Ch. 11.2 Notes Balancing Chemical Equations

Key Vocabulary Coefficients: numbers in front of a formula used to balance chemical equations (BIG numbers) Example: 3 H2O - Here we have 3 mols of H2O

Subscripts: The small numbers in the bottom right of a formula Subscripts: The small numbers in the bottom right of a formula. Indicates how many of that atom in the compound. We DO NOT change these. Example: MgF2 - This molecule contains 1 Mg atom and 2 F atoms.

Skeleton Equation: Unbalanced chemical equation. - Now let’s try balancing!

Write a skeleton equation, this is NOT balanced Mg + O2  MgO STEP ONE: list the atoms that are involved on each side of the arrow Mg + O2  MgO Mg O

Mg + O2  MgO Mg + O2  MgO 2 STEP TWO: start balancing Just count up the atoms on each side Mg + O2  MgO Mg O 1 1 2 1 STEP THREE: The numbers aren’t balanced so add coefficients to balance Mg + O2  MgO Mg O 1 2 2 2 2 And adjust totals

This follows the Law of Conservation of Mass But the numbers still aren’t equal, so add another coefficient 2 Mg + O2  MgO Mg O 1 2 2 And adjust totals again NOW BOTH SIDES HAVE EQUAL NUMBERS OF ATOMS This follows the Law of Conservation of Mass

Try to balance these equations using the same method: [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 ***When you’re done, pair up with somebody at your table and grab a laptop.