Question

Why hydrogen and helium show positive deviation from ideal gas behaviour?

Answer 1

Ideal gases we say that they obey ideal gas equation perfectly.

Ideal gas equation is PV= nRT

where P is the pressure, V is volume, R is the gas constant and T is the Temperature.

But normally in the real gas equation, we introduce Z which is the compressibility factor.

So if Z is grater that 1 then the gas shows positive deviation.

if Z is less than 1 the it shows negative deviation.

and thus we can conclude that the compressibility factor of helium and hydrogen is greater than 1 hence showing positive deviation.