Question

The gases which strictly follow the general equation $(PV=nRT)$ are called ideal or perfect gases. Actually, there is no gas which is perfect or ideal. A real gas is one which actually exists, whether it obeys gas laws strictly or not. Under ordinary conditions, only those gases nearly behave as ideal or perfect which have very low boiling points such as nitrogen, hydrogen, etc. The most easily liquefiable and highly soluble gases such as ammonia, carbon dioxide, sulphur dioxide show large deviations.
A very convenient method of studying deviation of real gases from ideal behaviour is through a compressibility factor $\left(Z\right)$.
$Z=\frac{PV}{nRT}$
(i) $Z=1$, for ideal gases.
(ii) $Z\ne 1$, for real gases.

Consider the equation $Z=\frac{PV}{nRT}$; which of the following statements is correct?

• A. When $Z>1$, real gases are easier to compress than the ideal gas
• B. When $Z=1$, real gases get compressed easily
• C. When $Z>1$, real gases are difficult to compress
• D. When $Z=1$, real gases are difficult to compress

Answer 1

Answer: (C)

When $Z>1$, real gases are difficult to compress

When Z>1, real gases are difficult to compress. This is because the gas shows positive deviation from ideal behaviour.

The option $C$ is the correct statement.