Chemical reactions and energy (1)

2. Chemical reactions and
Energy

3. Oxidation
Some metals have a chemical
property which makes them react
when they are exposed to air.
Atoms in iron react with the
oxygen in the air. When this
happens, the atoms are changed
into a new substance.This new
substance has a brown colour and
is called rust.This process is called
oxidation. Oxidation also occurs in
some foods. Apples and potatoes
oxidise when they are peeled or
cut.

4. Fermentation
 Fermentation is a chemical reaction where fungi
or bacteria change organic substances into other
substances. During the process of fermentation,
fungi produce alcohol and bacteria produce lactic
acid. Oxygen does not take part in this reaction.
Fermentation is used to make foods such as
cheese or bread and drinks such as wine.
 Fermentation also occurs naturally in sugars in
fruits or vegetables, which helps with
decomposition.
 Fermentation is also used to preserve food all over
the world.Vegetables, fruit, fish, and meat can all
be stored for longer if they are fermented first.

5. Combustion
 Combustion is a chemical reaction that produces
energy in the form of heat and light. Combustion or
burning can happen when oxygen from the atmosphere
reacts with a fuel. Some examples of fuels are wood ,
gas or oil. When they burn, the atoms in the substance
react and form new substances, such as ash and smoke.
 During wood combustion, fuel turns into heat, ash and
smoke.
 During petrol combustion, fuel is converted into kinetic
energy and exhaust gases.

6. Challenge 1
 1.During oxidation of iron __________is
formed.
 2.When apple flesh combines with
___________, it oxidises and
turns______________
 3.What is needed for fermentation? What gas
is released during fermentation?
 4.What energy is produced during
combustion?
 5. Which gases does petrol combustion
exhaust?

7. Energy
 Changes caused by different forms of energy.
We can understand energy as the ability of
something to cause change. WE can then
classify energy changes according to the forms
the energy takes, and then show the energy
changes in the form of an energy chain.
 There are two categories of energy: Potential
energy is energy that is stored, so that
through some process it can be used to make a
change happen. For example?
 Kinetic energy is that the energy that things
have through movement. For example?

8. Some energy producers
These photos show
some different ways in
which energy from
nature is harnessed to
make electricity. What
are they?