For an ideal gas, show that at any point on a Clapeyron (p, V) diagram, the absolute value of the slope is greater for an adiabatic process (A) than an isothermal process (I).
For an ideal gas, show that at any point on a Clapeyron (p, V) diagram, the absolute value of the slope is greater for an adiabatic process (A) than an isothermal process (I).
An isothermal process (I) in a Clapeyron diagram is characterised by,
p V ≡ C_I = const where C_I = N R T.
Thus, for an isothermal process,
p = \frac{C_I}{V} and \frac{dp}{dV} = – \frac{C_I}{V^2}= – \frac{NR T}{V} \frac{1}{V} = -\frac{p}{V} .
An adiabatic process (A) in a Clapeyron diagram is characterised by,
p V^γ ≡ C_A = const where C_A = p^{1−γ} (NR T)^γ .
Thus, for an adiabatic process,
p = \frac{C_A}{V^γ} and \frac{dp}{dV} = – \frac{γ C_A}{V^{γ+1}} = – γ \Bigl(\frac{NR T}{pV}\Bigr) ^γ \frac{p}{V} = – γ \frac{p}{V} .
The slopes of both processes are negative in the Clapeyron diagram. Since γ > 1, the absolute value of the slope of the adiabatic process is greater than that of the isothermal process.