Exothermic Reactions

Many chemical reactions give out energy in the form of heat, light or sound. Some reactions give out their energy over a long time.

An explosion, on the other hand, is an exothermic reaction in which all its energy is given out in a very short time

The energy comes from the bonds that hold the atoms together in the molecules. When these atoms join up during a chemical reaction they all give out a little bit of energy. Because there are millions and millions of molecules the energy they all give out adds up to make heat, a flame or even an explosion.

 

Now fill in these missing words ...

Molecules are made up of small particals called which are held together by . In a chemical reaction the bonds break apart and then join up again in a different way. When this happens a little is given out. This energy is very weak - but there are millions of each giving out energy. All this adds up so that a lot of energy is produced.

In an experiment we could measure the amount of heat energy given out by a chemical reaction. We could measure the change in temperature using a which we would put in the mixture.
In our experiment one test tube gets warm ... the other one explodes into flames!
Both of these reactions are giving out in the form of heat. This type of chemical reaction is called an reaction. The first exothermic reaction gave out its energy over a time - but the exploding reaction gave out its energy in a very time.

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Exothermic reactions are used by us all the time. When we strike a match an exothermic reaction provides heat and light. An exothermic reaction between petrol and air causes energy to be released making a car engine work.
The trick is to catch as much of the energy given out in an exothermic reaction and then put that energy to good use in a controlled way.

 

Now answer these questions:

Molecules are made out of what ?

Atoms are joined together with what ?

When bonds join or break they give out what ?

A reaction that gives out energy is called what ?

A candle gives out energy quickly or slowly ?

A bomb gives out energy quickly or slowly ?

What do you use to measure the change in temperature ?

What type of energy causes a change in temperature ?

What other sort of energy does a candle give out ?

We hear another form of energy made by an explosion ... what is it ?

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