Physical and Chemical Change

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Author:
Anonymous
ID:
101211
Filename:
Physical and Chemical Change
Updated:
2011-09-12 06:21:33
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Physical Chemical Change
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Description:
Science Dimensions 2 2.2
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  1. 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
    • Dissolved
    • Mixed
    • Changes state
  2. 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
  3. Conbination reations
    • 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.
  4. Breaking-down 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.
  5. Precipitation 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).
  6. Combustion reactions
    • 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
  7. Speeding up reactions
    • The rate of reaction can be affected by:
    • Amount or concentration
    • Temperature
    • Surface area
    • Helper chemicals
    • Enzymes

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