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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