Transcript Balancing Equations - Geneva Area City Schools

Balancing Equations
Balancing, Writing, and Naming
Equations
A.
word equation
1.
a word equation is written out in words
e.g. copper + oxygen ----> Copper oxide
2.
really is not useful
B.
Chemical equations
1.
involves chemical symbols
e.g. H2 + O2 ----> H2O (not balanced)
2.
C.
much more useful
must represent the facts
H2 + O2 ----> H2O
not
H2 + O2 ----> H2O2
D.
E.
make sure you always use the correct symbols
and follow the law of conservation of mass
Sodium is Na not S
Law of conservation of mass - in a chemical
reaction - mass can not be created nor
destroyed
-what you start with, you must also end with
Balancing equations
F.
1.
steps
a.
write down the correct symbols for the
elements
b. reactants go on the left products on the right
reactants
the
c.
products
is read as yields or equals
remember your 7 diatomics
H2, O2, N2, F2, Cl2, Br2, I2
d.
balance electrically (use subscripts) .
must do first
e.
balance by law of conservation of mass use coefficients.
Balancing Equations
Balancing Equations
 N2


+ H2
Nitrogen + hydrogen
NH3
ammonia
Count atoms

Reactants: 2 atoms N and 2 atoms H
Products:
1 atom N and 3 atoms of H
Balancing Equations
Nothing is balanced.
 Balance the nitrogen first by placing a
coefficient of 2 in front of the NH3.

 N2
+ H2
2NH3
Balancing Equations
N2 + H2

2NH3
Hydrogen is not balanced.
Place
a 3 in front of H2.
N2 + 3H2
Reactant
Product
2NH3
side: 2 atoms N, 6 atoms H
side: 2 atoms N, 6 atoms H
Balancing Equations
Ca3(PO4)2 + H2SO4
CaSO4 + H3PO4
Balancing Equations
 Side
note on Ca3(PO4)2
The subscript after the phosphate
indicates two phosphate groups.
 This means two PO43- groups with
two P and eight O atoms.

Balancing Equations


In this equation, the ion groups do not
break up.
Instead of counting individual atoms, ion
groups may be counted.
Ca3(PO4)2 + H2SO4
CaSO4 + H3PO4
Balancing Equations
Ca3(PO4)2 + H2SO4


CaSO4 + H3PO4
Reactants: Ca2+ – 3, PO43- - 2, H+ – 2,
SO42+ - 1
Products: Ca2+ - 1, SO42- - 1, H+ - 3, PO43-1
Balancing Equations


Balance the metal first by placing a
coefficient of 3 in front of CaSO4.
Products: Ca – 3 atoms, SO42- - 3 groups
Ca3(PO4)2 + H2SO4
3CaSO4 + H3PO4
Balancing Equations
Ca3(PO4)2 +3 H2SO4
3CaSO4 +2 H3PO4
Three sulfate groups are needed on the
 A coefficient of 2 placed in front of
reactant side so place a coefficient of 3 in
H3POof4 which
front
H2SO4. balances both hydrogen
and
phosphate.
 3H2SO4 gives 6 H+ and 3 SO42-.
 Neither phosphate nor Hydrogen is
balanced.

