Which of the following chemical reactions represents the combustion of propane (C3H8) in excess oxygen?

Question

Examoogle · Accepted Answer

The correct answer is Option A: C_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2O. The combustion of propane ($C_3H_8$) in excess oxygen is a complete combustion reaction. In this process, propane reacts with oxygen to produce carbon dioxide and water vapour, releasing a large amount of heat energy.

Step-by-Step Solution & Concepts:
The combustion of propane ($C_3H_8$) in excess oxygen is a complete combustion reaction. In this process, propane reacts with oxygen to produce carbon dioxide and water vapour, releasing a large amount of heat energy.

Working Principle: During complete combustion, hydrocarbon molecules react with an abundant supply of oxygen ($O_2$). All carbon atoms are oxidized to carbon dioxide ($CO_2$) and all hydrogen atoms are oxidized to water ($H_2O$). Balancing the chemical equation for propane requires 5 molecules of oxygen to yield 3 molecules of carbon dioxide and 4 molecules of water.

Key Formulas: $C_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2O$ — Balanced equation for complete combustion of propane

Key Points: Complete combustion requires excess or sufficient oxygen supply.; The products of complete combustion of a hydrocarbon are always carbon dioxide and water.; Combustion reactions are exothermic, releasing substantial thermal energy.

Advantages: High energy release and clean burning compared to heavier hydrocarbons when excess oxygen is present.

Disadvantages: Produces carbon dioxide, a greenhouse gas contributing to global warming.

Applications: LPG (Liquefied Petroleum Gas) cylinders used for domestic cooking and heating.; Portable camping stoves and gas heaters.

Additional Info: Standard enthalpy of combustion for propane is highly negative, indicating an exothermic reaction.. Option B represents incomplete combustion producing carbon monoxide, Option C yields pure carbon (soot), and Option D has an unbalanced stoichiometric coefficient for oxygen and water.

Answer: A is correct — The balanced chemical equation for the complete combustion of propane in excess oxygen is $C_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2O$.

Exam Tip: Always verify that both mass and atomic species are conserved on both sides of a chemical equation before selecting an option in exam questions.

Examoogle · Answer

Option B: C_3H_8 + 3O_2 \rightarrow 3CO + 4H_2O

Examoogle · Answer

Option C: C_3H_8 + 2O_2 \rightarrow 3C + 4H_2O

Examoogle · Answer

Option D: C_3H_8 + 4O_2 \rightarrow 3CO_2 + 2H_2O

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