2 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.
3 Coefficients are known as “multipliers” Whenever coefficients are written before a compound/element it is multiplied by EACH subscript.For example: 2 H2OThe TWO will now be multiplied by the “H” and “O”2 x H2 = FOUR2 x “O” (O, not a zero) = TWO* Remember no subscript indicates one atom.
4 Practice Coefficients and subscripts How many of each atom is present in this compound?NH3Nitrogen: __________________ Hydrogen: _____________________2 Li2CO3Lithium: ____________ Carbon: ___________ Oxygen: ___________3. How many of each atom is present in this compound?3 MgCO3
5 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 Fe2O P4 + 3 O2 2 P2O3
6 Na + O2 Na2O2 How to balance an equation? Step 1: Create a R.A.P tableWhat’s a R.A.P table ??R ReactantsA AtomP ProductComplete the “A” first.What are the different elements or atoms involved in this reaction?Then complete “R” and “P.”#R atom #P1Na22O2
7 Step 2. Go to the first atom that’s not balanced and balance it! Na + O2 Na2O2Sodium is not balanced. What can we do to balance them? Multiply the reactant by 2. CHANGE THE EQUATION!#R atom #P2x1Na22O22 Na + O2 Na2O2This is now balanced!
8 Some Equations may require multiple steps to complete. H2 + O2 H2O#R atom #PStart by creating the RAP table.2H2Oxygen is not balanced.What can you do balance it?2x2O1Multiply the product by 2.Currently your equation looks like this:H2 + O2 2 H2OThis is unbalanced. The product is a compound and if you multiply the Oxygen by 2, the number of Hydrogen atoms increase!
9 H2 + O2 2 H2O 2 H2 + O2 2 H2O Update the RAP table What can we do tobalance the number ofHydrogen atoms?#R atom #P2x2H42O2Multiply the reactant by 2.Your final answer should look like:2 H2 + O2 2 H2O