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Atomic Structure

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. The total number of
atoms (the mass) 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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