How does chemical equation balancing work?MY teacher was explaining this too fast and I could not understand, It would be nice if I could get a refreshment and a few examples along with it...

How does chemical equation balancing work?

MY teacher was explaining this too fast and I could not understand, It would be nice if I could get a refreshment and a few examples along with it inscribing about the different types of reactions. Ex: Single Replacement, Decomposition, Synthesis etc.

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ndnordic | High School Teacher | (Level 2) Associate Educator

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To balance a chemical equation, you first write the equation showing the reactants(s) on the left side of the equal sign, and the product(s) on the right side of the equal sign.  The reactants are always what you start with and the products are always what you end up with.

Now you can count the number of atoms of each element on the reactant side and the number of atoms of each element on the product side and make a table.  If there are the same number of atoms on each side, the equation is balanced; if not, it is unbalanced and it is your job make it balanced.

The most important rule in balancing is that you must not change the subscripts of any of the reactants or products.

So for example,

in the synthesis reaction between hydrogen and oxygen, water is produced.  The basic equation is:

H2 + O2 --> H2O

When you count atoms, you see 2 hydrogen and 2 oxygen on the left, but 2 hydrogen and only 1 oxygen on the right.

You CANNOT change the oxygen on the right to H2O2 because you are changing the product to a different compound.

So H2 + O2 --> H2O2 is wrong.

The only way you can balance a chemical equation is by the use of coefficients. Coefficients are placed in front of reactant(s) and/or product(s) to make the equation balanced. These coefficients tell you the number of moles of each material taking part in the chemical reaction.

Using the synthesis of water again:

H2 + O2 --> H2O

By inspection, you can see it is not balanced.

So since there are 2 oxygen on the left, you need 2 oxygen on the right.

H2 + O2 --> 2 H2O

Every time you add a coefficient to either side, you need to recount to see if you have the same number of atoms of each element on each side of the equation.

You now have 2 H and 2 O on the left, but 4 H and 2 O on the right.

So add a 2 in front of the H on the left.

2 H2 + O2 --> 2 H2O

Now when you count, you see you have equal numbers of each element on each side and the equation is balanced.

The second part of your question relates to the fact that all of the millions of possible chemical reactions can be of a few general types.

The general types are:

1. Synthesis, where the number of reactants is always greater than the number of products.

2. Decomposition, where the number of products is always greater than the number of reactants. Synthesis and decomposition are opposites of the same chemical equation.

Thus, 2H2 + O2 --> 2 H2O is a synthesis reaction, while 2 H20 --> 2 H2 + O2 is the complementary decomposition reaction.

3. Single replacement, where you have a element and a compound on the left, and a different element and a different compound on the right.  The general form is:  A + BX --> B  + AX

An example is:

2 NaCl + F2 --> 2 NaF   + Cl2

4. Double replacement, where you have two compounds on the left side, and two different compounds on the right side. Think of it as two couples at a dance, where they switch partners for one dance. The general form is:

AX + BY --> AY  + BX

An example is:

HCl   +  NaOH  -->  NaCl    +  HOH

5. Combustion, where you have a fuel plus oxygen on the left, and carbon dioxide and water as the products on the right.

An example is:

C3H8 (propane gas) + O2 --> CO2   + HOH

Balanced you would have:
C3H8  + 5 O2  --> 3 CO2  +   4 HOH

Sources:

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