# What happens when a solid is heated

### 3.4 Transitions between the physical states

Experiment 1:

A piece of ice is slowly heated. During this process, the solid ice slowly changes into the liquid water. If you measure the temperature, you will notice that it remains constant at 0 ° C as long as there is an ice-water mixture. This temperature is called the melting temperature of the ice.

If the liquid is brought to the boil by heating, then the liquid water changes into a gaseous state and water vapor is produced. If you measure the temperature, you will notice that it remains constant at 100 ° C as long as there is a water-steam mixture. This temperature is called the boiling temperature of the water.
By adding thermal energy (heating), you can achieve the transitions from solid to liquid (melt) and from liquid to gaseous (vaporize).

Water vapor condenses very easily on cold windows and walls. The transition from gaseous to liquid (condensing) is therefore possible by removing thermal energy (cooling).

The transition from liquid to solid (solidification) can also be achieved by freezing water in the freezer compartment by removing heat.

Experiment 2:

Heating iodine (brown-black solid) produces violet vapors (gaseous iodine). The same brown-black solid can be seen on the cooler upper part of the test tube as on the bottom of the test tube.
So if the solid iodine is heated, the transition from solid to liquid cannot be determined; the transition from solid to gaseous (sublimation) takes place immediately through the addition of thermal energy.
In the upper part of the test tube you can only observe the transition from gaseous to solid (resublimate). With the withdrawal of thermal energy, the transition from gaseous to solid takes place immediately.
There are only two states of aggregation for different types of substance: solid and gaseous.
Comment: A physical state only exists for a portion of substance, i.e. for a large number of particles. A single particle cannot exist in different aggregate states.

In summary, the various transitions between aggregate states can be represented as follows:

The following transitions are possible through the supply of heat (heating):
- melt (transition from solid to liquid)
- evaporate (transition from liquid to gaseous)
- sublime (transition from solid to gaseous).

The following transitions are possible through heat extraction (cooling):
- solidify (transition from liquid to solid)
- condense (transition from gaseous to liquid)
- resublimate (transition from gaseous to solid).

His knowledge of the particle model of matter can be checked further:
3.5 Particle Model of Matter: Exercises