Question

# For hydrogen gas, Z is greater than unity at all pressure.If true enter 1, else enter 0.(A) 1(B) 0

Hint: Z is the compressibility factor of a gas and it can be expressed in terms of formula as: $Z=\dfrac{PV}{nRT}$ .
The value of Z will depend upon the intermolecular forces acting between the gas molecules.

- The ratio of actual volume of any gas at certain temperature and pressure to the ideal volume of that gas in the same conditions is shown by Z and it is called the compressibility factor. It can be given as $Z=\dfrac{PV}{nRT}$
- For ideal gas, Z is equal to 1 and for a real gas, Z is not equal to one.
- When Z > 1, the gas is said to show negative deviation. This implies that the gas is more compressible than expected from ideal behaviour.
- When Z < 1, the gas is said to show positive deviation. This implies that the gas is less compressible than expected from ideal behaviour.
- Now, H and He have very small masses so that attraction forces between the particles of gas are very less. So, the repulsive forces acting between them overcome the attracting forces and as a result, the actual volume of the gas becomes something more than the ideal value.
- It is seen that Z is greater than one for hydrogen and helium at all pressure and it increases with increase in pressure.
- At the same temperature and pressure, the extent of deviation depends upon the nature of gas.
Therefore, from above we can conclude that the given statement is true and option A is the correct option for the given question.

Note: Remember that only hydrogen and helium gas show compressibility factor value more than 1 at every pressure value. It is not true in case of other gases because no other gases will have smaller mass as compared to hydrogen and helium.