Balancing Chemical Equations

Law of Conservation of Mass In a chemical reaction, matter can neither be created nor destroyed. So, however many atoms of each element you have on the left side with the reactants… is same number of atoms of each element you will have on the right side with the products. They will simply be rearranged.

Parts of Chemical Equations Element Symbols means “yields” 16Rb + S8  8Rb2S Coefficients Subscripts Reactants Products

H2 + O2  H2O Balanced? +  H ___ O ___ 2 H ___ O ___ 2 2 1 Draw your atoms of hydrogen and oxygen. Then draw your molecule of water. Now take an inventory: H ___ O ___ 2 H ___ O ___ 2 2 1 Balanced? Nope, now what?

+  H O The molecules themselves cannot be changed but there must be the same number of each type of atom on each side of the yields sign (the arrow) in order to be balanced. When adding a coefficient to the equation, it will multiply the number of each type of atom in that formula.

H2 + O2  H2O 2 +  Now we have: H ___ O ___ 2 H ___ O ___ 2 4 Still not balanced! 2 1 2

2 H2 + O2  H2O 2 TaDa!! +  Now we have: 4 H ___ O ___ 2 H ___ O ___ 1

Na + MgCl2  NaCl + Mg +  Na ___ Mg ___ Cl ___ 1 Na ___ Mg ___ Cl ___ Not balanced

Na + MgCl2  NaCl + Mg 2 Na Cl Mg Cl Na + Mg +  Na Cl With 2 Cl’s on the reactant side, we want to make 2 Cl’s on the products side… Na ___ Mg ___ Cl ___ 1 2 Na ___ Mg ___ Cl ___ 1 Not balanced yet… Now we have: 1 1 2 1 2

2 Na + MgCl2  2 NaCl + Mg Na Cl Mg Cl Na + Mg +  Na Cl Na Now we need to even up our sodiums (Na’s) Na ___ Mg ___ Cl ___ 1 2 Na ___ Mg ___ Cl ___ 1 2 Take inventory: Yippee!! 1 1 2 1 2

CH4 + O2  CO2 + H2O  C ___ H ___ O ___ C ___ H ___ O ___ Not 1 1 Not balanced 4 2 2 3

CH4 + O2  CO2 + H2O 2  C ___ H ___ O ___ C ___ H ___ O ___ 4 Nope, 1 C ___ H ___ O ___ 1 4 4 Nope, not yet… 2 4 2 3

CH4 + O2  CO2 + H2O 2 2 WooHoo!!  C ___ C ___ H ___ H ___ O ___ 1 C ___ H ___ O ___ 1 4 2 4 WooHoo!! 2 4 3 4

Now try this one on your own… Al2O3 + H2  H2O + Al 3 3 2 Box off your formulas so you don’t mess with them! Inventory: We did it!! Al ___ O ___ H ___ 2 Al ___ O ___ H ___ 1 2 3 1 3 6 2 6 2

Fe + O2  Fe2O3 4 3 2 I think we’ve got it!! Fe ___ O ___ 1 4 Fe ___ 6 3 6 This one’s tricky—start with oxygen and use the lowest common denominator.

The End!