tfrac{5}{2}R

Your Task

Implement the two functions below.

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