Unit 11:  Heat and temperature                                    1   2   3   4   5   6

1. The thermal energy

The inside of a substance (solid, liquid or gas) is never at rest.

- The atoms or molecules in solids vibrate a little,but they can't move around.

- The atoms or molecules in liquids vibrateand they can also move around

   but keeping the distances between them.

- The atoms or molecules in gases move around freely:their movements

   are constant and random.

As the temperature increases, a body changes from a solid state to a liquid state,

and finally from a liquid state to a gas state. So, we can say that temperature is linked to the movement of the different particles (atoms and molecules) that make up substances.

All particles have a certain amount of kinetic energy (or internal energy)

due to the fact that they move: this energy increases as the temperature increases.

However, because a small amount of matter can contain thousands of billions or even trillions of particles, it is more precise to talk about the average kinetic energy of the particles or their thermal energy.

Thermal energy is the average kinetic energy of a very large group of atoms or molecules.

1.1. When has a liter of water more internal energy when it is at 50ºC or when it is at 90ºC? Why?