Chapter 8
Chemical Reactions
Balancing Equations &
Types of Chemical Reactions
GCC
CHM 130
8.1 Chemical Reactions
Is this a chemical
or physical change?
Phys
Is this a chemical
or physical change?
Chem
What are four signs a chemical reaction may have occurred?
1 A precipitate forms
3 Energy is released or absorbed
2 A gas forms w/o heating
4 A permanent color change
Review
• What is the difference between a chemical
change (reaction) and a physical change?
A physical change does NOT change the molecule –
no bonds are broken, often just the state of matter
changes. A chemical reaction DOES change the
molecule into a different one.
8.2 Chemical Reactions
• Reactants g Products
• Balanced – same atoms on both sides
• Remember to include physical states
(s) = solid
(l) = liquid
(g) = gas
(aq) = aqueous solution (dissolved in water)
8.3 Remember
• Which elements are solid, liquid, gas
• Which are diatomic
• Matter can not be created or destroyed so
reactions must be balanced
• Subscripts tell how many atoms in that
molecule H2O
• Coefficients tell how many molecules
3 H2O
Write the balanced chemical reaction
A = Blue
B = Red
3 A2 + B2 g 2 A3B
Draw and Balance These
N2 (g) +
H2 (g)
+
CO (g) +
H2 (g) 
NH3 (g)
Br2 (l) 
HBr (g)
O2 (g) 
CO2 (g)
N2 (g) + 3 H2 (g)  2 NH3 (g)
H2 (g) + Br2 (l)  2 HBr (g)
2 CO (g) + O2 (g)  2 CO2 (g)
How to Balance a Rxn
1. Write the unbalanced chemical reaction
with proper
formulas first
Ex: Sodium reacts with chlorine to
produce solid sodium chloride.
Na (s)
+
Cl2 (g)
g
Why Cl2 not just Cl???
If Cl is diatomic, why
not NaCl2?
NaCl (s)
Cl is diatomic !!!
Diatomic is only when
elements are alone, does
not apply to compounds.
2. Now change the coefficients
never the subscripts till balanced.
Count polyatomic ions as a group,
don’t count the atoms.
Answer:
2 Na (s)
+
Cl2 (g)
g 2 NaCl (s)
Why can’t we change the subscripts?
Write the reaction:
Hydrogen reacts with oxygen to form water vapor.
H2 (g) +
O2 (g)
g
H2O (g)
Now balance and use the lowest possible
numbers. (Like reducing a number)
You FIRST write the reaction with
PROPER FORMULAS, once that is
done you can NOT change the
subscripts. Then you can balance
by adding coefficients.
Writing a reaction from words
• Write then balance the reaction of
phosphorus being heated with oxygen gas to
make solid diphosphorus pentaoxide.
P (s) + O2(g) g P2O5(s)
4 P (s) + 5 O2(g) g 2 P2O5(s)
There are many in the end of chapter
problems like this to practice.
Hard Practice Prob – do at home
I’ll give answers next class (remind me)
• Write then balance this reaction: aqueous nickel(III)
sulfate plus lead(II) nitrate produces nickel(III) nitrate
and solid lead(II) sulfate
Ni2(SO4)3 (aq) + Pb(NO3)2 (aq) g Ni(NO3)3 (aq) + PbSO4 (s)
Ni2(SO4)3 (aq) + 3 Pb(NO3)2 (aq) g 2 Ni(NO3)3 (aq) + 3 PbSO4 (s)
8.4 Types of Chemical Reactions
8.5 Combination Reactions: 2 reactants form one product
A + X g AX
8.6 Decomposition: one reactant forms 2 or more products
AX g A
+
X
Combustion: burning with O2 to form carbon dioxide and steam
C xH y
+ O2(g)
g CO2 (g) +
H2O (g)
8.8 Single Replacement: metal A becomes part of an ionic cmpd
A + BX g AX + B
8.10 Double Replacement Reactions: switch partners
BY (aq) g AY (aq)
AX (aq) +
+
BX (s)
8.11 Neutralization Reactions: acid + base form water and salt
HA(aq)
+
MOH(aq) g H2O (l) +
MA(aq)
8.5 Combination Reactions
Balance: P (s)
2 P (s)
+ O2 (g)
+ 2 O2 (g)
→
→
P2O4 (g)
P2O4 (g)
8.6 Decomposition Reactions
Balance:
Fe2O3 (s)
2 Fe2O3 (s)
→
→
Fe (s)
4 Fe (s)
+
+
O2 (g)
3 O2 (g)
Combustion Reactions
Write then balance the
combustion of Propane gas,
C 3H 8
C3H8 (g) + O2 (g) g CO2 (g) + H2O (g)
C3H8 (g) + 5 O2 (g) g 3 CO2 (g) + 4 H2O (g)
Combustion Reactions
We are only doing simple hydrocarbon
(CxHy) combusion reactions. So…
Products are always CO2(g) + H2O(g)
And
O2(g) is always a reactant
You should be able to predict the
products for these !!!
