Question

P-V plots for two gases during adibatic processes are shown in the following figure. Plots 1 and 2 should correspond respectively to:

• A. $He$ and $O_2$
• B. $O_2$ and $He$
• C. $He$ and $Ar$
• D. $O_2$ and $N_2$

Answer 1

The correct option is B $O_2$ and $He$

We know, for an adiabatic process, $P{V}^{\gamma }$ = constant
where $\gamma$ = poisson's ratio = $\frac{C_p}{C_v}$
$\gamma$ for a monoatomic gas = $\frac{5}{3}$
$\gamma$ for a diatomic gas = $\frac{7}{5}$
So, $\gamma$ for a diatomic gas is less than that of monoatomic gas
Now, slope of adiabatic curve is $-\gamma P/V$
Higher $\gamma$ implies greater slope.
Hence, curve 1 is for diatomic gas ($O_2$) and curve 2 is for monoatomic gas ($He$).