Balancing Chemical Equations What goes in must come out!

What is the Law of Conservation of Mass? In the reaction N2 + 3H2 2NH3 If 14 grams of N2 reacted with 3 grams of H2, how many grams of ammonia would be produced?

Law of Conservation of Mass You need to remember this law! The Law of Conservation of Mass states: that mass is neither created nor destroyed in any chemical reaction. Therefore balancing of equations requires the same number of atoms on both sides of a chemical reaction. The number of atoms in the Reactants must equal the Number of atoms in the Products

Do these reactions abide by the Law of Conservation of Mass? YES!

Balancing Chemical Equations Balancing a chemical equation is much like the work of an accountant who has to show every penny that comes in and where it has gone to.

In order to balance equations, we first must remember…. How to count atoms! CO2 6CO2 C atoms= 6 O atoms= 6 x 2= 12 C atoms= 1 O atoms= 2 8Mg(NO3)2 Mg atoms= 8 N atoms= 8 x 1 x 2= 16 O atoms= 8 x 3 x 2= 48

Practice Problems #2a-e! Git er done!

How many of each? 2 2 4 4 2 2 Balanced? ___Yes ___No a. 2Na + 2H2O  2NaOH + H2 Reactants Products Na H O 2 2 4 4 2 2 Balanced? ___Yes ___No

How many of each? 1 1 1 2 2 1 Balanced? ___Yes ___No c. NaCl + F2  NaF +Cl2 Reactants Products Na Cl F 1 1 1 2 2 1 Balanced? ___Yes ___No

Practice Problems #3a-e

Balancing Equations 2 3 ___ Al(s) + ___ Br2(l) ---> ___ Al2Br6(s)

Balancing Equations Try this one! ___ CH4 + ___ O2 ---> ___ CO2 + ___H2O

CH4 + 2O2 ---> CO2 + 2H2O

Mg + O2  MgO Mg + O2  MgO 2 [1] Just count up the atoms on each side [2] The numbers aren’t balanced so then add “BIG” numbers to make up for any shortages Mg + O2  MgO Mg O 1 2 2 2 2 And adjust totals

WE SAY THAT THE EQUATION IS BALANCED!! But the numbers still aren’t equal, so add another “BIG” number 2 Mg + O2  MgO Mg O 1 2 2 And adjust totals again NOW BOTH SIDES HAVE EQUAL NUMBERS OF ATOMS WE SAY THAT THE EQUATION IS BALANCED!!

Try to balance these equations on WS D. 6(p Try to balance these equations on WS D.6(p.4 of your packet) using the same method: [1] H2 + O2  H2O [2] Mg + O2  MgO [3] Ca + H2O  Ca(OH)2 + H2

Try to balance these equations on WS D. 6(p Try to balance these equations on WS D.6(p.4 of your packet) using the same method: [1] 2H2 + O2  2H2O [2] 2Mg + O2 2MgO [3] Ca + 2H2O  Ca(OH)2 + H2

Steps to Balance Equations: Balance elements that appear only once on each side of the arrow. Next balance elements that appear only once on each side but have different numbers of atoms. Finally balance elements that are in two formulas in the same side.

Example NH3 + O2 NO + H2O Reactants Products N appears once on both sides in equal numbers, so the coefficient for NH3 is the same as for NO.

Example: NH3 + O2 NO + H2O Next look at H which appears only once on each side but has different numbers of atoms, 3 on the left and 2 on the right. The least common multiple of 3 and 2 is 6, so rewrite the equation to get 6 atoms of H on both sides: 2NH3 + O2 NO + 3H2O

Example: 2NH3 + O2 NO + 3H2O There are 2 oxygen atoms on the left and 5 on the right — the least common multiple of 2 and 5 is 10, so rewrite the equation as: 2NH3 + 5O2 4NO + 6H2O

Now count the atoms on each side: 2NH3 + 5O2 4NO + 6H2O Write them out keeping them on the appropriate side of the chemical equation 2 N (nitrogen atoms) 4 N (nitrogen atoms) 6 H (hydrogen atoms) 12 H (hydrogen atoms) 10 O (oxygen atoms) 10 O (oxygen atoms) This shows the equation not to be balanced “YET”

Check the number again: If you double the N and H on the left the equation will be balanced: 4NH3 + 5O2 4NO + 6H2O

Double-check: 4NH3 + 5O2 4NO + 6H2O The equation is Balanced 4 N (nitrogen atoms) 4 N (nitrogen atoms) 12 H (hydrogen atoms) 12 H (hydrogen atoms) 10 O (oxygen atoms) 10 O (oxygen atoms) The equation is Balanced