8.7 Activity Series
• Given to you on Periodic Table
• Most active WANTS to be cation (+ charge) in
compound with a buddy (social)
• Least active WANTS to be alone as neutral
element metal with zero charge (loner)
8.9 Solubility Rules
Solubility Rules
Generally soluble compounds with:
1. Li+, Na+, K+, NH4+ (ALWAYS!)
2. C2H3O2-,
3. NO34. Halide ions (X), Cl-, Br-, I- BUT AgX, Hg2X2, HgX, PbX2 insoluble
4. SO42- BUT SrSO4, BaSO4,
, PbSO4 are all insoluble
Generally insoluble compounds with:
6. CO327. CrO428. PO439. S2- BUT CaS, SrS, BaS soluble
10. OH- BUT Ca(OH)2, Sr(OH)2, and
Ba(OH)2 soluble
Soluble means dissolves in water.
NaCl(aq) which is Na+ and Cl- ions in water
Insoluble means does not or very little dissolves in water.
AgCl(s)
Drawings!
Draw these chemicals in beakers of water.
LiNO3
MgS
Ca(OH)2
KI
BaCO3
Soluble is (aq), insoluble is (s)
Write (aq) or (s) by each.
Al(OH)3(s)
Ca(NO3)2 (aq)
Sr(OH)2 (aq) (NH4)2CO3(aq)
K2S (aq)
Li3PO4 (aq)
PbI2 (s)
Ba(C2H3O2)2 (aq)
Now for practice let’s NAME these compounds!
CuS
(s)
Electrolytes
• Electrolytes are solutions that contain ions
• Strong electrolytes are good conductors, ionic
compounds that are soluble (completely dissolves into
ions) are these. You will learn later that strong acids
and bases are strong electrolytes.
• Weak electrolytes are weak conductors, ionic
compounds that are insoluble are these. Insoluble =
only a few dissolve into ions. You will learn later that
weak acids and bases are weak electrolytes.
• Non-electrolytes are solutions that do not conduct at
all, zero ions. Covalent chemicals are often nonelectrolytes.
• http://www.youtube.com/watch?v=1XWnovm6JLs&feature=related
8.8 Single Replacement Reactions
1. Look at the two metals or H, which is more active?
2. Most active wants to be in compound, if it already is
then No Reaction (NR), if not switch partners.
3. Write the correct product formulas – the elemental
state is always charge 0
4. Write the states for the products. (s, l, g, aq)
5. Last is balance.
Zn(NO3)2 (aq) + Na (s)
→ ?
Zn(NO3)2 (aq) + 2 Na (s) → 2 NaNO3 (aq) + Zn (s)
Why not Na(NO3)2???
Na is +1 and NO3 is –1 so
they already balance out,
don’t need 2
Solid Metal + Acid
If a metal is more active than H, then H2 gas produced.
(You must write the products 1st, then the states, then
balance last)
Al (s) + HCl (aq)
g
Al (s) + HCl (aq) g
Al (s) + HCl (aq) g
?
AlCl3 (?) + H2 (?)
AlCl3 (aq) + H2 (g)
2 Al (s) + 6 HCl (aq) g 2 AlCl3 (aq) + 3 H2 (g)
Active Metals
http://video.google.com/videoplay?docid=-3103610687149839311#
http://www.youtube.com/watch?v=OFG4Yr7lQzw
Active Metals Series: Li > K > Ba > Sr > Ca > Na
The six active metals will react with water
to produce hydrogen gas and the metal hydroxide.
