Question

Write a balanced equation for the decomposition of ammonium nitrate to form molecular nitrogen, molecular oxygen, and water. Explain your answer.

Answer 1

The unbalanced reaction is

a NH₄NO₃   ⇒   b N₂ + c O₂ + d H₂O

where a, b, c, and d are unknown constants.

Count how many times each element appears on either side of the reaction.

• reactants:

N = 2a, H = 4a, O = 3a

• products

N = 2b, O = 2c + d, H = 2d

Now we solve the system of equations,

2a = 2b … … … [1]

4a = 2d … … … [2]

3a = 2c + d … … … [3]

From [1] we immediately have

a = b

In [2], we get

2a = d

and substituting for d in [3] gives

3a = 2c + 2a

a = 2c

Let c = 1; then

• a = 2×1 = 2

• b = 2

• d = 2×2 = 4

So, the balanced reaction is

2 NH₄NO₃   ⇒   2 N₂ + O₂ + 4 H₂O