Balancing Chemical Equation

Cecile N. Pelon

 BSED-Biological Science Major

Partido State University

College of Education

Goa, Camarines Sur

czelle_09cute@yahoo.com

czellepelon@gmail.com

"To every action there is always opposed an equal reaction."

 -Isaac Newton. (n.d.).

 Retrieved February 13, 2013, from BrainyQuote.com 

v    Balancing a chemical equation is much like the work of an accountant who has to show every penny that comes in and where it has gone to.

v   Law of Conservation of Mass

You need to remember this law!

v  The Law of Conservation of Mass states: that mass is neither created nor destroyed in any chemical reaction. Therefore balancing of equations requires the same number of atoms on both sides of a chemical reaction.

Because of the principle of the Conservation of Matter, an equation must be balanced. It must have the same number of atoms of the same kind on both sides.

v        The number of atoms in the Reactants must equal the Number of atoms in the Products

http://www.bbc.co.uk/schools/gcsebitesize/science/images/4_equations.gif

           Figure 1:Two atoms of copper react with two atoms of oxygen to form two molecules of copper oxide.

v    Law of Conservation of Mass

v   The mass of all the reactants (the substances going into a reaction) must equal the mass of the products (the substances produced by the reaction).

v   Reactant + Reactant = Product

Example

http://www.middleschoolchemistry.com/img/content/multimedia/chapter_6/lesson_1/balanced_equation.jpg

Figure 2: Methane react with oxygen  produce two water and carbon dioxide.
methane+ oxygen à carbon dioxide + water

CH4 + 2O2   à CO2 + 2H2O

·         Note that in a chemical equation, by convention, we use the arrow “  à  ” instead of the equals “ = ".

·         The last stage is to put in state of matter symbols, (s, l, g, aq), as appropriate (solid, liquid, gas, aqueous or dissolved in water)

CH4 (g) + 2O2 (g)   à CO2(g) + 2H2O(l)

·         Reactant- are written on the left side

·         Products-  are written on the right side

·         Coefficient- a number written before the symbol

·         Subscript- a number written below the symbol or formula

·         Chemical state- a substance merely refers to whether its a gas, liquid or solid 

v  Steps to Balancing a Chemical Equation
1.  Translating the statements.Write all reactants on the left and all products on the right side of the equation arrow. Make sure you write the correct formula for each element
2.  Balancing the atom.Use coefficients in front of each formula to balance the number of atoms on each side.
3.   Adjusting the coefficients.Multiply the coefficient of each element by the subscript of the element to count the atoms. Then list the number of atoms of each element on each side.
4.   Checking.It is often easiest to start balancing with an element that appears only once on each side of the arrow. These elements must have the same coefficient. Next balance elements that appear only once on each side but have different numbers of atoms. Finally balance elements that are in two formulas in the same side.

v   Re-cap of steps from rule 4:

·         Balance elements that appear only once on each side of the arrow.

·         Next balance elements that appear only once on each side but have different numbers of atoms.

·         Finally balance elements that are in two formulas in the same side.

5. Specifying the states of matter. Indicate the states of the reactants and products.

      

·         Use (g) for gaseous substances.

·         Use (s) for solids.

·         Use (l) for liquids.

·         Use (aq) for species in solution in water.

Write the state of matter immediately following the formula of the substance it describes.

Example

NH₃ + O₂     à    NO + H₂O

                                                       Reactants                Products
v  N appears once on both sides in equal numbers, so the coefficient for NH3 is the same as for NO.

NH₃ + O₂   à    NO + H₂O

v  Next look at H which appears only once on each side but has different numbers of atoms, 3 on the left and 2 on the right. The least common multiple of 3 and 2 is 6, so rewrite the equation to get 6 atoms of H on both sides:
                                2NH₃ + O₂   à NO + 3H₂O

     

2NH3 + O2   à NO + 3H2O

v  There are 2 oxygen atoms on the left and 5 on the right — the least common multiple of 2 and 5 is 10, so rewrite the equation as:

2NH3 + 5O2     à  4NO + 6H2O

Now count the atoms on each side:

2NH₃ + 5O₂   à 4NO + 6H₂O

 Write them out keeping them on the appropriate side of the chemical equation

2 N (nitrogen atoms)     4 N (nitrogen atoms)

6 H (hydrogen atoms)      12 H (hydrogen atoms)

10 O (oxygen atoms)    10 O (oxygen atoms)

v  This shows the equation not to be balanced “YET”

Check the number again:

v  If you double the N and H on the left the equation will be balanced:

4NH3 + 5O2   à 4NO + 6H2O

Double-check:

4NH₃ + 5O₂  à  4NO + 6H₂O

4 (nitrogen atoms) 4

12 (hydrogen atoms)12

10 (oxygen atoms) 10

The equation is Balanced.!

v  Balancing Practice

             For more help go to: 
http://richardbowles.tripod.com/chemistry/balance.htm#part0

              For some fun balancing equations go to:
http://www.mpcfaculty.net/mark_bishop/balancing_equations_tutorial.htm

           http://www.sciencegeek.net/APchemistry/APtaters/EquationBalancing.htm

v  Reference

•            Raymund Chang, General Chemistry , First edition, Pages 70-72.
•            Silberberg, Chemistry-The Molecular Nature of Matter and Change, Second Edition, Pages 103-106.

Ø  http://en.wikipedia.org/wiki/Chemical_equation

Ø  http://en.wikipedia.org/wiki/Conservation_of_mass
Ø  http://chemistry.about.com/od/chemistryquickreview/a/balanceequation.ht

Ø  http://wiki.answers.com/Q/What_symbols_are_used_for_chemical_equations

Ø  http://www.brainyquote.com/quotes/keywords/reaction.html#BgPwbcSl6mBbuqy6.99 
Ø  http://www.google.com.ph/search?q=image+of+the+atoms+that+was+balanced&hl=en&tbo=u&tbm=isch&source=univ&sa=X&ei=RxAbUaLCAcXRigLMmIDoDw&ved=0CCkQsAQ&biw=1024&bih=634#imgrc=BN0U4JDsdiX39M%3A%3B-RWudPHe0YR2OM%3Bhttp%253A%252F%252Fwww.middleschoolchemistry.com%252Fimg%252Fcontent%252Fmultimedia%252Fchapter_6%252Flesson_1%252Fbalanced_equation.jpg%3Bhttp%253A%252F%252Fwww.middleschoolchemistry.com%252Fmultimedia%252Fchapter6%252Flesson1%3B745%3B200

Ø  http://www.google.com.ph/search?q=image+of+the+atoms+that+was+balanced&hl=en&tbo=u&tbm=isch&source=univ&sa=X&ei=RxAbUaLCAcXRigLMmIDoDw&ved=0CCkQsAQ&biw=1024&bih=634#imgrc=GFUp-Hppsg34yM%3A%3BSlb_d9pKRCwqRM%3Bhttp%253A%252F%252Fwww.bbc.co.uk%252Fschools%252Fgcsebitesize%252Fscience%252Fimages%252F4_equations.gif%3Bhttp%253A%252F%252Fwww.bbc.co.uk%252Fschools%252Fgcsebitesize%252Fscience%252Fadd_gateway_pre_2011%252Fperiodictable%252Ffundamentalrev3.shtml%3B546%3B207