Depending on the temperature, a substance can exist as a solid, liquid or gas.
For example, at room temperature, water is a liquid. However, when heated, it turns into water vapour, which is a gas. When water is put in a freezer, the temperature decreases, so it turns into ice, which is a solid.
Physical changes do not alter the nature of the particles themselves; rather, they affect the particles’ arrangement and movement.
Matter can change between states, and there are five different types of state changes, which you can see below.
Melting: This is the process that changes a solid to a liquid. When a solid is heated, the particles begin to vibrate as they gain more energy. This causes the forces between the particles to become weak.
Boiling: Otherwise known as vaporisation, this process changes a liquid to a gas. As mentioned, adding heat to a liquid will cause the particles to vibrate and move around even more. This also causes the bonds between the particles to break, forming a gas.
Condensation: This process changes a gas to a liquid. To go from a gas to a liquid, the gas needs to be cooled. This causes bonds to form between the particles, which leads to liquid formation.
Freezing: This process changes a liquid to a solid. To freeze a liquid, you’ll need to cool it down, which leads to the formation of bonds between particles.
Sublimation: Under certain conditions, a solid can turn into a gas. An example of this is the sublimation of iodine.
When iodine crystals are heated, they turn into purple iodine gas. This is an example of sublimation because iodine changes directly from a solid to a gas.
Pure substances, which are substances made out of only one element, have exact melting and boiling points. The table below shows the melting and boiling points for some pure substances.
|Element||Melting Point (°C)||Boiling Point (°C)|
When you look at tables of melting and boiling points online, you’ll notice that freezing and condensation points are not listed. This is because the melting point for a substance is the same as the freezing point and the boiling point for a substance is the same as the condensation point.
For example, look at oxygen in the table above. If you cool oxygen to -183°C (the boiling point), oxygen becomes a liquid and if you cool oxygen further to -219°C then oxygen becomes solid.