Question

Positive deviation from ideal behavior takes place because of:
A. molecular interactions between atoms and ${}^{PV}/{}_{nRT} > 1$
B. molecular interactions between atoms and ${}^{PV}/{}_{nRT} < 1$
C. finite size of atoms and ${}^{PV}/{}_{nRT} > 1$
D. finite size of atoms and ${}^{PV}/{}_{nRT} < 1$

Answer 1

Gases have the tendency to deviate from their ideal behavior and can show 2 types of deviation, positive deviation and negative deviation. To explain the behavior of ideal gases, compressibility factor is used. This factor is denoted by z.

Complete answer:
Positive deviation is the characteristic of some ideal gases. The positive deviation from the ideal behavior shows that the gas is less compressible than expected from the ideal behavior of that gas. This less compressibility of the gas is due to the fact of repulsive forces acting between the molecules of the gas. A repulsive force dominates over the attractive forces in the positive deviation of gases.
The compressibility factor z is greater than 1 in the positive deviation, so z > 1 for positive deviation. As the compressibility factor z = $\dfrac{PV}{nRT}$ , so, for positive deviation it becomes ${}^{PV}/{}_{nRT} > 1$.
Hence, Positive deviation from ideal behavior takes place because of molecular interactions between atoms and ${}^{PV}/{}_{nRT} > 1$.

So, option A is correct.

Note:
Positive deviation is shown by hydrogen and helium gases. Negative deviation occurs when attractive forces are strong among the molecules of the gas. This type of deviation has a compressibility factor, z lesser than 1, z < 1. This means that a gas is more compressible. Carbon monoxide and methane gases show negative deviations.