Balancing Chemical Equations

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Chapter 17

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Balancing Chemical Equations

• Reactants Products
• 2H2(g) O2(g) ? 2H2O(l)
• coefficents
• yields/produces
• reacts with
• reactants Products (g) gas
• H4 H4 (l) liquid
• O2 O2 (s) solid
• (aq) aqueous solution

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2H2(g) O2(g) ? 2H2O(l)
4 atoms of H
2 atoms of O
4 atoms of H 2 atoms of O

• When balancing equations
• ONLY THE COEFFICIENTS CAN CHANGE..
• NEVER CHANGE THE SUBSCRIPT!!!

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17.2 Balancing equations

• The law conservation of mass is applied by
  balancing the number and type of atoms on either
  side of the equation.

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17.2 Balancing equations

• Counting atoms is necessary to balance an
  equation.

How many carbon atoms?
How many hydrogen atoms?
How many oxygen atoms?
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17.2 Steps for balancing

1. Count the number of each type of atom on both
   sides.

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Lets begin balancing equations

• Example 1
• __Al __HCl ? __AlCl3 __H2
• Example 2
• __C2H4 __O2 ? __CO2 __ H2O
• Example 3
• __C5H10 __O2 ?__CO2 __H2O

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• Example 4
• __Zn __AgNO3 ? __Ag __Zn(NO3)2
• Example 5
• __NH3 __O2 ? __NO __H2O
• Example 6
• __AlBr3 __K2SO4 ? __KBr __Al2(SO4)3

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Basic Types of Reactions

• I. Combustion Reactions
• Involve hydrocarbons(Carbon Hydrogen) and
  related compounds reacting with O2 to form CO2
  and H2O.
• Ex1.
• 2C3H6 9O2 ? 6CO2 6H2O
• Ex2.
• 2CH3OH 3O2 ? 2CO2 4H2O

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• Addition/Combination Reactions
• Involve two or more substances which
  react to form one product.
• A B ? C
• Ex1.
• C(s) O2(g) ? CO2(g)
• Ex 2.
• CaO(s) H2O(l) ? Ca(OH)2(s)

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• Decomposition Reactions
• Occurs when one substance undergoes a
  reaction to produce two or more substances.
• C ? A B
• Ex1.
• 2KClO3(s) ? 2KCl(s) 3O2(g)
• Ex2.
• 2Na3N(s) ? 6Na(s) N2(g)

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Single Replacement

• A BX AX B
• Example
• Fe CuCl2 ? FeCl2 Cu

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Double Replacement

• AB CD ? AD CB
• Example
• Pb(NO3)2 2KI ? PbI2 2KNO3

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Atomic Molecular Weights

• Chemical formulas and chemical equations have
  quantitative significance.
• H2O means 2 atoms of hydrogen and 1 atom of
  oxygen.
• C3H8 5O2 ? 3CO2 4 H2O
• means 5 moles of oxygen gas

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• Ex 1
• Find the molecular weight of sucrose(C12H22O11).
• Ex 2
• Find the formula weight of Ca(NO3)2.
• Ex 3
• Find the formula weight of Al(OH)3.

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The Mole

• The mole A collection of Avogadros number of
  objects
• 6.02 x 1023
• Amedo Avogadro (1776-1856) determined the Moles
• number by experimentation
• 1 mole of 12C-atoms 6.02 x 1023 12C-atoms
• 1 mole H2O molecules 6.02 x 1023 H2O molecules
• 1 mole NO3- ions 6.02 x 1023 NO3- ions