Download H2, N2, O2, F2, Cl2, Br2, I2

CHEMISTRY 11
Mr. Bellman
Ch 9
Reactions
NOTES ON BALANCING EQUATIONS
NAME____________________
Date______________Bk_____
( 16 )
1. Don't forget the 7 diatomic elements, the HOFBrINCl 's, the big 7, the "gens". They are never by themselves in a chemical reaction
and they are paired in their elemental form:
H2, N2, O2, F2, Cl2, Br2, I2
2. Word equation:
hydrogen gas plus nitrogen gas produces ammonia gas
Skeleton / formula / chemical equation:
H2 (g)
Balanced equation
3 H2 (g)
Coefficient
It means:
+
+
N2 (g)
NH3 (g)
N2 (g)
2 NH3 (g)
subscript
state of matter
3 molecules of hydrogen plus 1 molecule of nitrogen produces 2 molecules of ammonia
3. • Only change the coefficient ( the number in front of the formula ) when balancing. This tells us how many of each molecule or
atom we have in the balanced equation. If there is no number in front, a " 1 " is there but we usually leave out the 1's.
• Do not change subscripts to balance. They are part of the molecular formula.
• States of matter may or may not be included and are not used in balancing. They just tell us a little more information about the
reaction.
(s) = solid
(l) = liquid
(g) = gas
(aq) = aqueous (dissolved in water)
4. Don't be surprised to see other elements in multiatomic form. Phosphorus is P4 and Sulfur is S8 in their elemental state. For
chem 11, just worry about the diatomic elements.
5. Make sure you can find total number of atoms using subscripts and coefficients. Multiply the numbers together.
eg.
C2H6 has 2 C atoms and 6 H atoms
3 C2H6 has 6 C atoms total and 18 H atoms total
Mg3(PO4)2 has 3 Mg atoms, 2 P atoms, and 8 O atoms
( or 2 ( PO4 ) groups )
2 Mg3(PO4)2 has 6 Mg atoms, 4 P atoms, 16 O atoms total
( or 4 ( PO4 ) groups )
Try: Determine the total number of each atom and the total number of polyatomic ion groups in the following:
2 S3O8
3 Na2CO3
4 (NH4)3P
2 Fe2(Cr2O7)3
TIPS TO HELP BALANCE EQUATIONS:
1. In balancing equations, leave elements by themselves until the end to help balance.
eg.
__ K
+
__ O2
__ K2O
(draw a picture if you have to)
2. Balance atoms in more than one formula and / or in elemental form last if possible.
___ C3H8
+
___ O2
___ CO2
+
___ H2O
3. Be able to write the formula ( skeleton / chemical ) equation from the word equation. Then balance.
sodium reacts with nitrogen to form sodium nitride
4. Double odd numbers on one side of the reaction to make them even for the other side if needed.
___ FeBr3
___ Fe
+
___ Br2
5. Keep polyatomic ions together as groups rather than splitting them up and counting. Put brackets around polyatomic ions to help.
___ Ba(OH)2 +
___ ScPO4
___ Ba3(PO4)2 +
___ Sc(OH)3
6. For acid / base neutralization reactions, try writing water ( H 2O ) as ( HOH ) to help balance.
___ H2SO4
+
___ Al (OH )3
___ Al2(SO4)3
+
___ HOH
7. If you end up with an odd number of atoms on one side and an even number of atoms on another, try doubling the balancing
work you have done so far.
___ C4H10
+
___ O2
___ CO2
+
___ H2O
8. Make sure you total all atoms when the formula might be written down a little different.
___ C3H7OH
+
___ O2
___ CO2
+
___ H2O
+
___ H2O
9. Some hydrate examples:
___ Mg(NO3)2 • 2H2O
___ Mg(NO3)2
In the next example, notice sulfate (SO4) does not occur on both sides so don't keep it together as a group. Must count separately.
___ CuSO4 • 3H2O
___Cu +
___ SO3
+
___ H2
+
___ O2
10. Well, then some are just plain hard. Look for clues to help balance. (see last question on wkst 2 for answer)
___ K2Cr2O7
+
___ HCl
___ KCl
+
___ CrCl3
+
___ H2O
+
___ Cl2
So now you know as much as I do about balancing equations. You are ready for the big leagues. Be careful. Have fun. Don't hurt
yourselves. Remember, safety is #1. Go on now and get your PhD in balancing equations and make your millions!!