Question

Logarithms of readings of pressure and volume for an ideal gas were plotted on a graph as shown in Figure. By measuring the gradient, It can be shown that the gas may be

• A. monoatomic and undergoing an adiabatic change
• B. monoatomic and undergoing an isothermal change
• C. diatomic and undergoing an adiabatic change
• D. triatomic and undergoing an isothermal change

Answer 1

Answer: (C)

diatomic and undergoing an adiabatic change

Answer 2

The plot of $\log P$ vs $\log V$ for an adiabatic process $PV^\gamma = \text{constant}$ has a slope of $-\gamma$. From the graph, the slope is calculated as $\frac{2.10 - 2.38}{1.30 - 1.10} = -1.4$. Thus, $\gamma = 1.4$. This value corresponds to a diatomic gas ($\gamma = 7/5$). An isothermal process has a slope of $-1$, which is not observed.