= Solution
For the given one-mole model,
$$
p=\frac{RT}{V-b},\qquad V>b.
$$
At fixed positive <temperature> its <isotherm> is an ideal-gas hyperbola shifted right by $b$: <pressure> diverges as $V\to b^+$ and tends to zero as $V\to\infty$. Higher <temperatures> give higher <pressure> at any fixed allowed <volume (thermodynamics)>.
\Image[/past-exam-of-the-physics-b-course-of-the-university-of-cambridge/2017/paper-2-2017-excluded-volume-isotherms.png]
{title=Pressure-volume isotherms for the excluded-volume ideal gas}
{description=Original dimensionless isotherms with a common vertical asymptote at V=b. They are monotonically decreasing and have no coexistence plateau or critical inflection.}
For positive $b$, the <volume (thermodynamics)> $V-b$ is the effective <volume (thermodynamics)> available to molecular motion. Thus $b$ describes excluded-volume repulsion or an effective incompressible molecular core. It is a molar <volume (thermodynamics)> in this one-mole equation, not necessarily the literal sum of molecular geometric <volume (thermodynamics)>. Setting $b=0$ recovers the <ideal gas law>. No attractive-energy term is included.
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