States of Water, and Changes in State

Water occurs in nature as ice or snow, liquid water, or water vapour, which are each in a solid, liquid, or gaseous state. The state of matter is the form that the substance can take. In different states of matter, the arrangement of the particles and their relationships are different, but the substance itself remains the same. Liquid water, water vapour, and ice are all made of water molecules - H₂O.

At 0°C, the state of the water begins to change - the liquid water turns to ice. The change from a liquid state to a solid state is called freezing, and solid substances are called solids.

If you put an ice cube in a glass in a warm room, it will start to melt immediately. A solid melts and becomes a liquid.

If you hang wet laundry to dry, it will dry after a while. This is due to evaporation: water becomes water vapour and disperses into the air. The warmer the air and the windier the weather, the faster the evaporation. The state of water changes as the liquid substance becomes a gas. Water can also change its state from a solid to a gas without turning into a liquid in-between. This happens, for example, when you take your laundry to dry outside in cold weather in winter.

At 100°C, the water starts to boil, and at this temperature, the water evaporates quickly. As the air above the pot is much cooler, the water vapour cools and condenses, meaning that it becomes water droplets. As it condenses, the state of the water changes, the gaseous substance becomes a liquid substance. For the same reason, a mirror or glass becomes hazy when you breathe on it, because when your breath comes in contact with the surface of a cold mirror, it cools, and the water vapour in it condenses into water. Remember that we do not see water vapour. What we see is actually condensed water vapour, or liquid water.