When decane undergoes complete combustion, a mixture of carbon dioxide and water is formed - Edexcel - GCSE Chemistry Combined Science - Question 4 - 2016 - Paper 1

To balance the combustion reaction of decane (C₁₀H₂₂), we need to ensure that the number of carbon, hydrogen, and oxygen atoms on the reactants side equals those on the products side.

1. Count the number of carbon (C) atoms: In C₁₀H₂₂, there are 10 carbon atoms, so we will produce 10 CO₂: $$$$

ightarrow ext{10 CO}_2$$

2. Count the number of hydrogen (H) atoms: There are 22 H atoms, which will produce 11 water (H₂O) molecules (since each water molecule contains 2 H atoms): $$$$

ightarrow ext{11 H}_2 ext{O}$$

3. Balance oxygen (O) atoms: Now count the total number of oxygen atoms needed on the right side:

   • From 10 CO₂: 10 x 2 = 20 O
   • From 11 H₂O: 11 x 1 = 11 O
   • Total O needed = 20 + 11 = 31 O

   Since O₂ contains 2 O atoms, we need 15.5 O₂. Because we cannot have a fraction in a balanced equation, we will double all coefficients:

   $$$$

ightarrow 20 ext{CO}_2 + 22 ext{H}_2 ext{O}$$

Thus, the balanced equation for the complete combustion of decane is:

ightarrow 20 ext{CO}_2 + 22 ext{H}_2 ext{O}$$