Chemical Equations

Law of Conservation of

Matter: Matter cannot be created

or destroyed.

AMOUNT OF REACTANTS = AMOUNT OF PRODUCTS ! ! ! !

Guidelines for Balancing Chemical

Equations:  1) Do NOT change the subscripts !

2) Every element MUST have the same amount of atoms on both sides of the equation.

3) Add stoichiometric coefficients (numbers) in front of the chemical formula.

4) Once a coefficient is added, go back and

check the rest of the equation.

5) Leave hydrogens and oxygens to last. Balance hydrogens with an even number.

6) CHECK EQUATION TO BE SURE EVERYTHING BALANCES/CANCELS OUT ON BOTH SIDES ! ! !

Guidelines (cont.)

Diatomic elements

Bromine (Br2)

Chlorine (Cl2)

Fluorine (F2)

Hydrogen (H2)

Iodine (I2)

Nitrogen (N2)

Oxygen (O2)

Balances metals and then nonmetals.

Elements found in only ONE compound on each side—balance first

Polyatomic ions usually stay together—balance as a unit.

Elements in diatomic state? Balance compounds with these elements using an EVEN number

Do not be afraid to use FRACTIONS as coefficients !! Use common multiplier and multiply all coefficients to get rid of

the fraction

Helpful Hints

Example 1:

KI (aq) + Pb(NO3)2 è KNO3 + PbI2

Example 2:

C2H6 + O2 CO2 + H2O

Practice

1)   FeI3 + K2SO4 è KI + Fe2(SO4)3

2) CaSO4 + Al(NO3)3 è Ca(NO3)2 + Al2(SO4)3

Telling a story….

Writing Chemical Equations

1) Identify reactants, write chemical formulas.

2) Identify products, write chemical formulas. 3) Write the complete chemical equation.

4) Balance the equation.

Example 1:

Merry and Pippin find lead (II) chloride and lithium sulfate in Gandalf’s chemical supply cabinet. They combine these chemical compounds and then run to Gandalf so he may identify the produced chemical compounds. Gandalf identifies the compounds as lead (II) sulfate and lithium chloride.

Example 2:

A chemist at a Wake Forest chemistry lab prepares a potassium bromide solution dissolved in water to react with chlorine gas. This reaction produces bromine in the liquid state and potassium chloride in solution.

Merry and Pippin have gotten in over their

heads AGAIN!! Without Gandalf, they have combined a liquid phosphorus-chlorine compound which is 77.45% Cl by mass with water. Gandalf hears the commotion and immediately returns to identify an aqueous solution of phosphoric acid and hydrochloric acid.

Example 3: