Question

Water is liquid at room temperature, the most important reason for this is the:
A. high boiling point of water
B. high melting point of water
C. High heat of vaporization of water
D. Cohesive forces due to hydrogen bonds in water

Answer 1

Hint:A hydrogen bond is a partial intermolecular bonding interaction between a lone pair of electrons present on an electron rich atom and the neighboring hydrogen atom. The electron rich species usually involve the second-row elements such as nitrogen, oxygen, or fluorine and interact with the antibonding molecular orbital of the hydrogen atom. These electron rich species should be highly electronegative as well.

Complete step by step answer:
Due to its high polarity (because of high electronegativity difference), a water molecule in the liquid or solid phase can form up to four hydrogen bonds with the neighboring molecules. Hydrogen bonds are about ten times as strong as the Van der Waals force that attracts molecules to each other in most of the liquids. This is the reason why the melting and boiling points of water are much higher than those of other analogous compounds like hydrogen sulfide. This also explains why water exists in a liquid state at room temperature. Due to the high electronegativity of the oxygen atom present in water, it forms a weak hydrogen bond with the adjacent hydrogen atoms as they are partial positive species.

Thus, the correct option is D. Cohesive forces due to hydrogen bonds in water.

Note: The presence of hydrogen bonds in water also explains its exceptionally high specific heat capacity, heat of fusion, heat of vaporization, and thermal conductivity. These properties make water more effective at moderating Earth's climate, by storing heat and transporting it between the oceans and the atmosphere. The hydrogen bonds of water are around \[23{\text{ }}kJ/mol\] (compared to a covalent \[O - H\] bond at \[492{\text{ }}kJ/mol\] ).