The document discusses three types of chemical reactions: combination reactions, combustion reactions, and decomposition reactions. It provides examples of each type of reaction and notes the key characteristics to look for in identifying them. Combination reactions involve two or more reactants forming one product. Combustion reactions involve a fuel reacting with oxygen to produce oxides. Decomposition reactions involve one reactant breaking down into two or more products.

1. 10/4/2010
Combination
Combustion
Decomposition
Combination Reactions
• A + B AB
• A and B can be elements or compounds!
• What to look for
– 2 or more separate reactants, forming 1 product
1

2. 10/4/2010
• Some of these reactions will have links to
watch videos
• Products of metal and non-metal – often you
can determine formula from group # or typical
charge
Zn + I2 ZnI2
The reaction is exothermic, the
Heat released sublimes the excess
Elemental iodine!!
The reaction requires a bit of water
To “catalyze” or initiate the reaction
Zinc metal is silvery, iodine is magenta crystals, the zinc iodide in a white salt
Zinc always forms +2 ions so ZnI2 is expected to be the product
2

3. 10/4/2010
Dropping flakes of
Antimony, a “semi-metal”
Into chlorine gas initiates
An energetic reaction
As evidenced by the
“sparks”
H2 + Cl2 2 HCl
This reaction is
Initiated by
light from
Burning Mg and
Produces an explosion
3

4. 10/4/2010
Note: properties change – iron is magnetic – but iron(III) sulfide is not!!
Na + Cl2 2 NaCl
This reaction also
Needs to be initiated with
Water
4

5. 10/4/2010
Combustion reactions
• All of us should be familiar with combustion
– Using a charcoal grill C + O2 CO2
– Using a butane lighter C4H10 + O2 CO2 + H2O
– Using a “gas” grill C3H8 + O2 CO2 + H2O
– Driving a gasoline car C8H18 + O2 CO2 + H2O
• The common thread in all these reactions is
elemental oxygen (O2) – they all produce heat
and light
• PS – the above equations are not necessarily
balanced – can you balance them??
Combustion reaction
• Reaction with oxygen
• A + O2 AO (also could be combination)
• AB + O2 AO + BO
• What to look for – oxygen (O2) as a reactant,
all products are oxides
5

6. 10/4/2010
Combination/Combustion example
• H2 from Zn/HCl rx balloon
• Clear away all combustible, have a wash bottle
ready
• Add energy (reaction is not spontaneous at
room temperature)
• Light wooden splint, hold with crucible tongs
• Touch bottom of balloon – be ready!
Combination products
• Metal + non-metal: use typical charges!!! For
product!!!
6

7. 10/4/2010
Combustion or combination
Combustion
7

8. 10/4/2010
Note –more than one product, oxygen part of both products, O2 is
a reactant
Complete combustion of carbon containing compounds produces CO2 not CO
Combination/Combustion
• O2 is a reactant and product contains O
• 2+ reactants, 1 product
8

9. 10/4/2010
Or combination!!!
O2
MgO
Mg
Note,Mg+2 smaller, O-2 larger than elemental
Atoms!!!
9

10. 10/4/2010
Decomposition
• AB -> A + B
• What to look for : 1 reactant, 2 or more
products
Decomposition example
• Catalytic decomposition of hydrogen peroxide
(H2O2)
• ½ full test tube hydrogen peroxide
• Add ~ ½ t yeast
• Mix with glass stirring rod
• What happens, what is produced?
10

11. 10/4/2010
Hydrogen peroxide decomposition
• H2O2(aq) H2O(l) + O2(g)
• Catalyst – catalase, peroxidase – found in blood,
radishes, red beets, potatoes!
• You can try this reaction – get a slice of raw
potato, radish or red beet and pour a few drop of
hydrogen peroxide (3%) on it – do you see
bubbles --- you may have used this on cut with
the same effect!!
• Note demonstration with higher concentration
11

12. 10/4/2010
2 NI3 N2 + 3I2
2 H2O 2 H2 + O2
Need electrolyte!!
12

13. 10/4/2010
2 HgO Hg + O2
HgO Hg
Heat applied cinnabar
13