Chemistry in room 11
> Chapter 6 > Information
are all kinds of energy but where do we get our energy from? Our most important
sources are: oil coal and natural gas. But when we use these fossil fuels we
pollute the environment. We also use nuclear energy but there are many risks and
dangers involved with this kind of energy e.g. nuclear waste.
Nowadays we have alternatives although they are still not fully used. Just think
of solar or wind energy.
are different types of energy:
-chemical energy: this is contained in fossil fuels like coal and oil.
-movement energy: this is found in the wind and the tides.
-electrical energy: in nature we can see this in lightning.
chemical rections energy will be used.
There are reactions where energy is released and there are reactions that need a
lot of energy.
Most reactions that release energy need some energy to get started.
The amount of energy is indicated in joules(J). On food you will often find the
term Kj which meand kilojoule. 1Kj=1000 joules.
We speak of a loss of energy when energy is not spent usefully. All energy which
is spent usefully is called efficient energy. So if the efficiency of a car is
35% only a small part of the energy is useful and the rest is probably just
Efficiency = efficient energy x 100 / total energy
a reaction the mass of substances does not change. When you melt 1 kilo of ice
you will get 1 kilo of water. This is always the case although it may seem that
it is not. This is due to the fact that we usually do not weigh the gasses that
are formed in a reaction. In 1790 a frenchman called Lavoisier found that in all
reactions mass stays the same.
Still mass is very important during a lab test. Substances always react in
certain mass ratio.
if after a reaction a certain substance is still present, this substance could
not react because the other substance had alresdy been used. So in industry it
is very important to know the exact mass ratio because in this way waste
materials can be reduced.
all rections have the same speed e.g. the rusting of iron does not go very fast.
The reaction-time is pretty long and reaction-speed is very low. It is also a
question of spread.
a substance is divided into small pieces or even powder it will react quicker
than if it is one big lump.
there is the concentration of a material. This defines the amount of a material
present in a mixture
is also possible to speed up the reaction time by putting in a catalyst. This is
a substance that helps and even is a part of a reaction, but is still there (unchanged)
after the reaction.
catalyst is not changed in the reaction. We also have catalysts in our body.
They are called enzymes and among other things they play a part in our digestion.
reaction speed depends on:
kind of material
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