Balancing Equations
 Balancing
 Balance
hints:
the metals first.
 Balance the ion groups next.
 Balance the other atoms.
 Save the non ion group oxygen and
hydrogen until the end.
K2O + H2O
---> 2 KOH
2 H2O2 --->2 H2O + O2
3
4
2 Al + 3 O2
C7H16 + 11 O2
---> 2 Al2O3
--->7 CO2
+ 8 H2O
2 Na2O2 + 2 H2O --->24 NaOH + O2
SiO2 + 4 HF
C + H2O
---> SiF4
+ 2 H2O
---> CO + H2
2 KClO3 ---> 2 KCl
+ 3 O2
2 H3AsO4 ---> As2O5 + 3 H2O
4 KClO3 ---> 3 KClO4 + KCl
Al2(SO4)3 +3 Ca(OH)2 --->2 Al(OH)3 + 3 CaSO4
P4O10
+ 6 H2O
FeCl3 + 3 NH4OH
---> 4 H3PO4
---> Fe(OH)3 + 3 NH4Cl
4 Sb + 3 O2
---> Sb4O6
2 Ca3(PO4)2 + 6 SiO2 ---> P4O10 +6 CaSiO3
C3H8 + 5 O2
---> 3 CO2
+ 4 H2O
N2O5 + H2O
---> 2 HNO3
Fe2O3 + 3 CO
---> 2 Fe + CO2
2 Al + 6 HCl
---> 2 AlCl3 + 3 H2
2 PCl5
+ 8 H2O
6 H3BO3
---> H4B6O11
8 H2S + 8 Cl2
3 Mg
3 Fe
--->10 HCl + 2 H3PO4
+
N2
+ 4 H2O
2 NaOH + Cl2
---> S8 +
==>
==>
+ 7 H2O
HCl
16
Mg3N2
Fe3O4
+ 4 H2
==> NaCl + NaClO + H2O
Na2CO3 + 2 HCl ==> 2 NaCl
+ H2O + CO2
PHASE
II
Sodium sulfate + Barium chloride  sodium chloride + barium sulfate
First write the equation – make sure the charges are
Balanced(subscripts)
+
-2
Na SO4
2
+2
+ Ba Cl
-1
2
+1 -1
 2 NaCl
+2
-2
+ BaSO4
Next balanced according to the Conservation of Mass
(coefficients )
Copper(I) Phosphate + Barium Sulfate ---> Copper(I) sulfate + Barium Phosphate
Cu3PO4
+ BaSO4 Cu2SO4
+ Ba3(PO4)2
Calcium phosphate + Aluminum sulfate => Calcium sulfate + Aluminum phosphate
Lithium Acetate + Ammonium Carbonate => Lithium Carbonate + Ammonium Acetate
Calcium Carbonate ----->
Calcium Oxide + Carbon Dioxide
Hydrogen chloride + Iron (III) sulfate -> Iron (III) chloride + hydrogen sulfate
Iron(III) sulfite + mercury(I) carbonate ===>Iron (III) carbonate + Mercury(I)
sulfite
copper(I) dichromate + zinc nitrate ===> copper(I) nitrate + Zinc dichromate
copper(I) dichromate + zinc nitrate ==> copper(I) nitrate+ Zinc dichromate
Sodium + water ==> sodium hydroxide + hydrogen
Practice





Ca(OH)2 + H3PO4  H2O + Ca3(PO4)2
Cr + S8  Cr2S3
KClO3(s) Cl(g) + O2(g)
Solid iron(III) sulfide reacts with gaseous
hydrogen chloride to form solid iron(III)
chloride and hydrogen sulfide gas.
Fe2O3(s) + Al(s)  Fe(s) + Al2O3(s)
Types
of chemical reactions
Composition
– putting things together
2H2 + O2  2 H2O
Decomposition
– tearing things apart
2KClO3  3KCl + 2 O2
Single
replacement - one element replaces
the other
2Na Cl + F2 2 NaF
Double
+ Cl2
replacement – positive and negative ions
switch place
NaBr + KCl  NaCl + KBr
Meaning





A balanced equation can be used to
describe a reaction in molecules and
atoms.
Not grams.
Chemical reactions happen molecules at a
time
or dozens of molecules at a time
or moles of molecules.
Balancing Equations
This method of
balancing
equations is the
inspection
method.
 The method is
trial and error.
 Practice.

Chemical Equations






Are sentences.
Describe what happens in a chemical
reaction.
Reactants  Products
Equations should be balanced.
You should not be able to sleep knowing
there are unbalanced chemical equatins
Have the same number of each kind of
atoms on both sides because ...
Abbreviations




(s) solid
(g) gas
(aq) in water
heat

D

catalyst