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Properties of water:
- it is the only substance on Earth that naturally occurs as a solid, a liquid, and a gas. These changes of state require heat exchange which is important to the redistribution of heat energy in the atmosphere
- freezing water molecules causes their mass to occupy a larger volume. Fresh water has a maximum density at around 4° C
- water has a high specific heat, and so it can absorb large amounts of heat energy before it begins to get hot and releases energy slowly when situations cause it to cool. This helps moderate the Earth's climate and helps organisms regulate their body temperature
- water in a pure state has a neutral pH, so is neither acidic nor basic, but changes its pH when substances are dissolved
- water conducts heat more easily than any liquid except mercury. This causes large bodies of water to have a uniform vertical temperature
- water is a universal solvent and is able to dissolve a large number of different chemical compounds. This feature also enables water to carry solvent nutrients in runoff, infiltration, groundwater flow and living organisms
- water has a high surface tension; it tends to form drops and causes water to adhere to vertical surfaces. Its high surface tension allows water and dissolved nutrients to move through plants and blood via tiny vessels in the bodies of some animals
Rain is naturally acidic, with a pH of about 5.6, because it dissolved carbon dioxide and sulfur dioxide.