Welcome to the video common types of oxidation reduction reactions. There are
four common types of oxidation reduction reactions: combination, decomposition,
displacement, and combustion. Combination reactions. Combination
reactions occur when two reactants combine to form one product. A good
example is the reaction of magnesium with air.
Two combination reactions actually occurred when the magnesium was ignited
in air. Magnesium reacted with both the oxygen and nitrogen gases. These are the
two reactions.
Which reactant in reaction 1 is oxidized?
Magnesium is oxidized. It's oxidation number changed from zero to plus two.
For the reaction with oxygen, the oxidation step is seen below.
And this is the reduction step:
To balance the equation the oxidation half-reaction is multiplied by 2 so
that 4 negative electrons are produced to equal the 4 negative electrons
used in the reduction half-reaction. This equation is seen below.
And this is the reduction step:
Cancelling the electrons gives the balanced equation.
For the reaction with nitrogen, the oxidation step is the same. And this is
the reduction step. To balance the equation, the oxidation
half-reaction is multiplied by 3 so that 6 negative electrons are produced
to equal the 6 negative electrons used in the reduction half-reaction. This
equation can be seen below. And this is the reduction step.
Then we combine the ions
and cancel the electrons which gives the balanced equation seen below.
Decomposition reactions. Decomposition reactions occur when one
reactant decomposes to form two products.
A good example is the reaction of mercury II oxide to give elemental mercury and oxygen.
This reaction can be seen below. Which ion is reduced in this reaction?
Mercury 2 plus is reduced. Its oxidation number changed from +2 to 0.
This is the reduction half-reaction.
This is the oxidation half-reaction. We multiply the reduction step by two
and add the half reactions and cancel the electrons.
Displacement reactions.
Displacement reactions occur when one element
displaces another element from a compound during a chemical reaction.
A good example is the reaction of sodium with water.
This is the chemical equation for this reaction.
Which reactant is oxidized in this reaction?
Sodium is oxidized. Its oxidation number changed from zero to plus one.
This is the oxidation half-reaction.
This is the reduction half-reaction. We multiply the oxidation step by two
and add the balanced half-reactions and cancel the electrons.
If a larger piece of sodium is added to water,
the heat generated from the displacement reaction causes a second reaction to occur.
Hydrogen combines with
oxygen to form water.
The displacement reaction has the same equation as before. This is seen below.
This is the combination reaction. This latter reaction occurs in the gas phase
and the energy released during the reaction takes the form of heat and light.
It produces a flame.
Combustion reactions. Combustion reactions occur when a substance reacts
with oxygen. Usually with the rapid generation of heat to produce a flame.
A good example is the reaction of hydrogen with oxygen seen below.
Which molecule is reduced in this reaction?
Oxygen is reduced. The oxidation number of oxygen changed
from zero to minus two. Now you will have an opportunity to test your knowledge by
classifying the following reactions. For each one, determine if it is a
combination, decomposition, displacement, or combustion reaction.
Feel free to pause the video at any point if you need more time.
How would you classify this reaction?
This is a combination reaction because there are two reactants combining to
form one product.
How would you classify this reaction?
This is a decomposition reaction. Decomposition occurs when one reactant
decomposes to form two products. And finally, how would you classify this
reaction?
This is a displacement reaction. Displacement reactions happen when one
element displaces another element from a compound during a chemical reaction.
Congratulations! You have completed this video: Common types of oxidation
reduction reactions.