Balancing Chemical Equation. A chemical equation shows the starting compound(s)—the reactants—on the left and the final compound(s)—the products—on the right, separated by an arrow. In a balanced chemical equation, the numbers of atoms of each element and the total charge are the same on both sides of the equation.Each substance is specified by its chemical formula, optionally preceded by a number called stoichiometric coefficient. The coefficient specifies how many entities (e.g. molecules) of that substance are involved in the reaction on a molecular basis. If not written explicitly, the coefficient is equal to 1. Multiple substances on any side of the equation are separated from each other by a plus sign. The standard notation for chemical equations only permits all reactants on one side, all products on the other, and all stoichiometric coefficients positive. A chemical equation is the symbolic representation of a chemical reaction in the form of symbols and chemical formulas. The reactant entities are given on the left-hand side and the product entities are on the right-hand side with a plus sign between the entities in both the reactants and the products, and an arrow that points towards the products to show the direction of the reaction. The chemical formulas may be symbolic, structural (pictorial diagrams), or intermixed. The coefficients next to the symbols and formulas of entities are the absolute values of the stoichiometric numbers. The first chemical equation was diagrammed by Jean Beguin in 1615. In the symbolic equation, chemical formulas are used instead of chemical names for reactants and products, while symbols are used to indicate the phase of each substance. It should be apparent that the chemical shorthand method is the quickest and clearest method for writing chemical equations. n a chemical change, new substances are formed. In order for this to occur, the chemical bonds of the substances break, and the atoms that compose them separate and rearrange themselves into new substances with new chemical bonds. When this process occurs, we call it a chemical reaction. A chemical reaction is the process in which one or more substances are changed into one or more new substances. Reactants and Products To describe a chemical reaction, we need to indicate what substances are present at the beginning and what substances are present at the end. The substances that are present at the beginning are called reactants and the substances present at the end are called products. Sometimes when reactants are put into a reaction vessel, a reaction will take place to produce products. Reactants are the starting materials, that is, whatever we have as our initial ingredients. The products are just that—what is produced—or the result of what happens to the reactants when we put them together in the reaction vessel. If we think about baking chocolate chip cookies, our reactants would be flour, butter, sugar, vanilla, baking soda, salt and chocola

2. How molecules are symbolized
Cl2 2Cl 2Cl2
• Molecules may also have brackets to
indicate numbers of atoms. E.g. Ca(OH)2
O
H
O
H
Ca
• Notice that the OH is a group
• The 2 refers to both H and O
• How many of each atom are in the following?
a) NaOH
b) Ca(OH)2
c) 3Ca(OH)2
Na = 1, O = 1, H = 1
Ca = 1, O = 2, H = 2
Ca = 3, O = 6, H = 6

3. Balancing equations: MgO
• The law of conservation of mass states that
matter can neither be created or destroyed
• Thus, atoms are neither created or destroyed,
only rearranged in a chemical reaction
• Thus, the number of a particular atom is the
same on both sides of a chemical equation
• Example: Magnesium + Oxygen (from lab)
• Mg + O2  MgO O
Mg O
+  Mg O
• However, this is not balanced
• Left: Mg = 1, O = 2
• Right: Mg = 1, O = 1

4. Balance equations by “inspection”
Hints: start with elements that occur in one
compound on each side. Treat polyatomic ions
that repeat as if they were a single entity.
5
2 3
3.5
2 7 4 6
2 2
2
2 6
3
C2H6 + O2  CO2 + H2O
a) P4 + O2  P4O10
b) Li + H2O  H2 + LiOH
c) Bi(NO3)3 + K2S  Bi2S3 + KNO3
d) C2H6 + O2  CO2 + H2O
From Mg + O2  MgO
2Mg + O2  2MgO is correct
Mg + ½O2  MgO is
incorrect
Mg2+ O2  2MgO is incorrect
4Mg + 2O2  4MgO is incorrect

5. a) Mg + 2HCl  MgCl2 + H2
b) 3Ca + N2  Ca3N2
c) NH4NO3  N2O + 2H2O
d) 2BiCl3 + 3H2S  Bi2S3 + 6HCl
e) 2C4H10 + 13O2  8CO2 + 10H2O
f) 6O2 + C6H12O6  6CO2 + 6H2O
g) 3NO2 + H2O  2HNO3 + NO
h) Cr2(SO4)3+ 6NaOH  2Cr(OH)3+ 3Na2SO4
i) Al4C3 + 12H2O  3CH4 + 4Al(OH)3
Balance these skeleton equations:

6. a) 2KNO3  2KNO2 + O2
b) 2Pb(NO3)2  2PbO + 4NO2 + O2
c) P4 + 6I2  4PI3
d) 3MgO + 2H3PO4  Mg3(PO4)2 + 3H2O
e) Br2 + 2KI  I2 + 2KBr
f) Ca(OH)2 + 2HNO3  Ca(NO3)2 + 2H2O
g) Bi2O3 + 3H2  2Bi + 3H2O
h) 3Fe + 2O2  Fe3O4
i) 2CaO + 5C  2CaC2 + CO2
Here are some more to balance:

7. Question 3 pg. 252
a) 2Li + 2H2O  H2 + 2LiOH
b) P4 + 5O2  P4O10
c) 2C2H6 + 7O2  4CO2 + 6H2O
d) CS2 + 3O2  CO2 + 2SO2
e) 2AsCl3 + 3H2S  As2S3 + 6HCl
f) 3AgNO3 + FeCl3  3AgCl + Fe(NO3)3
g) 2KClO3  2KCl + 3O2
h) 2SO2 + O2  2SO3
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