Hydrogen () and Helium () gases experimentally show a positive deviation () from ideal behavior even — States of Matter and Gaseous State Chemistry Question

💡 Solution & Explanation

For $H_2$ and $He$, the intermolecular forces of attraction are virtually non-existent, meaning their van der Waals constant '$a$' is extremely small. Therefore, the term $a/V^2$ is negligible at normal temperatures. The equation becomes $P(V-nb) = nRT$, leading to $Z = 1 + Pb/RT$. Thus, repulsive forces (size effect '$b$') dominate, and $Z > 1$ at all pressures.