Week 6 science homework Chemical Reactions
1. List four examples of a physical change.
Examples of physical change are: Change of state liquid, gas or solid for example ice
being melted into water. Materials are crushed, broken into smaller pieces. A solid
being dissolved in a liquid for example salt crystals dissolved in water the
characteristics of the sodium chloride changes. A mixture created by mixing two
different substances.
2. State the fundamental difference between a physical and a chemical change.
The difference between physical change and chemical change is that there is a new
substance created in a chemical change. Physical change is the properties of the
substance have changed.
3. List four signs of chemical change.
Four signs of chemical change include: Coluor change, if gas is given off, if energy is
created or absorbed or if precipitate is formed.
4. List the signs of chemical change you would observe when you strike a match.
Smoke is given off, energy is created with the heat, coulor change the match stick
would be black instead of its original coulor,
5. Specify what happens in:
a an exothermic reaction: In an exothermic reaction energy is released.
b an endothermic reaction: An endothermic reaction is when energy is absorbed in the
form of in heat, sound or light.
c a spontaneous reaction: Is when a reaction proceeds itself. The reaction keeps going
once it has been started.
d a non-spontaneous reaction: A non-spontaneous reaction needs a continuous electric
current to react, stop the current the reaction will stop.
6. State an example of each of the reactions in question 5.
Endothermic: Melting ice
Exothermic: Freezing ice
8. Explain what is meant by a solution is clear, but not always colorless.
You might be able to see through a solution as if it were clear but it would have a
color e.g you can still see through mixed cordial but it might be a green solution.
9. Describe what happens when a precipitate forms.
A precipitate is formed when two solutions are mixed but one is insoluble, doesn’t
dissolve in water if it is solid it will usually sink to the bottom.
10. Burning methane (natural gas) is a spontaneous reaction but you need to light a
match to make it burn. Explain why.
Any spontaneous combustion needs three things to burn, fuel, and oxygen and heat
source. Methane the fuel oxygen is present and the match is the heat source.