Why is water in a liquid state at 25 degrees Celsius, while H2S is a gas?

The answer is grounded in the nature of intermolecular forces. Water (H2O) exhibits strong hydrogen bonding due to its polar nature and the presence of highly electronegative oxygen atoms. These hydrogen bonds occur between the hydrogen atoms of one water molecule and the oxygen atoms of adjacent molecules, leading to a relatively high boiling point and allowing water to remain in a liquid state at moderate temperatures like 25 degrees Celsius.

In contrast, hydrogen sulfide (H2S) has weaker van der Waals forces (specifically dipole-dipole interactions and London dispersion forces) since the sulfur atom is less electronegative compared to oxygen. Consequently, H2S does not form hydrogen bonds as effectively as water, resulting in a lower boiling point and the ability to exist as a gas at room temperature.

Therefore, the presence of stronger intermolecular bonds in water is the reason it remains liquid at 25 degrees Celsius while H2S is in a gaseous state.