Energy Changes

This is the fourth and final topic for year 9. Use this tackk to learn the basic definitions of the key words you need to know.

The Big Idea: When chemicals change to other forms there is an energy change.

Task 1: Write down as many energy changes as you have heard of before.

Task 2: Clap your hands and keep them closed. You have just made a bond. Did this give out energy?

Pull your hands apart. You have just broken a bond. Did this motion require energy?

From that little activity, you should learn that making bonds releases energy and breaking bonds requires energy.

Task 3: Name the following phase changes:

Gas to a liquid:

Liquid to a solid:

Solid to a liquid:

Liquid to a gas:

Now watch this video and find out whether these phase changes are exothermic or endothermic.

So how can we tell if a chemical reaction is endothermic or exothermic? Have a look at the diagram below.

#Feeling Challenged: Let's have a look at some energy profile diagrams. By looking at the energy of the reactants and the products, complete the following sentences using the following words:

released to            endothermic        more           less        absorbed from          exothermic

The first graph shows that the reactants have ___________ energy than the products. Therefore, energy is _______________the surroundings during the reaction. This reaction is ______________.

The second graph shows that the reactants have ____________ energy than the products. Therefore, energy is ________________the surroundings during the reaction. This reaction is _______________.