Types of Chemical Reactions - Chemical Reactions and Equations, CBSE, Class 10, Science Video Lecture

At first glance these chemical reactions might
seem like a mess of information, but there
are patterns among them.
It’s helpful for chemists to sort all the
chemical reactions into categories so that
they can make predictions about how chemicals
might react.
There are five main types of chemical reactions:
combination which is also known as synthesis,
single replacement, double replacement, decomposition
and combustion.
Now, not every reaction falls perfectly into
one category, sometimes a reaction falls under
two categories.
But there are some key features to each category.
Let’s start with combination reactions.
Combination reactions combine the two or more
substances to form a new single substance.
This example is elemental magnesium and oxygen
combining to form magnesium oxide.
The two elements combined and formed one ionic
compound.
Even though it made two units of magnesium
oxide, they are the same substance.
So here we have the balanced chemical equation,
a particulate drawing of that same reaction
and now here’s a general equation for combination
reactions.
A + B yields substance AB.
The reverse version of this kind of reaction
is called decomposition.
In this reaction, things fall apart instead
of coming together.
A single substance breaks down into two or
more simpler products.
Here is an example of hydrogen peroxide breaking
down into water and oxygen.
Usually, decomposition reactions need heat,
or fire or electricity to get started.
This reaction can happen quickly with a catalyst
like yeast or manganese dioxide.
So we have the equation, a drawing and now
a simple formula for decomposition, AB yields
A plus B. The resulting compounds are smaller
and simpler than the starting compound.
Let’s look at the next type of reaction
Single Replacement.
In this reaction, one element replaces a second
element in a compound.
We’ll use the example of zinc reacting with
iron chloride to make zinc chloride and elemental
iron.
The two metals in this case, have swapped
places.
So here we have an equation, drawing and now
a simple formula for single replacement reactions,
A plus BC yields AC + B. But not all single
replacement scenarios actually work.
In order to see if the swap will occur, we
need to reference a chart the activity series
of metals.
The more active metals are toward the top
and the metals decrease in their activity
as you move to the bottom.
In the previous reaction, zinc was the individual
element and was higher than iron on the activity
series.
So this reaction occurred.
But if we tried to react elemental iron with
zinc chloride, nothing would happen, because
iron has a lower activity than zinc.
Now let’s look at the next type of reaction
Double Replacement.
This reaction is similar to single replacement
except we’re starting with two compounds.
the reaction has an exchange of positive ions
between the two compounds.
In This example copper(II) chloride and hydrosulfuric
acid swap their positive ions to make copper
sulfide and hydrochloric acid.
So here we have an equation, drawing and now
a simple formula for double replacement reactions,
AB plus CD yields AD + CB.
You can see from this equation that A and
C have switched places and those represent
the positive ions.
Usually a double replacement reaction creates
one of three products a precipitate, molecular
substance or a gas.In this double replacement
reaction, we started with two aqueous solutions
and end with aqueous hydrochloric acid but
solid copper sulfate.
This will sink, or precipitate to the bottom
of the container.
Another possible product would be a molecule.
In this example, we start with aqueous substances,
but one of the products is a liquid, the water
and the other product is still aqueous.
Lastly, another possible product from a double
replacement reaction is a gas.
Again, we start with aqueous substances, sodium
cyanide and sulfuric acid, but form a gas
as a product: poisonous hydrogen cyanide gas.
Don’t try this one at home, folks.
The last type of chemical reaction is a fun
one, combustion.
In combustion an element or compound, typically
a hydrocarbon, reacts with oxygen, often producing
heat or light.
So here is the combustion of a hydrocarbon,
called methane.
The combustion with a hydrocarbon will always
make water and carbon dioxide as products.
This makes predicting the products really
easy in this case!
So here we have an equation, drawing and now
a formula for the combustion of a hydrocarbon.
The x and y variables here provide a shortcut
for balancing the equation as well.
But not all combustion reactions happen with
hydrocarbons.The combustion of magnesium in
oxygen is both a combustion reaction AND a
combination reaction.
Remember, there are some reactions that can
fit more than one type of reaction.Thanks
for watching this episode of Teacher’s Pet,
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