Final answer:
Liquid water differs from its gaseous reactants, hydrogen and oxygen, due to hydrogen bonding, which results in water's unique properties, such as high boiling point, surface tension, and the solid state (ice) being less dense than the liquid state.
Step-by-step explanation:
Hydrogen bonding is the key factor that explains why the properties of liquid water (H2O) are different from the properties of its gaseous reactants, hydrogen (H2) and oxygen (O2). When hydrogen and oxygen react to form water, they undergo a chemical reaction where the diatomic molecules of hydrogen and oxygen produce a binary compound with unique properties. Unlike most molecular compounds with a mass similar to water, which are gases at room temperature, the strong hydrogen bonds in water enable it to remain in the liquid state. Water's bent molecular shape allows each molecule to form hydrogen bonds with several other molecules, leading to its high boiling point, surface tension, and ability to act as an excellent solvent.
Water exhibits other remarkable properties when it changes state. For example, during freezing, water molecules form a crystalline structure maintained by hydrogen bonding that makes ice less dense than liquid water. This is unusual because it is common for the solid state of a substance to be denser than the liquid state. Moreover, when water is heated, its molecules gain kinetic energy, leading to the breaking of hydrogen bonds and the transition of water molecules into gas (steam or water vapor).