Question

What causes water’s low vapor pressure?

Answer 1

To understand this, we should first know what is vapor pressure. It is one of the most important colligative properties of any liquid. The vapor pressure is the pressure exerted by the vapors over the surface of any liquid at the stage of equilibrium in a closed container.

Complete answer:
Now talking about the water we know that water consists of an O-H polar bond where oxygen possesses a high negative charge whereas hydrogen contains a positive charge which creates a strong type of force known as dipole-dipole force and the bond formed due to this force is hydrogen bond. Hydrogen bonding is the strongest electrostatic force developed due to the difference in the electronegative atoms. This property makes water a unique liquid. The hydrogen bonding is the reason for the lower vapor pressure of water because a very less amount of water particles are allowed to escape the surface which is converted into vapors. This property gives an advantage to the large water bodies, as the water in lakes or oceans does not evaporate easily.

Note:
There are certain factors on which this colligative property depends like the temperature or mixing of any other liquid but one of the most important is the nature of the liquid or its intermolecular forces. If a liquid consists of weak intermolecular forces like van der Waal forces, it will have high vapor pressure which means it will evaporate easily but if the liquid possesses strong intermolecular forces like ion-dipole or hydrogen bonding it will have low vapor pressure i.e the escaping tendency of the particles of that liquid will be very less.