Balancing Equations

Subscripts and coefficients The subscript indicates how many of each kind of atom exists. There is no subscript written if there is only one atom. For example, H2O. There are two hydrogen atoms and ONE oxygen. Coefficients tell us how much of the molecule we have. The product of the equation below indicates it has TWO water (H2O) molecules.

Coefficients are known as “multipliers” Whenever coefficients are written before a compound/element it is multiplied by EACH subscript. For example: 2 H2O The TWO will now be multiplied by the “H” and “O” 2 x H2 = FOUR 2 x “O” (O, not a zero) = TWO * Remember no subscript indicates one atom.

Practice Coefficients and subscripts How many of each atom is present in this compound? NH3 Nitrogen: __________________ Hydrogen: _____________________ 2 Li2CO3 Lithium: ____________ Carbon: ___________ Oxygen: ___________ 3. How many of each atom is present in this compound? 3 MgCO3

Law of Conservation of mass The law of conservation of mass states that matter can neither be created or destroyed This means the reactants and products of an equation must be equal; otherwise it is considered unbalanced. Is this balanced? 1. C + H4  CH4 2. Fe + Cl2  FeCl3 3. Fe + O2  Fe2O3 3. 1 P4 + 3 O2  2 P2O3

Na + O2  Na2O2 How to balance an equation? Step 1: Create a R.A.P table What’s a R.A.P table ?? R  Reactants A  Atom P  Product Complete the “A” first. What are the different elements or atoms involved in this reaction? Then complete “R” and “P.” #R atom #P 1 Na 2 2 O 2

Step 2. Go to the first atom that’s not balanced and balance it! Na + O2  Na2O2 Sodium is not balanced. What can we do to balance them? Multiply the reactant by 2. CHANGE THE EQUATION! #R atom #P 2x 1 Na 2 2 O 2 2 Na + O2  Na2O2 This is now balanced! 

Some Equations may require multiple steps to complete. H2 + O2  H2O #R atom #P Start by creating the RAP table. 2 H 2 Oxygen is not balanced. What can you do balance it? 2x 2 O 1 Multiply the product by 2. Currently your equation looks like this: H2 + O2  2 H2O This is unbalanced. The product is a compound and if you multiply the Oxygen by 2, the number of Hydrogen atoms increase!

H2 + O2  2 H2O 2 H2 + O2  2 H2O Update the RAP table What can we do to balance the number of Hydrogen atoms? #R atom #P 2x 2 H 4 2 O 2 Multiply the reactant by 2. Your final answer should look like: 2 H2 + O2  2 H2O

P4 + O2 → P4O10 #R atom #P

Al2O3 --> Al + O2 #R atom #P

Fe + H2O --> Fe3O4 + H2 #R atom #P

H2O2 --> H2O + O2 #R atom #P

Na2SO4 + CaCl2 --> CaSO4 + NaCl #R atom #P

N2 + H2 --> NH3 #R atom #P

Fe + H2O --> Fe3O4 + H2 #R atom #P

H2O2 --> H20 + O2 #R atom #P