Homework: Chemical Reactions

1) List four examples of a physical change

1 Materials are broken or crushed

2 Change of state

3 Mixture created

4 Something is dissolved

2) State the fundamental difference between a physical and chemical change:

That a new substance is formed in a chemical changed.

3) List four signs of a chemical change:

1 Energy is produced or absorbed

2 A gas is given off

3 A precipitate forms

4 Permanent colour change

4) List the signs of a chemical change you see when you light a match

When you strike a match, you are setting off several chemical reactions that you can detect with your senses. As the match is burning you can see energy being emitted as light, feel the heat energy being emitted and smell new gases being produced. Once the match has burnt, you are left with a black piece of charcoal

5) Specify what happens in a:

a) exothermic reaction- a reaction that is released as a form of light. Match being struck

b) endothermic reaction- Is the reaction when a liquid turns into a solid state. Water to ice

c) spontaneous reaction- An instant reaction. A modern ice pack where you press the button and it reacts and goes cold.

d) non-spontaneous reaction- Needs input from an external force.

Fuel in a car, needs to be burnt to work.

7) Describe a solution:

A mixture of two or or more substances

8) A solution is clear but not always colourless means that it could be cloudy or misty.

9) what happens when a precipitate forms?

A precipitate is the result of a reaction.

10) burning methane is a spontaneous reaction because it happens as soon as you put the flame in front of the gas.