Balancing Equations
Objective-balance equations by adding appropriate coefficients
Review: Counting Atoms
Subscripts
How many atoms of hydrogen are in sulfuric acid?
Formula H2SO4 # H atoms 2
A subscript tells you the number of atoms for the
element immediately before
Parentheses
How many atoms of oxygen are in calcium phosphate?
Formula Ca3(PO4)2 # O atoms 8
Putting (…) around a polyatomic ion and then a
subscript tells us to distribute the subscript
outside to all elements inside ()
Example #1
Write the balanced chemical equation for the electrolysis of water
 You may only ADD or CHANGE coefficients!! You must remember that the
subscripts in formulas come from criss-cross or the prefix system
2H2 + O  2H2O
Example #2
Write the balanced chemical equation for hydrochloric acid added to magnesium metal
 Balance hydrogen and oxygen last—since they are in so many compounds—hopefully
they will balance with the coefficients you’ve already put in
Mg + 2HCl  MgCl2 + H2
Example #3
Write the balanced chemical equation for the decomposition of potassium chlorate
 TRICK--If you end up with an odd number of oxygen on one side and an even number
of oxygen on the other—double the coefficients you already put in
2KClO3  2KCl + 3O2
T. O’Toole
Minute Paper
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How do I get from where I am to where I’m going?
The 10 Minute Makeover
Customize your learning by choosing from the following options each night
 Complete the appropriate section on the Portfolio Page
 Check out the video with questions inserted in it on the website
 Complete SYS Assignment related book work
 Complete the required SYS assignment: “Reactions 6”
 Complete the required SYS assignment “Practice Test”
 Review the PPT file on the website
 Read pages 207-211 in the book
 Practice using: http://www.quia.com/jg/1309070.html
 Check out the tutorial resources in the LiveBinder
 Review the skills from today’s Train Your Brain
T. O’Toole