Download Balancing - Solon City Schools

Balancing Chemical
Equations
notes for p. 8-10
Balanced Equation

Atoms can’t be created or destroyed
 Law


of Conservation of Mass
All the atoms we start with we must end up with
A balanced equation has the same number of
each element on both sides of the equation
(reactant and product sides).
Counting Atoms
2H2 + O2 



product
Subscript: (numbers below)


Reactants 
2H2O
indicates how many atoms of an element.
Coefficient (numbers in front)


Indicates how many molecules/moles of a compound
(multiplies the number of atoms of each element in the
compound)
Chemical Formula
Counting up Atoms
Let’s Practice

NH3
_____ atoms of Nitrogen
 _____ atoms of Hydrogen
 _____ molecules/moles of NH3


NaCl
_____ atoms of Sodium
 _____ atoms of Chlorine
 _____ molecule/moles of NaCl

Practice

NH3
__1___ atoms of Nitrogen
 __3___ atoms of Hydrogen
 __1__ molecules/moles of NH3


NaCl
__1___ atoms of Sodium
 __1___ atoms of Chlorine
 __1___ molecule/moles of NaCl

Practice Again

8NaCl




3NH3




_____ atoms of Sodium
_____ atoms of Chlorine
_____ molecule/moles of NaCl
____ atoms of Nitrogen
____ atoms of Hydrogen
___ molecule/moles of NH3
Ca(NO3)2




_____ atoms of Calcium
_____ atoms of Nitrogen
_____ atoms of Oxygen
_____molecule/moles of Ca(NO3)2
Practice Again

8NaCl




3NH3




__8___ atoms of Sodium
__8___ atoms of Chlorine
__8___ molecule/moles of NaCl
__3__ atoms of Nitrogen
__9__ atoms of Hydrogen
__3_ molecules/moles of NH3
Ca(NO3)2





___1__ atoms of Calcium
___2__ atoms of Nitrogen
___6__ atoms of Oxygen
___1__molecule/moles of Ca(NO3)2
What if there is a coefficient of 2 in front of Ca(NO3)2 ?
More Practice

SO2 + 3H2O
_____ atoms of Sulfur
 _____ atoms of Hydrogen
 _____ atoms of Oxygen
 _____ molecule/moles of SO2
 _____ molecules of H2O

More Practice

SO2 + 3H2O
__1___ atoms of Sulfur
 __6___ atoms of Hydrogen
 __5___ atoms of Oxygen
 __1___ molecule/moles of SO2
 __3___ molecules of H2O

Let’s Step It Up a Little

2NH4NO3 + 3H2S
_____ atoms of Nitrogen
 _____ atoms of Hydrogen
 _____ atoms of Oxygen
 _____ atoms of Sulfur
 _____ molecule/moles of NH4NO3
 _____ molecule/moles of H2S

Let’s Step It Up a Little

2NH4NO3 + 3H2S
__4___ atoms of Nitrogen
 __14___ atoms of Hydrogen
 __6___ atoms of Oxygen
 __3___ atoms of Sulfur
 __2___ molecule/moles of NH4NO3
 __3___ molecule/moles of H2S

You Must Be Joking!

2Na2CO3 + 3CO2 + 4NaCl + Mg(NO3)2
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_____ atoms of Sodium
_____ atoms of Carbon
_____ atoms of Oxygen
_____ atoms of Chlorine
_____ atoms of Nitrogen
_____ atoms of Magnesium
_____molecules/moles of Na2CO3
_____ molecule/moles of CO2
_____ molecule/moles of NaCl
_____ molecule/moles of Mg(NO3)2
You Must Be Joking!

2Na2CO3 + 3CO2 + 4NaCl + Mg(NO3)2



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

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
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
__8___ atoms of Sodium
__5___ atoms of Carbon
__18___ atoms of Oxygen
__4___ atoms of Chlorine
__2___ atoms of Nitrogen
__1___ atom of Magnesium
__2___molecules/moles of Na2CO3
__3___ molecule/moles of CO2
__4___ molecule/moles of NaCl
__1___ molecule/moles of Mg(NO3)2
C




+
O
O

O C
O
Shows the reaction to form carbon dioxide
C + O2  CO2
This equation is already balanced
What if it isn’t already?
C





+
O
O

C
O
Shows the reaction to form carbon monoxide
C + O2  CO
We need one more oxygen in the products.
Can’t change the formula, because it describes
what is produced.
Remember, oxygen is a diatomic molecule.
C


+
O
O

C
O
C
O
The other Oxygen must be used to make
another CO
But where did the other C come from?
C
+
C


O
O

Must have started with two C
2 C + O2  2 CO
C
O
C
O
Rules for balancing
 Write the correct formulas for all the reactants
and products
 Count the number of atoms of each type
appearing on both sides
 Balance the elements (make them same amount
on reactant and product sides) one at a time by
adding coefficients (the numbers in front).
 Check to make sure it is balanced.
Never!


Change a subscript to balance an equation.

If you change the formula you are describing a
different reaction.

H2O is a different compound than H2O2
Never put a coefficient in the middle of a
formula

2 NaCl is okay, Na2Cl is not.
Example
H2 + O2  H2O
Make a table to keep track of where you
are at
Example
H2 + O2  H2O
R
P
2 H 2
2 O 1
Need twice as much O in the product
Example
H2 + O2 
R
P
2 H 2
2 O 1
Changes the O
2 H2O
Example
H2 + O2 
2 H2O
R
P
2 H 2
2 O 1 2
Also changes the H
Example
H2 + O2 
2 H2O
R
P
2 H 2 4
2 O 1 2
Need twice as much H in the reactant
Example
2 H2 + O2 
2 H2O
R
P
2 H 2 4
2 O 1 2
Recount
Example
2 H2 + O2 
2 H2O
R
P
4 2 H 2 4
2 O 1 2
The equation is balanced, has the same
number of each kind of atom on both sides
Example
2 H2 + O2 
2 H2O
R
P
4 2 H 2 4
2 O 1 2
This is the answer
Not this
Examples
+ O2  CO2 + H2O
 AgNO3 + Cu  Cu(NO3)2 + Ag
 Mg + N2  Mg3N2
 P + O2  P4O10
 Na + H2O  H2 + NaOH
 CH4
Examples
+ 2O2  CO2 + 2H2O
 2AgNO3 + Cu  Cu(NO3)2 + 2Ag
 3Mg + N2  Mg3N2
 4P + 5O2  P4O10
 2Na + 2H2O  H2 + 2NaOH
 CH4