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What is a Chemical Reaction?
In a chemical reaction
atoms are not gained or lost.
During the reaction, bonds in
the reactants are broken
and new bonds are formed to make the products.
The atoms have only swapped
partners and the
total number
of atoms is the same before and
after the reaction.
What is the Yield from a Chemical
Reaction?
There are three reasons why the mass of
the products
(called the yield) of a chemical
reaction
is not always the same as the mass of
the reactants.
1. You might lose some of the products
when you try to
separate
them
from the mixture after the reaction has finished.
2. The reaction may be reversible.
3. Some of the reactants may form different
products
from the ones you expect.
Some reactions form products which are not
useful.
These are called waste products and
they may be toxic
or difficult to dispose
of.
You can calculate
the maximum (theoretical)
yield
available from a reaction.
The actual yield that
you get can be compared to the maximum
to give a percentage yield.
For example, if the maximum yield for a reaction is
16·67
g
and the actual yield
is only 14·88 g, then the percentage
yield is
(14·88 ÷
16·67) x 100
= 89·3%.
The chemical industry
tries to find fast chemical
reactions
with a high percentage
yield and no waste products.
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