combination combustion decomposition
DESCRIPTION
TRANSCRIPT
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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
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• 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
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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
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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
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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
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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!!!
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Combustion or combination
Combustion
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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
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Or combination!!!
Mg
O2
MgO
Note, Mg+2 smaller, O-2 larger than elemental
Atoms!!!
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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?
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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
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2 NI3 � N2 + 3I2
2 H2O � 2 H2 + O2Need electrolyte!!
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2 HgO � Hg + O2
HgO
cinnabarHg
Heat applied