Balancing Equations Everyone should: Be able to balance simple equations that use up to 3 valence electrons Most people will: Balance equations using compounds like OH- NO3 - SO4 2- Some people will: Be able to balance equations with unusual compounds not covered in class

IMPORTANT ATOMS CANNOT BE CREATED OR DESTROYED!

Remember: Hydrogen and Chlorine are diatomic Hydrogen + chlorine  hydrogen chloride H2 + Cl2  HCl Remember: Hydrogen and Chlorine are diatomic  + REACTANTS 2 H atoms 2 Cl atoms PRODUCTS 1 H atom 1 Cl atom This is impossible as it implies that atoms have been destroyed.

What do we do? We need to make the number of atoms equal on both sides of the equation, in order to get the equation to BALANCE.

What do we do? We need to make the number of atoms equal on both sides of the equation, in order to get the equation to BALANCE. Equation is now balanced, as there are the same number hydrogen atoms (2) and the same number of chlorine atoms (2) on the products and reactant side.

Firstly you need an equation with the correct chemical formulae (in case of molecules the number of atoms in a molecule, in case of an ionic compound or giant covalent structures the ratio of atoms in the compound)………. You’ll probably be given this in the question Mg + O2  MgO Just like this one Then all you do is list the atoms that are involved on each side of the arrow Mg + O2  MgO Mg O

Mg + O2  MgO Mg + O2  MgO 2 Then start balancing: [1] Just count up the atoms on each side Mg + O2  MgO Mg O 1 1 2 1 [2] The numbers aren’t balanced so then add “BIG” numbers (stoichiometric factors) to make up for any shortages Mg + O2  MgO Mg O 1 2 2 2 2 And adjust totals

WE SAY THAT THE EQUATION IS BALANCED!! But the numbers still aren’t equal, so add another “BIG” number (stoichiometric factor) 2 Mg + O2  MgO Mg O 1 2 2 And adjust totals again NOW BOTH SIDES HAVE EQUAL NUMBERS OF ATOMS WE SAY THAT THE EQUATION IS BALANCED!!

Why didn’t anyone tell me it was so easy to balance equations???!!! GROUP ACTIVITY: Try to balance these equations using the same method You have 5 min! Why didn’t anyone tell me it was so easy to balance equations???!!! [1] Na + Cl2  NaCl [2] CH4 + O2  CO2 + H2O [3] Li + HNO3  LiNO3 + H2 [4] Al + O2  Al2O3

How did you get on?? Here are the answers: [1] 2 Na + Cl2  2 NaCl [2] CH4 + 2 O2  CO2 + 2 H2O [3] 2 Li + 2 HNO3  2 LiNO3 + H2 [4] 4 Al + 3 O2  2 Al2O3

Examples 2 2 2 2 3 4 2 2 2

3.3 Chemical equations As opposed to a word equation a chemical equation lists individual substances as their chemical formulae (in case of molecules the number of atoms in a molecule, in case of an ionic compound or giant covalent structures the minimum ratio of atoms in the compound). Since the chemical formulae give the number of atoms involved on both sides of the reaction, all atom counts should be balanced. Reason is that chemical reactions never destroy or create atoms, they are simply rearranged (by changing the state of their valence electrons)! Two types of numbers appear in a chemical equation: Word equation: Methane + Oxygen  Carbon dioxide + Water Chemical equation: CH4 + 2 O2  CO2 + 2 H2O The balancing of an equation is referred to as stoichiometry. The stoichiometric factors in a chemical equation should always be the smallest possible set of numbers (e.g. if you can divide all factors by 2, you should do so!) An index is part of the chemical formula and gives the number of an atom type within the compound A stoichiometric factor gives the number of molecules or ratio units in the reaction. This factor multiplies all following indexes when figuring the total number of atoms!