Types of Change and Separation

Introduction

Up to now we have dealt with observations of single static items. Now, let's take a look at change. The reason for dealing with change is, of course, that without change there wouldn't be any chemistry. There wouldn't be things happening that we could observe. In fact, without change we wouldn't be able to observe.

First we will consider what we call physical changes. After that we will consider what we call chemical changes. The distinction between these two types of change lies in answering this question. Does the observed change result from a change in condition of the same material or from a new material with different properties than the material you started with?

More examples will follow, but let me give you one of each for now. If you evaporate gasoline, there is a change from liquid to vapor, but you still have gasoline. It smells the same and it will still burn. That is a physical change. If you burn gasoline, there is again a change from liquid to vapor, but you no longer have gasoline. It smells different and it will no longer burn. That is a chemical change.

Later in the course you will have more criteria on which to base such a decision, but for now you will have to base such decisions on what you are able to observe.

So what kinds of changes can be observed? Well, they are the same as the properties themselves: phases, colors, clarity, homogeneity, temperatures. For example we can observe solids, liquids, and gases. Therefore, we can also observe the change from solid to liquid or liquid to gas or solid to gas. We can observe that something is blue or yellow or colorless, and we can also observe that something changes from colorless to pink or that something blue and something yellow, when mixed together, become green. We can observe that something is cool or hot. We can also observe that it changes from hot to cool.