Particles and state changes

Remember how the particles are arranged and move in solids, liquids and gases. (If not, have a look at the Particle Model Revision Bite.) Particles in a solid Particles in a liquid Particles in a gas When heat energy is supplied to a substance, its particles are able to move faster. If enough energy is supplied, the bonds between particles may break, allowing a change of state. Melting The particles in a solid have strong forces attracting them to each other, called bonds. When heat is supplied to a solid, its particles vibrate faster and faster, and the solid warms up. At the melting point, the heat supplied is enough to break some of the bonds. The particles can begin to move around each other and the solid melts. Substances with very strong bonds have very high melting points. Boiling When heat is supplied to a liquid, its particles move around each other faster and faster, and the liquid warms up. At the boiling point, the heat supplied is enough to break all of the bonds. The particles become free to move quickly in all directions and the liquid boils. Substances with very strong bonds have very high boiling points. Evaporation Boiling happens all through a liquid but evaporation happens at its surface. Evaporation is the reason why wet clothes on a washing line dry, even though the temperature is below the boiling point of water. In a liquid, some of the particles have more energy than the others. Some of them may have enough energy to break their bonds and escape from the surface of the liquid as a gas. The remaining liquid becomes slightly colder because the particles with less energy are left behind - try licking the back of your hand and blowing across it gently to show this for yourself. Evaporation happens faster when the liquid is hotter. When the liquid is at its boiling point, the evaporation is happening as fast as it can.