Elements, Compounds and
Reactions
Objectives
Names the various forms of matter
Describes the composition of matter
Distinguishes between chemical and physical changes
Shows you how to construct formulae and equations
Matter and energy
The universe is composed of matter and energy. Matter is anything that occupies
spaceand has mass– rocks, oceans, the air that we breathe and we, ourselves, are all
composed of matter. Energy has no shape or form – it is defined as the ability to do
work.
Mass and weight
Suppose you have a solid rubber ball, which contains a definite amount of matter. If
you compress it, its volume reduces but the quantity of matter it contains remains
the same. If you took the ball to the Moon, it would still contain the same amount of
matter but its weightwould be different. The weight of a body depends upon the
attractive force exerted upon it by gravity and the force of gravity on the Moon is
much less than on Earth. The mass of a body, however, depends on the amount of
matter it contains and does not vary with location.
Although mass and weight are often used interchangeably, this is sloppy because
they are not the same. Chemists are concerned with the measurement of masses, and
here we shall use the term ‘mass’ in its proper context.
Work
If we try to move a mass, it resists our efforts. Workis done when a force acts on a
mass and moves it and this requires energy. Energyshows itself in many different
forms:
●Heat energyis released when fuels burn.
●Electrical energydrives videos, freezers and computers.
2.1
Contents
2.1Matter and energy 152.2Physical and chemical
changes 192.3Chemical formulae 202.4Writing and balancing
equations 241.5Revision questions 282
UNIT