Water is the most common liquid found on Earth. Pure water is tasteless, colorless, transparent, and odorless. Water is matter because it has mass and occupies space.
States of water
Water can be found in three interchangeable states.
- Solid state – Ice, snow, frost.
- Liquid state – Water in a cup, river, pond, lake, ocean.
- Gaseous state – Water vapor, steam.
Plasma state – A recent study has revealed that water has an entirely new state when it heated to a temperature between 40°C to 60°C
The three states are interchangeable
When the physical conditions of matter are altered, it changes from one phase to another.
Water changes from one state to another by gaining or losing heat. When heat, which is a form of energy, is applied, the particles become active or start bouncing. When the amount of heat energy is enough to enable particles to escape, water turns into its gaseous form.
Melting (Solid to liquid):
When the temperature is 0°C, ice melts into water. This temperature at which ice melts is called its melting point.
However, this heat gain only pushes the molecules away from each other and does not change the temperature of ice. So ice will be at 0°C till it completely melts into water.
Boiling (Liquid to gas):
Boiling is the process in which liquid water is converted into gaseous steam/ vapor by heat gain. Water boils at 100°C to change into vapor and this is called its boiling point.
Steam or water vapor is invisible. When vapor cools (condenses), vapor turns into water droplets and becomes visible as white clouds that are often mistakenly called as steam.
While boiling, water gains heat but this heat is used to move water particles away from each other to form vapor. The temperature of the water will remain at 100°C till all the water has evaporated.
Evaporation (Liquid to gas):
Evaporation is the process in which a liquid is converted into gas at any temperature below its boiling point.
Examples of evaporation – Water poured on the floor evaporates, wet laundry dries when hung.
The speed at which evaporation happens is called rate of evaporation. This is affected by various factors like the temperature of the surrounding, humidity in the surrounding air, the presence/ absence of wind, and area of the exposed surface.
- If the temperature of the surrounding is hot, liquids evaporate faster.
- Strong winds blow away the evaporated water vapor creating more space for further evaporation.
- Water that is poured into a wide vessel will evaporate faster than the same amount of water that has been poured into a narrower vessel.
- If the humidity of the surrounding is higher, then evaporation will be slower.
When water evaporates, it gains heat and cools the surrounding. That is why we feel cool when sweat evaporates from the skin. This process is called evaporative cooling.
Condensation (Gas to liquid):
It is the process in which water vapor and steam change from their gaseous state to become a liquid. Steam is formed when water is boiled to 100°C. When this steam comes in contact with a cooler surface, steam gets condensed to water.
Water vapor in the atmosphere, on contact with this cold bottle, have condensed into water droplets.
Freezing/ solidification (Liquid to solid):
The temperature at which liquid water changes into solid ice is called the freezing point. This happens when water is chilled to 0°C.
Contrary to what is observed in other liquids, when water freezes into ice, water expands. So ice occupies slightly more space than water. This is why ice cubes float on water.