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1. Some Basic Conceptions
1.1 Matter
Everything on the earth is made of matter. Matter has weight and occupies space. Iron is a kind
of matter. It has weight and occupies space. Air is also a kind of matter. It has weight and occupies
space.
Matter exists in one of the three states: solid, liquid, or gaseous. Iron is a solid. It is not a liquid
or a gas. Water is a liquid. It is not a solid or a gas. Air is a gas. It is not a solid or a liquid.
Each state of matter has definite properties.
Solids are hard and have definite form. Solids also have volume. Liquids have not any definite
form. They take only the shape of their container. Like solids, liquids have definite volume. Gases
have neither definite shape nor definite volume. Molecules of gases move faster. Gases can be
easily compressed.
Matter can be changed from one state to another. This kind of change in the state of matter is
only a physical change. The physical change does not change the chemical composition of matter.
A chemical change is different from a physical change. In the chemical change a new substance is
formed at least.
1.2 What Is Matter?
What is matter? Everything on the earth is matter. Air is a kind of matter. Water and iron are
also different kinds of matter. The earth itself is matter. The world is made of matter. Matter is in
constant motion and in constant change.
Matter has many properties. Different kinds of matter have different properties. However, all
matter has weight and occupies space. Iron has weight and occupies space. It is heavy. Air also has
weight and occupies space, but it is very light. Most kinds of matter have the three states. Matter
changes from one state to another at different temperature and pressure. At ordinary pressure,
water changes into steam at the temperature of 100°C and changes into ice at the temperature of
0°C. Changes of matter in states are called physical changes. A change in the size or temperature
of matter does not change its chemical composition.
1.3 Chemical Changes
Different kinds of matter have different physical and chemical properties. The properties of a
substance are its characteristics. We know one substance from another by their physical and
chemical properties. In a physical change the composition of a substance is not changed. Ice can
be changed into water. This is a physical change because the composition of water is not changed.
In a chemical change the composition of a substance is changed. One or more new substances are
formed.
Iron rusts in moist air. When iron rusts, it unites with the oxygen from the air. A new substance
is formed. It is iron oxide. It has other different properties. Wood will burn if it is heated in air.
When wood burns, it reacts with the oxygen from the air. New substances are formed. They are