Contents:-
Decomposition
Neutralization
Oxidation
Reduction
Redox
Polymerization
Photosynthesis
Respiration
Exothermic
and Endothermic
Displacement
Precipitation
Decomposition:-when
a compound breaks down into simpler compounds or elements. This happens
when the bonds between the atom weakens by heat or by adding a catalyst
(a chemical which can alter the speed of a chemical reaction without getting
involved).
e.g.
calcium carbonate------(heat)---- calcium oxide + carbon dioxide
When
you eat, the enzyme (biological catalyst) called amylase in your saliva
decomposes starch into glucose.
starch
----amylase---- glucose
Neutralization:-
when an acid cancels the alkalinity a base or vice versa. When an acid
reacts with a base, the result is a neutral substance or substances.
metal
oxide (base) + acid = salt + water
Because
bases and acids always have metals and non-metals, salts are always produced
as a result of neutralization.
metal
hydroxide + acid = salt + water
Because
all bases and acids have oxygen and hydrogen then the result of neutralization
is always water.
metal
carbonate + acid = salt + water + carbon dioxide
Because
all carbonates have carbon and oxygen, the result is carbon dioxide.
e.g.
sodium hydroxide + hydrochloric acid ------ sodium chloride + water
NaOH
+ HCl = NaCL + H20
If you
use hydrochloric acid, the salt will always be a chloride, if you use sulphuric
acid, the salt will be a sulphate and a salt will be a nitrate if nitric
acid is used.
Oxidation:-
when any substance reacts with oxygen or releases hydrogen, the result
is an oxide. Oxidation may need time to occur (e.g. rusting) or it may
need heat (e.g. burning). When metals like iron corrode or rust, the result
is iron oxide.
iron
+ oxygen ----water---- iron oxide
When
other metals or substances burn, the result is an oxide.
magnesium
+ oxygen ----heat---- magnesium oxide
Reduction:-
when a substance reacts with hydrogen or releases oxygen. One example of
reduction is when iron is produced from iron oxide in a blast furnace.
iron
oxide ------ iron + oxygen
We can
also call this decomposition.
Redox:-
when REDuction and OXidation occur at the same time (REDOX). When hydrogen
is passed over hot copper(II) oxide, this reaction takes place:
copper(II)
oxide + hydrogen ----- copper + water
CuO
+ H2 ------ Cu
+ H2O
In this
reaction copper has been reduced while hydrogen has oxidized.
Polymerization:-
When monomer molecules bond together to form a polymer. There can be 50,000
monomers in one polymer. One example is making polythene from ethene.
Photosynthesis:-
when energy from the Sun is stored in a sugar called glucose. Glucose is
formed when carbon dioxide reacts with water.
6CO2
+ 6H20 -----sunlight and chlorophyll----
602 + H12C6012
In this
reaction, water was split into hydrogen and oxygen. Oxygen was released
into the air while the hydrogen reacted with carbon dioxide.
Respiration:-
Respiration is the opposite of photosynthesis. Its target is to release
energy from glucose. It is very similar to burning or oxidizing.
602
+ H12C6012-----sunlight
and chlorophyll----6CO2 + 6H20
Exothermic
and endothermic:- any reaction which takes in more heat than it produces
is an endothermic reaction. Any reaction which produces more heat than
taking is an exothermic reaction. Oxidation and respiration are exothermic:
they release energy. In an exothermic reaction, energy used up to bond
the elements together in the outer-most is released as heat while the reverse
happens in endothermic reactions. The mass of a substance increases by
1 trillionth of a gram in endothermic reactions and decreases by 1 trillionth
of a gram in an exothermic reaction but you don't notice it.
Displacement:-
One substance pushes out another to take its place. For example, if an
iron nail is placed in copper(II) sulphate solution, some iron dissolves
and displaces copper in the solution, because iron is more reactive than
copper. A substance becomes more reactive when its outermost shell needs
to take or release a few electrons to become full or empty. In other words,
an element becomes more reactive as is its group number decreases. The
copper is deposited on the nail as brown coating:
iron
+ copper sulphate -------- copper + iron sulphate
In this
reaction, the oxygen in the acid reacted with the metal and the hydrogen
was released.
metal
+ acid ----- metal oxide + hydrogen
Precipitation:-
When some solutions are mixed, they react and give a product which is insoluble.
It appears as tiny, solid bits called a precipitate.
e.g.
silver nitrate (soluble) + sodium chloride (soluble) =
silver
chloride (insoluble precipitate) + sodium nitrate (insoluble)