DK - WOW! The Visual Encyclopedia of Everything

Concentrated dye

contains more dye

particles to collide

with the cloth

As crystals of potassium

permanganate begin to

dissolve, purple trails

spread through the

water, until an even

purple solution is formed

At temperatures above

140°C (284°F ) nitrogen

dioxide exists as a

brown gas

When a bread dough

mixture is left in a

warm place, carbon

dioxide bubbles appear,

making the bread rise

(^6) APPLYING HEAT
When a mixture of yellow
powder sulfur and silver-
grey iron filings is heated
to a high temperature, a
chemical reaction takes
place and iron sulfide is
formed. Without heat, the
substances would not react
with each other. Heat speeds
up most reactions, and cold
slows reactions down.
(^7) EXOTHERMIC
Thermite is a mixture of
aluminium and iron oxide.
When it is ignited at a high
temperature there is an
explosion, as the chemical
reaction produces a sudden
release of energy in the
form of light, heat, and
noise. Reactions that
produce heat are known
as exothermic reactions.
(^8) OXIDATION
Some chemical reactions
happen around us naturally.
One of the commonest
reactions is oxidation – when
substances gain oxygen.
Oxidation is happening when
metals rust, when wood
burns, and when we breathe.
In all these reactions,
substances are reacting
with oxygen from the air.
(^9) SOLUTIONS
A solution is a mixture in
which the molecules are
mixed so evenly and
completely that it seems like a
single substance. However, in
a solution, a chemical reaction
has not taken place. Neither
the solute (the substance
being dissolved) nor the
solvent (the substance that it
is dissolved in) have changed.
(^10) CATALYST
A catalyst is a molecule that
helps bring about and speed
up a chemical reaction, but
does not change itself during
the reaction. Natural catalysts
are called enzymes. Bread
dough rises because enzymes
in yeast cause a reaction that
produces bubbles of carbon
dioxide when it is mixed with
water and sugars.
At lower temperatures
the nitrogen dioxide
molecules pair up to
make clear dinitrogen
tetraoxide
4
5
9
10
97
If heated again,
brown nitrogen
dioxide reforms
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