States of matter
In everyday life, there are three The three forms in which a substance can exist (solid, liquid, and gas). - solids, liquids and gases. The differences between the three states are due to the arrangement and spacing of the particles, and their motion.
Solids, liquids and gases
The particles in a solid:
- are in a regular arrangement
- vibrate about a fixed position
- sit very closely together
The particles in a liquid:
- are randomly arranged
- move around each other
- sit close together
The particles in a gas:
- are randomly arranged
- move quickly in all directions
- are far apart
Changing state
Transferring The capacity for doing work. to or from a substance can change its state. Heating a substance in the solid state will cause it to The process that occurs when a solid turns into a liquid when it is heated., which changes it to the liquid state. Continued heating will cause the substance to The process in which a liquid changes state and turns into a gas. or boil, which changes it to the gas state.
Some substances in the solid state can change straight to the gas state. This process is called When a solid turns straight into a gas on heating, without becoming a liquid first - or when a gas turns straight into a solid, without becoming a liquid..
A substance in the gas state A change of state in which gas becomes liquid by cooling. when it is cooled, which changes it to the liquid state. Continued cooling causes it to A change of state in which liquid becomes solid by cooling., which changes it to the solid state.
Evaporation and boiling
During evaporation, particles with enough energy can escape the liquid as a gas. Unless energy is transferred from the surroundings by heating, the liquid gradually becomes colder. Boiling happens when enough energy is transferred that the substance evaporates as fast as it can.
Conservation of mass
The number of particles does not change during a change of state, only their spacing and arrangement. As a result, the total mass has not changed. It does not matter if a substance melts, freezes, boils, evaporates, condenses or sublimates - the mass does not change.
These changes in state are called physical changes because the process can be reversed. For example, ice is water in the solid state:
- ice melts to form water in the liquid state when it is heated
- water in the liquid state becomes ice when it is cooled down
This is different from the changes seen in a chemical reaction, when the changes cannot be reversed so easily.