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Melting and Freezing

Ice can form across the top of a lake when the water freezes but there is usually still liquid water beneath. Some people go swimming in the freezing water for fun!
Ice can form across the top of a lake when the water freezes but there is usually still liquid water beneath. Some people go swimming in the freezing water for fun!
Credit: Wikimedia Commons. Click here for the license
Liquid cream is mixed with other ingredients to give it flavour and colour and then frozen to make solid ice cream
Liquid cream is mixed with other ingredients to give it flavour and colour and then frozen to make solid ice cream
Credit: Wikimedia Commons. Click here for the license
If its warm, ice cream can melt and become liquid again.
If its warm, ice cream can melt and become liquid again.
Credit: Wikimedia Commons. Click here for the license
Even rock melts if it gets hot enough! Volcanoes can erupt and spit out molten rock as 'lava'.
Even rock melts if it gets hot enough! Volcanoes can erupt and spit out molten rock as 'lava'.
Credit: Wikimedia Commons. Click here for the license

When you heat a solid, it can melt into a liquid. When you cool a liquid, it can freeze into a solid.

Melting: Ice (solid) turns into water (liquid).

Freezing: Water (liquid) turns into ice (solid).

The temperature where this happens for water is 0°C.

This process of changing state is all about energy. Adding heat energy makes the tiny particles in a solid wiggle faster until they break free, but taking energy away (cooling) makes them slow down and lock back into place.

Different solids have different melting points. An ice cube melts at 0°C, but a solid chocolate bar melts at a warmer temperature (which is why it melts in your hand!), and solid rock needs the incredible heat of a volcano to melt into lava.

💡 Fun Facts

  • Chocolate and butter are solids that melt easily when heated, which is why they are great for baking.
  • In winter, water in ponds and puddles can freeze to form a solid layer of ice on top.
  • Volcanoes shoot out hot, liquid rock called lava, which cools down (freezes) to become solid rock.
  • We call 0°C the freezing point of water, but it's also its melting point!
  • Water is special: when it freezes into ice, it actually expands (gets bigger). This is why a full, sealed plastic bottle can crack or split open if you leave it in the freezer.
  • Snow and hail are solid forms of water. If they fall through air that is warmer than 0°C, they melt on the way down and land as rain. ❄️➡️🌧️
  • Even solid metals can melt. Blacksmiths heat iron until it becomes a glowing liquid, then pour it into a mould (a shape) and let it freeze back into a solid, like a horseshoe or a sword.
  • Glass is made by melting sand (a solid) at a very high temperature (about 1700°C) into a thick, syrupy liquid, which is then shaped and cooled.