Transcript Balancing equations: 1st …review what we already know. A formula is a representation of a molecule of an element or a molecule of a compound. O2 H 2

Balancing equations:
1st …review what we already know.
A formula is a
representation of
a molecule of an
element or a
molecule of a
compound.
O2
H 2 SO 4
The subscript
represents the
12
22
11 number of
atoms of a
12 atoms of carbon
particular
22 atoms of
element in the
hydrogen
molecule.
C H O
11 atoms of oxygen
H 2 SO
4
1 molecule of sulfuric acid
2 atoms of hydrogen
1 atom of sulfur
4 atoms of oxygen
If no subscript is
shown. An
understood
one is
indicated.
A coefficient is a
number in front of
a formula and
represents the
number of
molecules.
If no coefficient is
shown, one
molecule is
indicated.
2C 12 H 22 O 11
2 molecules of sucrose
24 atoms of carbon
44 atoms of hydrogen
22 atoms of oxygen
2 H 2  O 2  2 H 2O
Hydrogen
 oxygen  water
An equation is a sentence showing
what is happening in a chemical
reaction.
2 H 2  O 2  2H 2 O
The reactants are the substances
(elements or compounds) that will
react. They are on the left or starting
side.
2H
2
 O 2  2 H 2O
The products on the right side of the
equation are what are formed or are
produced during the reaction.
• Chemical reactions do not create or destroy atoms,
but only rearrange them
•Law of Conservation of Mass
–During a chemical reaction matter is neither created nor
destroyed
–There must be as many atoms of each type on the left side
of the equation as on the right side
• Proper coefficients are placed in
front of formulas to balance atoms
• Subscripts cannot be changed
–S8 + 8O2  8SO2
http://www.nisd.net/secw
w/science/sciencetaks/quiz23/mass%20qui
z.htm
5 questions about
conservation of mass.
Allow pop-ups to view
answers.
Balancing Chemical Reactions
1
1
N
+
O
--->
N
O
1
2
2
2
1x2
1
1x2
O
1x1
Reactants
Products
# Atoms
# Atoms
Element
N
1x2
2
2
2
These don’t match. So….
1
Balancing Chemical Reactions
N2 + O2 ---> N2O1
21
1x2
2x2
Element
N
O
1
1x2
21
1x2
2x2
1x1
2x1
Reactants
Products
# Atoms
# Atoms
4
2
4
21
Number of reactants equals number of products.
N2 + O2 ---> N2O
2, 1 ---> 2
2 diatomic nitrogens
and 1 diatomic oxygen become nitrous oxide or “laughing gas”.
To fix the Al
To fix the Cl
To fix the H
Balancing
Chemical
Reactions
6
2
3
1
2
1
Element
1
1
Reactants
Products
# Atoms
# Atoms
Al
12
21
H
1
6
6
16
6 3
Cl
2
To finish fixing the K and try out the CrO4
1
1
1
1
2
1
1
1
1
1
1
To fix both the
NO3 and the K
Which coefficients are needed to
balance this equation?
1
1
1
2
Reactants
Products
Element
# Atoms
# Atoms
Pb
1 Pb
1 Pb
N
2N
2N
O
10 O
10 O
K
2K
2K
Cr
1 Cr
1 Cr
3
1
1 1
To fix our Ag
3
1
1 1
To fix our Cl
1
1
Which coefficients are needed to
balance this equation?
1
To fix the Cl
3
1
1
1
1
Now we have 3 H’s
Which coefficients are needed to
balance this equation?
and 2 H’s
To fix the H
To fix the Cl
2
6
1
2
1
1
3
1
To fix the Al
Which coefficients are needed to
balance this equation?
To fix the Ca
Finishes up the balanced equation.
3
1
3
1
1
1 1
To fix the SO4
Check: Reactants
3Ca, 6O, 6H, 2Al, 3S and 12O
1
1
2
1
1 1
To fix the Al and the OH
Products: 3Ca, 3S, 12O, 2Al, 6O, 6H
Which coefficients are needed to
balance this equation?
Which one is already balanced
correctly?
The Al don’t match.
The H don’t match.
1
1
1x3 for S and
4x3 for O
Which one is already balanced
correctly?
Cl don’t match.
Al don’t match.
Cl don’t match.
http://www.creativechemistry.org.uk/gcse/revision/equations/0
2.htm
This hyperlink has you balance equations.
Instantly find out if you are correct or not.
As
+
NaOH
→
6
2
2 Na3AsO3 +
2
2
2
2
H2
4
1
2
3
1
4
1
2
3
4
1
4
6
3
2
3
?
2
2
1
2
2
When the above equation is balanced, the
coefficient for magnesium chloride is —
A0
B1
C2
D4
’04 Su #25
2
2
1
1
1 lead
2 oxygens
1 1
≠
1 lead
3 oxygens
What are the coefficients that will
balance this chemical equation?
A 2, 1, 1
B 3, 4, 2
C 2, 2, 1 2 lead
2 lead
=
4 oxygens
D 4, 3, 2 4 oxygens
Put a 2 here to make an even number of oxygens.
