Transcona Community Learning CentreCHEM 30S
LESSON 1: STATES OF MATTER
When you have completed this lesson, you will be able to:
- Describe the properties of gases, liquids, solids, and plasma in terms of density compressibility and diffusion.
Physical and Chemical Properties
Just like we identify people as our friends, family or strangers by their characteristics, we can distinguish between different kinds of matter by their characteristics or properties.
We identify people based on their looks and how they react under different circumstances. Matter is identified largely in the same way.
The physical properties of a substance are those that can be observed without changing the identity or make-up of that substance. For example, what is the substance's colour? Does it have a shiny or dull lustre? Is it soft or hard? Is it brittle or malleable? What is its density? Is it solid, liquid or gas at room temperature? How well does it conduct heat or an electric current? In order to test these properties, we do not need to change the identity of that substance.
The chemical properties of a substance describe how that substance reacts with other substances. These are properties that can be observed only when the substances identity is changed. For example, is the substance flammable (that is, does it burn?)? Does the substance rust or tarnish? Does it react with an acid? In all of these, testing for these properties will change the identity of the substance.
Physical Changes
When you tear up a piece of paper, saw some wood, or heat up an iron nail, the identity or nature of that substance does not change. These are all examples of a physical change in matter. A physical change involves a change in shape or a change in state of a substance.
When water is boiled (you can try this at home) and a burning splint or match is placed into the steam, the match will go out. If you put a burning match into water it also goes out. Water does not support burning either as a liquid or a gas. The chemical nature of the water does not change when the water goes from a liquid to a gas. When a substance changes state, it is a physical change since the identity or chemical make-up of that substance remains the same. Water is always H2O, two hydrogen atoms and one oxygen atom, whether it is liquid water, steam or ice. The chemical make-up does not change if we boil, freeze, or melt a substance.
Chemical Changes
If you burn the paper or the wood from the previous page, or allow the nail to rust, the identity of what remains has changed. The wood and paper have turned into a black brittle substance that cannot be written on or support you in a chair. The nail turns into a reddish-brown crumbly substance, completely unlike the original nail. In each of these cases, a chemical change has occurred.
A chemical change has occurred when new substances with new properties are formed.
We can tell if a chemical change has occurred if one or more of the following is observed:
- a change in colour,
- f izzing or bubbling,
- the container feels warmer, heat is released. We call this an exothermic change. (exo = out, therm = heat, so exothermic is heat given off)
- the container feels cooler, heat is absorbed. We call this an endothermic change. (endo = in, therm = heat, so exothermic is heat taken in) and/or
- when two clear liquids are mixed, a solid forms or the mixture goes cloudy. This is called precipitate formation.
The Four States of Matter
From previous science courses, and everyday life, you likely know that there are three common states of matter: solid, liquid and gas. But there are actually four states of matter: solids, liquids gases and plasma. We will discuss plasma a little later. First we will examine the three commonly known states or phases of matter..
Following are some characteristics of the three most commonly known states or phases of matter:
Solid / Liquid / Gas
Shape / definite shape / takes the shape of its container / takes the shape of its container
Volume / definite volume / definite volume / takes the volume of its container
Density / usually very dense / usually less dense than solid / usually much less dense than solid and liquid
Compressibility / not easily compressed / not easily compressed / easily compressed
Diffusion / not easily / easily / very easily
Diffusion refers to how easily substances are able to move through other substances. For example, when someone with very strong cologne walks into a room the smell, or odour, spreads through the whole room. Eventually everyone can smell the cologne. We say the smell diffuses through the room. The particles that carry the odour move through the air and distribute throughout the room quickly and easily. In order for particles of one type of matter to move easily through another type of matter, there must be very little interaction between the particles and there must be space for the particles to move.
Plasma
Plasma can be defined as a gaseous mixture of positive ions and electrons. The only way to have large number of these energetic particles co-existing together is at temperatures over 100 million degrees Celsius. The challenge for engineers is to contain high-energy plasmas once they are created.
Although not commonly known, plasma actually is the most abundant of all types of matter in the universe, but the least abundant on Earth. About 99% of all matter in the universe is plasma. Examples of plasmas include the aurora borealis, stars (produced from nuclear fusion) and lightning bolts. Here on Earth, scientists are able to use the principles of plasmas practically in fluorescent lights and plasma TV’s/monitors.
SUMMARY:
In this lesson we have learned
- A physical property is a characteristic that can be tested without changing the composition of the substance.
- A chemical property can only be tested by changing the identity of the substance.
- A physical change is a change in state or shape.
- A chemical change occurs when new substances with new properties are formed.
- The 4 states of matter are solid, liquid, gas and plasma.
Aug 2006Module 11