Physical changes don’t change the particles-just their arrangement or their energy
* When a solid is heated, its particles gain more energy
* This makes the particles vibrate more, which weakens the forces that hold the solid together
* At a certain temperature, called the melting point the particles have enough energy to break free from their positions, called melting and turns a solid to an liquid
* When a liquid is heated, again the particles get even more energy
* This energy makes the particles move faster, which weakens and breaks the bonds holding the liquid together
* At a certain temperature, called the boiling point, the particles have enough to break their bonds
* This is evaporating, and the liquid becomes a gas
* As a gas cools, the particles no longer have enough energy to overcome the forces of attraction between them
* Bonds form between the particles
* At the boiling point, so many bonds have formed between the gas particles that the gas becomes a liquid, this is called condensing
* When a liquid cools, the particles have less energy so move around less
* There’s not enough energy to overcome the attraction between the particles, so more bonds form between them
* At the melting point, so many bonds have formed between the particles that they’re held in place
* The liquid becomes a solid and this is called freezing
Heating up
Melting - When a solid is heated, it absorbs energy and it melts, turning into a liquid.
Boiling - If the liquid is heated, it absorbs more energy and it boils, turning into a gas.
These changes absorb energy from the surroundings so they are endothermic.
Evaporating is when a liquid turns into a gas slowly, at temperatures that are below its boiling point. Puddles dry up because they evaporate – they don’t boil.
Cooling down
Condensing - If a gas is cooled, it transfers energy to the surroundings, and turns into a liquid.
Freezing - If the liquid is cooled, it transfers energy to the surroundings, and turns into a solid.
These changes transfer energy to the surroundings so they are exothermic.