Chemical Equations

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Chemical Equations
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Chemical Reactions

• Process in which new substances are formed with
  new properties
• Ex Na(s) Cl2(g) ? NaCl
• Sodium metal is very reactive, chlorine gas is
  poisonous, yet together they make table salt,
  yum!

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Types of equations

• Skeleton equation summarizes the reaction in
  symbol form.
• Ex H2 O2 ? H2O
• Balanced Chemical equation
• Ex 2H2 O2 ? 2H2O
• Word equation Hydrogen reacts with oxygen to
  produce water

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Writing Chemical Equations

• The sign means reacts with
• The arrow ? means to produce

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• the nominative formula however tells you nothing
  about the composition (formulas) of the reactants
  and productsso it is better to use balanced
  chemical equations
• Remember HOBrFINCl (all these are found as
  diatomic molecules when alone!!!)
• Ex H2, Cl2, Br2

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Law of Conservation of Mass

• states that the mass of the reactants in chemical
  equations must equal the mass of the products.
• So, lets consider again
• H2 O2 ? H2O
• How many hydrogen and oxygen atoms in the
• a) reactants?
• b) products?

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Balancing Equations

• You need to add coefficients to balance the
  equationto make sure that there are the same
  number of atoms of each kind on both sides.

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• Sometimes, you must indicate the state of the
  reactants and products
• For solids add (s) after the element symbol eg.
  Fe (s)
• For liquids add (l), eg. H2O (l)
• For gases, add (g), eg. O2 (g)
• For a substance dissolved in water (aq)
• eg. NaCl (aq)

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Recap
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Examples

• H2 Cl2 2HCl
• Zn 2HCl ZnCl2 H2
• See more examples in your text on pages 172-173.
• Do questions pg 174 3,4
• pg 177 17,18