Chemical Reactions Chapter 10

Chemical Equations N2 + 3H2 -> 2NH3 N2 + H2 -> NH3 coefficients tell the number of molecules in a reaction N2 + H2 -> NH3 subscripts tell the number of atoms in a molecule

Chemical Equations N2 + 3H2 -> 2NH3 N2 + 3H2 -> 2NH3 The products are on the: RIGHT SIDE N2 + 3H2 -> 2NH3 The reactants are on the: LEFT SIDE

Chemical Equations N2 + 3H2 -> 2NH3 N H Law of Conservation of Mass: Mass can not be created or destroyed. Therefore: the number of atoms of each element must be the same on both sides of the equation. How many Nitrogens does each side have? How many Hydrogens does each side have? 2 2 6 6

Balancing Chemical Equations How do we balance a chemical equation? We use the scoreboard method N2 + 3H2 -> 2NH3 N H Our goal is to have both sides be even. In other words, our goal is to TIE! 2 2 scoreboard 6 6

Chemical Equations H2 + O2  H2O H O Is it balanced? We need to add coefficients to make it balanced Is it balanced now? 2 2 4 2 2 4 2 1 2

Chemical Equations Fe + O2  Fe2O3 Fe O 4 3 2 4 1 2 4 6 2 3 6

Chemical Equations FeCl3 + KOH  KCl + Fe(OH)3 Fe Cl K OH Here, OH is a polyatomic ion, so we leave it as OH on our scoreboard 3 3 1 1 3 1 3 3 3 1 1 3 1 3

Chemical Equations C3H6 + O2  CO2 + H2O C H O 2 9 3 6 6 3 6 3 1 3 6 in some reactions, where the O is split between two compounds, save it for last, and write it as two separate numbers We now have an odd number of oxygens. Double the organic molecule and rebalance. 2 9 3 6 6 3 6 3 1 3 6 12 6 2 6 12 18 2 2 + 1 6 3 12 6

Now you practice. Pick a partner and work on your Balancing Practice Worksheet. Be sure to show your scoreboards!