For of a real gas obeying the van der Waals equation, under conditions of low pressure and moderate — States of Matter and Gaseous State Chemistry Question

💡 Solution & Explanation

At low pressure, volume $V_m$ is large, making excluded volume '$b$' negligible ($V_m - b \approx V_m$). The equation $(P + a/V_m^2)V_m = RT$ rearranges to $P = RT/V_m - a/V_m^2$. Multiplying by $V_m/RT$ gives $Z = 1 - a/V_mRT$.