A change of state happens when a material is heated or cooled. Melting turns a solid into a liquid. Freezing turns a liquid into a solid. Evaporating turns a liquid into a gas, like puddles drying in the sun. Condensing turns a gas back into a liquid, like water drops forming on a cold window.
Each material changes state at its own temperature. Pure water melts at 0 °C and boils at 100 °C. When something melts, freezes or evaporates, its weight stays the same: the particles are rearranged, not destroyed. Ten grams of ice make ten grams of water.
Worked example
A puddle is 200 g of water in the morning and gone by the afternoon. Where did the water go?
- The sun warmed the water.
- The water evaporated and became water vapour, a gas.
Answer:The 200 g of water is now in the air, not destroyed.
Key words
- evaporate
- change from liquid to gas
- condense
- change from gas to liquid
- boiling point
- the temperature at which a liquid boils (water: 100 °C)
- melting point
- the temperature at which a solid melts (ice: 0 °C)
- water vapour
- water as a gas
New questions every time.
NGSS-referenced: 5-PS1-2