M (s)
+
H2O (l)
→
H2 (g)
+
MOH
Write the reaction and balance (You must write the products 1st)
1. Cu (s) + H2O(l) g NR
2. Ba (s) + 2 H2O(l) g H2 (g) + Ba(OH)2 (aq)
17.1 Oxidation and Reduction
• Single Replacement reactions are a type of
REDOX reaction where oxidation and
reduction occur. (Note you can’t have one
without the other)
Oxidation Numbers
• Ox # = fancy name for charge
• All elements in natural state = 0
• When in a compound, charge is + for metals
and – for nonmetals depending on how many
electrons lost or gained
• Variable charge metals range from +1 to +9 in
rare cases.
Nomenclature worksheet has this info online
Review CHARGES!!!
http://web.gccaz.edu/~ksmith8/rev130.htm
17.2 Oxidation
• Losing electrons, charge goes ______________
UP
• Cu(s) g Cu2+ (aq) + 2 e• Solid Cu is oxidized (OX = UP)
• What is oxidized = reducing agent
• What elements like to lose electrons?
metals
Reduction
DOWN
• Gaining electrons, charge goes ______________
• S (s) + 2 e- g S2- (aq)
• Solid sulfur is reduced
• What is reduced = oxidizing agent
• What elements like to gain electrons?
nonmetals
Redox Reactions
• Must have one chemical oxidized AND another
reduced. Can’t have one w/o the other.
• What is oxidized and reduced are always reactants,
the products are the result of the redox.
• So if asked “what is ox or red?”, answer is reactant
chemicals.
• When you answer, answer the whole compound, not
just the element that changed charges.
• You have to figure out the charges!!!
Easy example
Cu+2 (aq) + Fe(s) g Cu(s) + Fe+2(aq)
Cu went from +2 to 0 so charge down = reduced
Fe went from 0 to +2 so charge up = oxidized
What is oxidized?
What is reduced?
What is oxidizing agent?
What is reducing agent?
Fe (s)
Cu+2 (aq)
Cu+2(aq)
Fe(s)
What is oxidized, reduced,
ox agent, and red agent???
Co(NO3)3 (aq) + Pt (s) g Pt (NO3)3 (aq) + Co(s)
•
•
•
•
•
Co charge went from +3 to 0
Pt charge went from 0 to +3
So Co(NO3)3 is reduced (cobalt(III) nitrate)
Pt(s) is oxidized
Co(NO3)3 is oxidizing agent
• Pt(s) is reducing agent
What is oxidized, reduced? What is the ox
agent, red agent?
Ca(s) + NiCl2 (aq) g CaCl2(aq) + Ni(s)
Ox = solid Ca NOT Ca2+ or CaCl2
Red = NiCl2 (aq) for fun what is the name?
Ox Agent = NiCl2 (aq)
(nickel(II) chloride)
Red Agent = Ca(s)
Do the redox practice problems in the online
notes !!! AND there is a worksheet online for
redox.
8.10 Double Replacement Reactions
Precipitation is a type of DR Rxn and a solid forms
AX (aq) +
BY (aq) → AY (s) + BX (aq)
Identify the solid then balance.
1. Ba(NO3)2 (aq) + MgSO4 (aq) → BaSO4 (s)
2. Pb(NO3)2 (aq) +
3. BaCl2 (aq) +
2 KI (aq) → PbI2 (s)
2 AgNO3 (aq)
+ Mg(NO3)2 (aq)
+
→ Ba(NO3)2 (aq)
2 KNO3 (aq)
+ 2 AgCl (s)
8.11 Neutralization Reactions
Another type of DR Reaction
HA
Acid
+
MOH →
Base
H2O +
MA
Products are usually water
and ionic compound.
Write the products, the states, and THEN balance.
2
HCl (aq) + Ba(OH)2 (aq) g
2
H3PO4 (aq) + 3Ca(OH)2 (aq) g Ca3(PO4)2 (s) + 6 H2O (l)
2 H2O (l) + BaCl2 (aq)
Summary
• Know how to use solubility rules and draw ionic
compounds in beakers of water
• Recognize strong vs weak electrolytes
• Recognize and balance
– Combination
– Decomposition
– Double displacement - precipitation
• Recognize, write products, and balance
– Single displacement
– Acid base neutralization
– Combustion
• Identify what is oxidized, reduced and the agents in a
redox reaction
You REALLY should do the
worksheets for chapter 8 on the
Worksheet website
http://web.gccaz.edu/~ksmith8/rev130.htm
Self Tests
• Page 230 Ch. 8 Try 1-5, 7-9, 11-16
• Page 510 Ch. 17 Try 1-2
• Answers in Appendix J