Chemical Equations

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Chemical Equations
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Evidence of a Chemical Reaction
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1. Change in Odor
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2. Formation of precipitate

• Formation of a solid from a solution
• Such as Soap Scum

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3. Release or absorption of heat/energy
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4. Change in Color
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5. Escaping of Gas

• Bubbling
• Smoking
• Fizzing

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Chemical Equationsthings it tells us

• 1) The reaction that occurs between two or more
  substances
• (called reactants)

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• What is produced from the reaction
• (called products)

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2 H2 (g) O2 (g) 2 H2O (aq)

• The above example shows a chemical equation where
  hydrogen and oxygen react to produce water.

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• The arrow shows direction
• of the reaction

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The reactants are on the left side of the arrow!
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The products are on the right side of the arrow!
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The state of matter is represented in parentheses
around each substance

• (s) solid
• (g) gas

• (aq) aqueous
• (dissolved in water)
• (L) liquid

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The Law of Conservation of Matter states that
matter is neither created nor destroyed only
rearranged !
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Always True

• If you take an atom inventory, the number of
  atoms on the left side of the arrow should ALWAYS
  EQUAL the number of atoms on the right side of
  the arrow
• Atoms are never lost or gained, they are only
  rearranged!

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Rules for Balancing

• 1st Take an atom inventory
• of both sides !

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• 2nd Add a coefficient in front of the compound
  in order to balance the atoms of each element in
  the equation. You cannot change subscripts
  !!!!
• Note coefficients must be in the lowest,
  reduced form !

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Examples

• 6 Mg 2 N2 2 Mg3N2
• Are these coefficients in reduced form?
• NO
• Put them in reduced form.
• _ Mg _ N2 _ Mg3N2

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3rd Check to see if an element appears more
than once on the same side of the arrow

• Example
• CH4 O2 CO2 H2O
• oxygen appears twice on the
• product side

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• If an element appears more than once on the same
  side of the arrow, then balance that element
  LAST!!!!!!