Physical and Chemical Change
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What a physical change?
- Physical change occure when a substance changes, but no new substance is formed.
- Physical changes happen when a substance..
- Changes shape
- Crushed or broken
- Changes state
What is a chemical change?
- A chemical change or chemical reaction has occurred whenever a new substance has formed.
- In a chemical reaction the substances you start with are called the reactants.
- The substances youb end up with are called it's products.
- You can write a chemical reaction as a chemical equation.
- The four basic types of chemical reactions are..
- Combination reactions
- Breaking-down reactions
- Precipitation reactions
- Combustion reactions
- In combination reactions, reactants combine to form a single new substance.
- Eg. Iron + Oxygen gas --> Iron oxide
- Combination reactions are sometimes also called synthesis reactions.
- In breaking down reactions one substance breaks up into a number of smaller ones.
- Eg. Silver chloride --> Silver + chlorine
- Breaking-down reactions are also known as decomposition reactions.
- When a solid forms after two solutions are mixed it is called a precipitate.
- Eg. Silver nitrate solution + Sodium chloride solution --> Silver chloride precipitate + Sodium nitrate solution
- Precipates are insoluble (unable to disolve in water).
- Combustion reactions happen whenever you burn or explode something. A substance reacts with oxygen, usually from the air around it. New (often
- gaseous) substance form and heat and light may be released, sometimes a flame or explosive flash.
- Eg. Methane gas + Oxygen gas --> Carbon dioxide gas + Water vapour
Speeding up reactions
- The rate of reaction can be affected by:
- Amount or concentration
- Surface area
- Helper chemicals
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