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
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.
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.
·
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
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.
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
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
some fun balancing equations go to:
http://www.mpcfaculty.net/mark_bishop/balancing_equations_tutorial.htm
http://www.mpcfaculty.net/mark_bishop/balancing_equations_tutorial.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/Conservation_of_mass
Ø http://chemistry.about.com/od/chemistryquickreview/a/balanceequation.ht
Ø http://chemistry.about.com/od/chemistryquickreview/a/balanceequation.ht
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=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
