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 _______________.