Chemical Reactions

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Chemical Reactions
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What is a chemical reaction?

• A chemical reaction is a chemical change where
  chemical substances (called reactants) react to
  give new chemical substances (called products).
• Example
• The combustion of hydrogen in oxygen is a
  chemical reaction which gives water.
• Hydrogen and Oxygen are the reactants.
• Water is the product.

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Chemical reaction and molecules

• The chemical reaction of hydrogen and oxygen is
  done between the molecules of these two gases.
• In this chemical reaction, the bonds of the
  hydrogen molecules H2 and oxygen molecules O2
  break down.
• The atoms H and O form new bonds to give water
  molecules H2O.

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The three molecules

• Hydrogen molecule H2
• is made up of 2 atoms
• Oxygen molecule O2
• is made up of 2 atoms
• Water molecule H2O

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Chemical equation

• A chemical equation is a way which represents the
  rearrangement of the atoms during a chemical
  reaction.
• In a chemical equation, we write the formulas of
  the reactants and the formulas of the products
  separated by an arrow.
• hydrogen oxygen water
• H2 O2 H2O

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Lavoisiers Law

• Antoine Lavoisier, a french chemist, stated the
  following law
•  the number of atoms in the reactants the
  number of atoms in the products. 
• This law makes it possible to balance chemical
  equations

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Balance a chemical equation

• H2 O2 H2O
• There are 2 atoms H and 2 atoms O in the
  reactants.
• There are 2 atoms H and 1 atom O in the product.
• To balance this equation, we take 2 water
  molecules containing 2 atoms O and 4 atoms H, and
  we take 2 hydrogen molecules and 1 oxygen
  molecule.
• H2 and H2 O2 H2O and H2O
• We should write it
• 2 H2 O2 2 H2O

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To read a chemical equation

• 2 H2 O2 2 H2O
• Read this equation as follow
• 2 hydrogen molecules react with 1 oxygen molecule
  to form 2 water molecules.
• Attention
• The number of atoms is the same in the
  reactants and the products.
• The number of molecules is not necessarily the
  same.

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Problems

• Methane CH4 reacts with oxygen O2 to form carbon
  dioxide CO2 and water H2O.
• a. Balance the equation of this reaction
• CH4 O2 CO2 H2O
• b. Determine the number of reactants and products
  molecules.

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Problems

• Balance and read the following equations
• Na O2 Na2O
• Fe Cl2 FeCl3
• N2 H2 NH3
• Al O2 Al2O3
• Note FeCl3 Iron III chloride
• NH3 Ammonia
• Al2O3 Aluminum oxide

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Answers

• CH4 2 O2 CO2 2 H2O
• 1 methane molecule react with 2 oxygen molecules
  to form 1 dioxide carbon molecule and 2 water
  molecules.

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answers

• 4Na O2 2 Na2O
• 4 sodium molecules react with 1 oxygen molecule
  to form 2 sodium oxide molecules.
• 2Fe 3Cl2 2FeCl3
• 2 iron molecules react with 3 chlorine
  molecules to form 2 iron III molecules.

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Answers

• N2 3H2 2NH3
• 1 nitrogen molecule react with 3 hydrogen
  molecules to form 2 ammonia molecules.
• 4Al 3O2 2Al2O3
• 4 aluminum molecules react with 3 oxygen
  molecules to form 2 aluminum oxide molecules.