In the previous section, our study was focused on matter, its composition and how it is made and some of its properties. The next section will focus on the changes that matter can undergo.

We live in an environment where many and different processes or phenomena take place. Those processes can be put into different categories: physical, chemical, biological, etc. In our study here, we’ll be interested in two main categories of processes:

(i) Physical processes

(ii) Chemical processes

Questions:

  1. What’s the difference between physical processes and chemical processes? Give examples to illustrate.
  2. What are the factors or driving forces behind the changes of matter?

Solution:

1.

Differences between physical phenomena, also called physical processes, and chemical phenomena or chemical processes. Physical phenomena, physical processes or physical changes are changes that affect the physical properties of the matter, but not the nature of matter.

Examples:

  • Changes of states of matter: vaporization and condensation of water.
  • Mixing alcohol and water.

Chemical phenomena, chemical processes or chemical changes are changes that affect the nature of matter and change it into another matter.

Examples:

  • Burning wood produces carbon dioxide, water, carbon and energy.
  • Heating limestone at high temperature forms quicklime and carbon dioxide.
  • Rusting of a metal such as iron in air forms rust.

2.

The factors or driving forces behind the changes of matter are:

Energy:

  • Internal energy: energy stocked in matter, attraction and repulsion forces between particle of the matter.
  • External energy supplied or applied to the matter.

Entropy:

Widely defined as a measure of disorder, randomness or probability (possibilities) of organization of matter.

Imagine students on the playground for their break. Are you going to find them organized in a certain order such as by size, alphabetical names, by gender, etc.? The most naturally probable situation you are going to find them on the playground is in disorder, randomly organized i.e. the least organized situation.

That is the same in nature, things in nature tend to be disorganized and that is the most probable natural situation. In a chemical reaction, the increase of the entropy(s) plays in favor of the reaction.

Another example, take a sugar cube, it is well organized, each molecule has its place and surrounded by a certain number of neighboring molecules. This structure has a low entropy. The probability of having that organization naturally is almost zero. On the other side, if this sugar cube is dissolved in water, molecules are separated and spread randomly in water and the entropy is high.

- Randomness is natural and more probable: high entropy.

- Orderliness is not natural, hence less probable: low entropy.