(^1) REACTION
When vinegar (acetic acid)
and chalk (calcium carbonate)
are mixed, a chemical reaction
takes place. The acidic vinegar
breaks down the chalk to
release carbon and oxygen
as bubbles of carbon dioxide.
The starting materials in a
chemical reaction are called
reactants. The materials that
exist after are called products.
Chalk and vinegar fizz
vigorously as the acid
breaks down the chalk
Burning is a non-reversible
reaction – the wick cannot be
remade from the ash and smoke
When chemicals in an
apple’s cells that contain
substances called phenols
are exposed to the
air, they oxidize and
turn brown
Silver metal clings
to the copper coil
The explosion caused by
igniting thermite produces
a temperature of around
2,400°C (4,350°F)
The atoms within a molecule are held together with
links called chemical bonds. In a chemical reaction,
the bonds between a molecule’s atoms break, and
the atoms bond in a different way to form new
molecules. In some reactions, elements combine to
create a compound. In others, compounds break
down into elements or simpler compounds. All
the atoms from the original substance exist in the
changed substance, but in different places.
Chemical reactions
REACTIONS
(^2) DISPLACEMENT
In a displacement reaction,
the metal that forms part of
a compound is removed and
replaced by another metal.
When a coil of copper is
dipped into a clear solution
of silver nitrate, the copper
displaces the silver from the
solution to form a blue
solution of copper nitrate and
needles of solid metal silver.
(^3) BURNING
When the wick of a candle
burns, it is reacting with
oxygen in the air to produce
ash and smoke. The burning
also produces energy in
the form of heat and light.
In all reactions, energy is
used up when bonds
between atoms break,
and energy is released
as new bonds are made.
(^4) REACTION RATES
The rate of a chemical
reaction is affected by factors
such as temperature,
pressure, light, surface area,
and concentration. It is
possible to change the rate
of a reaction by varying one
of these factors. For example,
increasing the concentration
of dye in a solution will dye
the material more quickly.
(^5) REVERSIBLE
A few reactions are reversible.
The molecules created by the
reaction can be reformed into
the original materials. The
initial reaction is called the
forward reaction and the
reverse is the backward
reaction. Dinitrogen tetraoxide
breaks down into nitrogen
dioxide when heated, but
reverts when cooled.
The energy produced when
sulfur and iron react causes
the mixture to glow
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