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

To balance the equation for the complete combustion of decane (C₁₀H₂₂), we can follow these steps:

1. Write the unbalanced formula: $2C_{10}H_{22} + O_2 \rightarrow CO_2 + H_2O$

2. Determine the products of combustion: both carbon dioxide and water.

3. Count the number of atoms:

   • Carbon: 20 from C₁₀H₂₂ (10 x 2)
   • Hydrogen: 44 from C₁₀H₂₂ (22 x 2)

4. Balance carbon first:

   • Since there are 20 carbon atoms from decane, we need 20 CO₂: $2C_{10}H_{22} + O_2 \rightarrow 20CO_2 + H_2O$

5. Balance hydrogen next:

   • There are 44 hydrogen atoms, which would yield 22 H₂O: $2C_{10}H_{22} + O_2 \rightarrow 20CO_2 + 22H_2O$

6. Count oxygen:

   • On the right side, we have 20 CO₂ contributing 40 oxygen atoms and 22 H₂O contributing 22, totaling 62 oxygen atoms.
   • The equation thus requires: $O_2 \text{ on the left: } (62/2 = 31)$

7. Finally, the balanced equation is: $2C_{10}H_{22} + 31O_2 \rightarrow 20CO_2 + 22H_2O$