Chemistry Definitions

Why Study Chemistry?

Chemistry is the central science that can explain the rapidly changing world in which we live. The most insignificant changes involve chemistry. Even some of those personal experiences we all treasure involve chemistry. As we read these pages, chemical reactions are occurring that allow us to see, to process the nerve signal to our brain and then analyze the images that we think of as words.

The rapid growth of technology has made some understanding of chemistry essential for not just scientists, but everyone. The choices we make in our lives not only impact our own personal well being but the well being of others around us.

We live in a global community and the changes that we, as a society, make will have a lasting legacy. Some changes are beneficial and some, appearing beneficial at the moment, have long-term negative effects on our environment and subsequently our health.

Learning Objectives

What is Chemistry?

Chemistry is the study of the composition of matter and the changes that matter undergoes. What then is matter?

The changes of matter can be either physical or chemical changes.

What is a physical change?

Physical changes involve changing the physical state of an element or compound. What are the physical states of matter?

What do you have to do to change the physical state of matter?

Physical properties refer to the nature of matter such as physical state, mass of a given volume, color, heat conductivity, electrical conductivity, melting point and boiling point.

What is a chemical change?

Chemical changes occur when an element or molecule reacts with another element or molecule to form completely different compounds.

Chemical properties refer to the behavior of matter with respect to how it changes composition when it interacts with other matter, light, or heat. Can you think of a chemical change?

What is a pure substance?

A pure substance is homogeneous and does not contain any different substance. A pure sample of water will always have the same physical and chemical properties regardless of where it is found and will not have any other chemical element or compound present.

If you boil water and collect the steam and let it cool back to the liquid state, will this water be pure?

What is the scientific method?

Chemistry is an experimental science that uses the scientific method. The scientific method is a process by which theories are formed.

· A phenomenon is observed and a hypothesis is proposed as to the solution to that phenomenon.

· A hypothesis is a speculation and has not been proven.

· Experiments are performed to test the hypothesis and if these experiments are successful and repeatable, the hypothesis becomes a theory.

Scientists publish their research results in refereed journals. This gives some check on the validity of their research. When someone states something in a non-refereed publication…it may or may not be valid. Always be a bit skeptical in what you read or hear especially when someone wants you to buy something.

Problems...Click on the question for the answer.

1. Classify the following as either a chemical or physical change.

Burning wood

Crushing a rock

Dissolving sugar in water

The rusting of iron

2. Classify the following as to whether or not they are pure substances or mixtures.

milk

table salt

sugar

steel

3. A cup of black coffee is considered to be __?__ and a/an __?__ substance.

(a) homogeneous…..pure

(b) homogeneous…..impure

(c) non-homogeneous…pure

(d) non-homogeneous…impure

4. The boiling of water is considered to be a __?__ change and the temperature at which water boils is considered to be a __?__ property.

(a) chemical…..chemical

(b) chemical…..physical

(c) physical…..chemical

(d) physical…..physical

Return to the Reviews of Concepts