1 lead
2 oxygens
≠
2 lead
4 oxygens
’03 10 #45
2
2
1
2
1
1
1
1
Then we’ll need to put
coffecients on this side To make the hydrogens ‘even’,
We put the coefficient 2 here.
of the arrow to finish
And have a sum of 4 hydrogens,
balancing it out.
2 potassiums and 2 oxygens
2
What is the coefficient for H O
when the equation is balanced?
A1
B2
C3
D4
’03 11 #19
To produce 4 molecules of
sugar, a plant needs —
F 6 molecules of hydrogen
G 12 molecules of ATP
H 18 molecules of water
J 24 molecules of carbon dioxide
Multiply the whole reaction by 4.
4(
4 x 6 carbon dioxide
1
)
’03 10#10
Which chemical equation
supports the law of conservation
of mass?
4 hydrogens 1≠zinc
2 hydrogens 1 zinc
1 aluminum
2 oxygens 4 aluminums
2 oxygens
1
hydrogens ≠ 21hydrogens
3 carbons
carbon
F 2H2O(l) 1 2carbons
H2(g) +≠ O
(g)
1hydrogens
chlorine
23 chlorines
2
hydrogens
1 carbon
1 oxygen
3ZnCl
oxygens
G Zn(s) + HCl(aq)
2(aq) + H2(g)
4 hydrogens = 4 hydrogens
4 oxygens
oxygens
H Al4C3(s) +
H2O(l) 4 CH
4(g) + Al(OH)3(s)
J CH4(g) + 2O2(g)
CO2(g) + 2H2O(g)
’04 11 #32
The energy not stored in
the bonds of the carbon
dioxide and water must
have left in the form of
heat.
=≠
+
Reactants
=
+
Products
Why is the sum of the products’ energy in this
reaction less than the sum of the reactants’
energy?
A Energy is given off as heat.
B The products absorb available energy.
C Energy is trapped in the reactants.
D The reactants’ energy is less than the melting
point of glucose.
’04 11 #37
According to the law of conservation of
mass, how much zinc was present in
the zinc carbonate?
A 40 g
B 88 g
C 104 g
64
+
192
=
152
+
?
D 256 g
64 + 192 – 152 = ?
’03 11 #39
If all the reactants in a chemical reaction are
completely used, which of the following
statements accurately describes the
relationship between the reactants and the
Reactants become Products
products?
2H + O  2H O
2
2
2
20 grams + 10grams = 30 grams
F The products must have a different
physical state than the reactants.
G The total mass of the reactants must
equal the total mass of the products.
H The reactants must contain more complex
molecules than the products do.
J The density of the reactants must equal
the density of the products.
’04 Su #40
100 g
Reactants →
Products
The chemical equation shows CaCO3 being heated.
Which of these statements best describes the mass of
the products if 100 g of CaCO3 is heated?
A The difference in the products’ masses is equal to the
mass of the CaCO3.
B The sum of the products’ masses is less than the
mass of the CaCO3.
C The mass of each product is equal to the mass of the
CaCO3.
D The sum of the products’ masses equals the mass of
the CaCO3.
’04 11 #29
When 127 g of copper reacts
with 32 g of oxygen gas to form
copper (II) oxide, no copper or
oxygen is left over. How much
copper (II) oxide is produced?
F 32 g
127 + 32 = ?
G 95 g
H 127 g
J 159 g
’04 11 #40
After
The illustrations show a
conservation-of-mass
experiment. The solution in the
beaker lost mass because —
Some of the water
evaporated because of the heat.F materials have less mass at
high temperatures
G the mass of the reactants and
products was less than 100 g
H sodium sulfate (Na2SO4) is
lighter than air
J some of the water molecules
After( less
Before(100 g)
turned into gas
Before
than 100 g)
REACTANTS →Products The sum of the reactants = the sum of the products.
’0410#30
According to this information, what
is the chemical formula for
aluminum sulfate?
A AlSO4
B Al2(SO4)3
C Al3(SO4)2
D Al6SO4
’04 11 #23
+1 +2
+3 +4 -3 -2 -1 0
+1 +2
+3 +4 -3 -2 -1 0
Na P
Li C
+1 +2
+3 +4 -3 -2 -1 0
Na+1 P-3
Li C
+1 +2
+3 +4 -3 -2 -1 0
Na+1 P-3
3
1
Li C
+1 +2
+3 +4 -3 -2 -1 0
Na+1 P-3
3
1
Li C
+1 +2
+3 +4 -3 -2 -1 0
Na+1 P-3
3
1
Li C
+1 +2
+3 +4 -3 -2 -1 0
Balanced!
Na3P
Li C
+1 +2
+3 +4 -3 -2 -1 0
Na3P
Li+1C± 4
+1 +2
+3 +4 -3 -2 -1 0
Na3P
Li+1C± 4
4
1
+1 +2
+3 +4 -3 -2 -1 0
Na3P
Li+1C± 4
4
1
+1 +2
+3 +4 -3 -2 -1 0
Na3P
Li4C
Balanced!
According to this information, what
is the chemical formula for
aluminum sulfate?
A AlSO4
B Al2(SO4)3
C Al3(SO4)2
D Al6SO4
’04 11 #23
The chemical formula for
calcium chloride is —
F Ca2Cl
G CaCl
H CaCl2
J Ca2Cl3
’04 11 #38