Question

The critical temperature of water is higher than that of ${O_2}$ because the ${H_2}O$ molecule has :
A.fewer electrons than ${O_2}$
B.two covalent bonds
C.V-shape
D.dipole moment

Answer 1

The critical temperature of a substance is defined as the temperature at and above which the vapours of the substance cannot be liquefied , no matter how much pressure we apply . Every substance has a different critical temperature .

Complete step by step answer:
Critical temperature of a gas is that temperature above which it cannot be liquified.

Now, we know that water molecules have a greater dipole moment as compared to ${O_2}$ molecule . Water is a polar molecule as the two electropositive hydrogen atoms are bonded to the electronegative oxygen atom so partial positive and negative charges develop and a dipole moment comes into being.While in the oxygen molecule no charges get developed because the equal and opposite charges of the two oxygen atoms cancel each other's effect.

The dipole moment of ${H_2}O$ molecule is 1.84D while that of ${O_2}$ is 0D.
This means that water molecules have strong intermolecular forces , that is, dipole-dipole forces. Greater the intermolecular forces, higher the critical temperature.

This means water molecules need a much higher temperature to convert into liquid state.
On the other hand, oxygen molecules have a weaker intermolecular force of attraction ( van der Waals forces of attraction ) .That is why it can be liquefied easily hence less temperature is required.
Therefore option D is correct.

Note: Beyond the critical temperature , we cannot distinguish between the two phases , that is , gas and liquid . Also beyond this temperature a gas cannot be liquefied by compression .