4.2 From reactions to balancing equations

• Scheikunde
• Middelbare school
• havo, vwo
• Leerjaar 3

Chemical reactions and equations

How can you tell that a chemical reaction has taken place?

Types of reactions

You can divide the reactions up in three broad types:

1. decompositions:
   one reactant -> multiple reactions products 
2. combustions:
    reactant + oxygen -> reactions product(s)
3. other reactions:
   multiple reactants -> reactions product(s)
   

What is a decomposition?

1. A reaction with oxygen
2. A reaction with one reactant and multiple reaction products
3. A combustion
4. A reaction with multiple reactants and one reaction product

Types of decomposition

1. elektrolysis, analysis, hydrolysis
2. thermolysis, electrolysis, photolysis
3. photolysis, thermolysis, kinelysis
4. thermolysis, luminysis, electrolysis

chemical reaction or chemical equation?

You can make a chemical equation out of a chemical reaction.

A chemical reaction is in words. 

A chemical equation is in symbols and needs to be balanced. 

chemical reaction

Start: methane and oxygen

End: carbondioxide and water

Give the chemical reaction for the decomposition of the substance aluminiumoxide (l)

+

+

Chemical reaction of photosynthesis

glucose

water

carbondioxide

oxygen

You can tell what happens with a chemical reaction, but not how many of each substance is needed or used

Chemical reaction to chemical equation

A chemical equation:

• uses formulas to indicate which substances react with one another and which new substances form
• uses the ratio in which the molecules react with one another and which new substances form
  

Rules for balancing equations

• after the reaction each type of atom needs to have the same amount as it had before the reaction
• You can't alter the molecules which you have themselves (so you can't alter the index
• There are no half molecules, if you get to a half number you will have to multiply all of the coefficients by 2 
• The coefficients need to be the lowest possible whole number 

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