Ice floats on the surface of the water. This should mean that liquid water is denser than ice. Is it the case? Let’s find out.
Is liquid water denser than ice?
Yes, liquid water is denser than ice. The density of ice and water are 0.917 g/cm3 and 0.9998 g/cm3 respectively at 0°C and standard atmospheric pressure( i.e. 101.325 kilopascals). The density of a substance is defined as its mass per unit volume. It is denoted by the symbol ρ.
Density = (mass)/(Volume)
Generally for a substance, if mass does not change its solid form has more density than its liquid form at the same temperature and pressure. But in the case of water (H₂O), liquid water has more density than solid ice. This is because ice crystals are made up of hexagonal crystal lattices which form due to the Hydrogen bonding between molecules of H₂O. The unoccupied spaces are much more in ice crystal than liquid water which reduces its density.
On the contrary, in liquid water, the Hydrogen bonds constantly break and reform. The H2O molecules are relatively close together increasing liquid water’s density.
- During freezing temperatures, when lake or ocean water freezes, ice floats on top. This is because ice is less dense than liquid water. A less dense substance floats on the more dense liquid. This is also the reason why oil floats on water.
- Ice takes up more area than liquid water.
Hydrogen bonds form when a Hydrogen atom forms a molecule with a more electronegative atom. Let’s take the example of H₂O, two Hydrogen atoms and one Oxygen atoms combine to form H₂O. This happens because Oxygen needs 2 electrons and hydrogen needs 1 electron. Oxygen has more affinity for electrons hence it acquires a slight negative charge.
Hydrogen, on the other hand, acquires a slight positive charge. As a result, a hydrogen bond forms between Hydrogen and Oxygen atoms of two different H₂O molecules.
Hydrogen bonds are stronger than Van der Walls forces but weaker than ionic and covalent bonds. These bonds break easily if enough energy is Supplied.