Chapter 9 Properties of Water

Water Cycle (Hydrologic Cycle)

Continuous biogeochemical circulation of water across Earth and its states of matter

Water

A polar inorganic compound defined with the chemical formula “H₂O” and consists of one oxygen atom covalently bonded with two hydrogen atoms

High Melting Point and Boiling Point Reasoning

Water has hydrogen bonding due to its polar covalent structure being bent and asymmetrical with two hydrogen atoms being covalently bonded to an oxygen causing a partial positive charge on the hydrogen and a partial negative charge on the oxygen. These strong intermolecular forces mean water has a high latent heat and specific heat capacity, resulting in a higher melting and boiling point because more thermal energy is required to overcome these hydrogen bonds.

Group 16 Hydrides

Compounds which consist of a group 16 element covalently bonded to two hydrogen atoms.

Trends of Group 16 Hydrides

Water has a relatively high melting and boiling point as hydrogen bonding between water molecules is strong compared to other Group 16 hydrides that undergo dipole-dipole bonding between respective molecules.

Dispersion forces also increase with larger molecules. This explains why H₂Po (a larger molecule) has a slightly higher melting and boiling point than H₂S (a smaller molecule), despite both Group 16 hydrides undergoing the same intermolecular forces between respective molecules.

Potable

Water that is safe to drink

Evaporation

A type of vaporisation which occurs only at the surface of a liquid, relatively slow to boiling

Heat Capacity

The quantity of thermal energy (in joules) required to increase the temperature of an entire object or substance by one celsius or kelvin

Latent Heat of Vaporisation

The amount of energy required to convert 1 mol of a substance from its liquid state to its gaseous state or from a gaseous state to a liquid state at the boiling point of the substance

Latent Heat of Fusion

The amount of energy required to convert 1 mol of a substance from its solid state to its liquid state or from a liquid state to a solid state at the boiling point of the substance

Phase Change

Transition of a substance from one state to another

Desalination

The industrial process of removing salts and minerals from seawater or brackish water to convert it into fresh water for human consumption or irrigation

Specific Heat Capacity

The quantity of thermal energy (in joules) required to increase the temperature of a certain amount (usually one gram) of a substance by one celsius or kelvin

Vaporisation

The phase transition where a substance converts from a liquid or solid state into a gas or vapour