ShareChanging Matter - Moving Molecules
Thermal (or heat) energy can be either taken in or given off from substances. The amount of energy that is added or removed molecular changes the molecular motion that is observed. As you learned last year in 7th Integrated Sci-ber Text, the molecule motion determines which phase of matter is observed. Slow moving molecules are found in solids while rapid moving molecules are present in gases. Liquids have molecules in motion that are slower than gases, but much more rapid than a solid.
Increasing the motion of the molecules can get the substance to change phase. If you slow down the molecules in a gas, the substance will change to a liquid. In a similar manner, if you increase the molecular motion of a solid, it will change to a liquid.
Remember that water is found in all three phases here on Earth.
As you look at the photographs above, answer the following questions:
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Check your answers by highlighting the box below.
| 1. Very low energy 2. Gas 3. High energy 4. Solid |
With this in mind, visualize how the atoms or molecules of H2O are moving in each of these cases? As you consider this, think about these questions. Have you ever watched ice move? Does it move fast or slow? Which seems to be moving the fastest - water in a river or steam escaping from a boiling pot of water?
Remember that an increase in the amount of thermal energy will increase the motion of the molecules in the substance. The greater the increase of thermal energy, the greater the motion of the molecules. The amount of thermal energy will determine if the material is a solid, liquid, or gas.
Temperature refers to how hot or cold something is, it is defined as the average value of the kinetic energy of the molecules of a substance. That is why the temperature of a substance is always changing. Heat is flowing into and out of matter all the time.
