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Chemistry in room 11 > Chapter 6 > Information

There 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. 

There 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.

In all 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 engine heat.

Efficiency = efficient energy x 100 / total energy 

During 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.

So 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.

Not 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.

When a substance is divided into small pieces or even powder it will react quicker than if it is one big lump.

Then there is the concentration of a material. This defines the amount of a material present in a mixture 

It 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.

A 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.

So reaction speed depends on:

1 the kind of material
2 the temperature
3 the spread
4 the concentration
5 a catalyst

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