Predicting Reactions General Rules

1
Predicting ReactionsGeneral Rules
1. All reactions occur
2. Net ionic reactions only
3. Phases are not required aqueous by charge
4. Completely dissociated chemicals shown as
ions (i.e. strong acid is H A-)
5. All other dissociated chemicals shown as
complete compound (i.e. weak acid is HA)
1
2
Predicting ReactionsGeneral Rules (Pg 2)
6. Burned in air - means combustion in O2
7. Heated means decomposition
2
3
Predicting ReactionsMajor Types

• 1. Look for two uncombined elements (Syn.)
• 2. Look for single reactant (Decomposition)
• 3. Look for Combustion Reaction
• 4. Look for Acid-Base Reactions (DR)
• 5. Look for Two Salt Solution (Precip)
• 6. Look for REDOX Reaction
• 7. Look for water as Reactant
• 8. Look for Transitional metal and Ligands
  
  

3
4
Predicting Reactions

• 1. Looking for two uncombined elements (Syn)

A. Must put them together. Need sensible
oxidation
B. Example Solid sulfur is burned in oxygen
S O2 gt
SO2
C. Example A piece of solid zinc is heated in
chlorine gas
Zn
Cl2 gt
ZnCl2
4
5
Predicting Reactions

• 2. Look for single reactant (Analysis)

A. Only can break up into two or more product B.
Usually produces simple oxide and oxide gases
C. Example Solid calcium carbonate is heated.
CaCO3 gt
CaO
CO2
5
6
Predicting Reactions

• 3. Look for Combustion Reactions

A. Burned in air or oxygen is same
B. Always forms oxide gases I. C - CO or
CO2 II. H - H2O III. S - SO2 or SO3
C. Example Propane is burned in air
C3H8 O2 gt
CO2 H2O
D. Example Carbon disulfide is burned in air
CS2 O2 gt
CO2
SO2
6
7
Predicting Reaction

• 4. Looking for Acid-Base Reaction

A. Acid and Base
Be careful only strong acid strong
base give H OH- gt H2O
Weak acid/base cant get rid of other part
Example Solution of hydrofluoric acid sodium
hydroxide are mixed
(must keep F- )
HF
OH- gt
F-
H2O
7
8
Predicting Reaction

• 4. Looking for Acid-Base Reaction (Contd)

B. Acid/Base with salt of other
Remember Hydrolysis (salts breaking up into
ions)
Same as simple acid-base reaction
Example Soln of hydrochloric acid sodium
bicarbonate is mixed
H
HCO31- gt
H2CO3
Example Soln of potassium hydroxide ammonium
chloride mix.
OH-
NH3 H2O
NH41 gt
8
9
Predicting Reaction

• 4. Looking for Acid-Base Reaction (Contd)

C. Polyprotic acid Sulfuric acid
Polyprotic Only one H comes off or
on Exception Excess acid- goes all the way
Sulfuric acid - For now, assume both concentrated
dilute form completely dissociate
Example Equal volume of equimolar solutions
of phosphoric acid potassium
hydroxide are mixed
H3PO4
OH1- gt
H2PO41- H2O
Example Excess hydrochloric acid mixed w/soln
potassium sulfide
H
S2- gt
H2S
9
10
Predicting Reaction

• 5. Looking for Two Salt Solution

A. General Assumptions (Does not replace
solubility rules)
I. A salt containing (1- charge) anion is
SOLUBLE (dont forget solubility rules
especially AgCl)
II. A salt containing (2- or 3- charge) anion
INSOLUBLE (dont forget solubility rules
especially with sulfate)
Example A soln of silver nitrate is added to
potassium iodide soln
Ag
I1- gt
AgI (Remember reaction must occur)
10