Revision sheets

Here are sample answers for the revision sheet from class today.  Make sure you have a look at it before the test on Friday!
1. For the water in a kettle, you need to draw the particles in a liquid (slightly spread out, moving slowly).  The steam occurs once the water has wamred up and particles have changed to gas.  These will be moving around very fast and more spread out than the liquid below them.
2. To make something go from a solid to a liquid or a gas it has to be heated (when energy goes in).  If something is cooling down from a gas to a liquid or liquid to solid (like the ice cream mixture), energy must be taken out of it.
3. Chemical changes

• are irreversible
• Can have colour changes
• Can produce new smells

4. Water boiling is a physical change not a chemical one as it can be reversed (cooling the steam will produce liquid water again).
5. The crepe directly touching the pan is heated by conduction.
6.

• Convection - Boiling a potato
• Radiation - Cooking with a microwave or a grill.

7. Raw eggs contain long string-like particles called proteins.  Normally they float around separately and keep a certain shape, but when they are heated they change shape and stick together.  This forms a solid and is an irreversible chemical change.
8. When ice cream forms by cooling a liquid and making a solid, water in the liquid becomes ice crystals.  The longer the mixture takes to freeze, the larger the ice crystals become.  This gives the ice cream a 'rough' feel in your mouth and makes it taste bad.  If it is frozen quickly, the crystals stay small and it tastes smooth.

Good luck, please come and find me if you have any questions!