How can I balance synthesis reactions?

1 Answer
May 10, 2014

A synthesis reaction is is the combining of two single elements into a compound. This can be accomplished either as an ionic or molecular coupling in the pattern

#A + B -> AB#

We will look at two examples of synthesis, first the formation of Ammonia #NH_3# and the oxidation of iron to form rust.

To produce ammonia the basic equation is

#N + H -> NH_3#

We must remember that Nitrogen and Hydrogen are both diatomic molecules in their standard gas form. This adjusts the equation to

#N_2 + H_2 -> NH_3#

Now we need to adjust coefficients in order to balance the atoms on each side of the equation. Currently we have 2 atoms of nitrogen and 2 atoms of hydrogen on the reactant side and 1 atom of nitrogen and 3 atoms of hydrogen on the product side.

We can balance the hydrogens by placing a coefficient of 2 in front of ammonia and a coefficient of 3 in front of the hydrogen.

#N_2 + 3H_2 -> 2NH_3#

This gives us 6 hydrogen on each side and coincidentally the nitrogens now equal 2 on each side.

The equation is balanced.

In the case of the formation of Rust #Fe_2O_3#

The basic equation is

#Fe + O -> Fe_2O_3#

We are reminded that Oxygen is a diatomic and adjust the equation to

#Fe + O_2 -> Fe_2O_3#

We now see 1 iron and 2 oxygen as reactants and 2 iron and 3 oxygen as products. We can balance the oxygen by placing a 2 coefficient in front of rust and a 3 coefficient in from of the oxygen to get 6 oxygen atoms on each side.

#Fe + 3O_2 -> 2Fe_2O_3#

Since iron has only one atom on the reactant side we must use the coefficient 4 to balance the iron to 4 atoms on each side. To balance the final equation.

#4Fe + O_2 -> Fe_2O_3#

I hope this was helpful.