Some chemical reactions of organic compounds
3 marks · NormalPentane burns completely in oxygen. Write the balanced chemical equation for the complete combustion of pentane ([31m\ce{C5H12}[0m)), and state the type of reaction. Show your working.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
\ce{C5H12(l) + 8O2(g) -> 5CO2(g) + 6H2O(l)}; combustion
Also accept: \ce{C5H12 + 8O2 -> 5CO2 + 6H2O}
Common mistakes: Incorrect balancing of oxygen; Stating addition or substitution instead of combustion
Show mark scheme and worked solution
Marking points
M1 · 1 mark · Correctly writes the unbalanced equation for pentane combustion.
A1 · 1 mark · Balanced chemical equation: C5H12 + 8O2 → 5CO2 + 6H2O.
B1 · 1 mark · States that the reaction is combustion.
Worked solution
Step 1: Write unbalanced equation:
Step 2: Balance carbon (5 atoms):
Step 3: Balance hydrogen (12 atoms):
Step 4: Count oxygens on product side: 5×2 + 6×1 = 10 + 6 = 16 O atoms. Therefore, 8 O2 molecules needed on reactant side.
This reaction is combustion, as pentane reacts with oxygen to form carbon dioxide and water.