Question

which answer best describes what is happening in the following reaction?
2c₈h₁₈ + 25o₂ → 16co₂ + 18h₂o
this is not a redox reaction. it is an example of combustion.
this is a redox reaction in which octane (c₈h₁₈) is the reducing agent.
this is a redox reaction in which carbon dioxide (co₂) burns due to ignition.
this is not a redox reaction, because a solution of carbon dioxide and water results

Explanation:

1. First, analyze the reaction type: The reaction $\ce{2C8H18 + 25O2 -> 16CO2 + 18H2O}$ is a combustion reaction (burning of octane in oxygen). Combustion reactions are also redox reactions.

• In $\ce{C8H18}$, carbon has a negative oxidation state (since it is bonded to hydrogen, which is less electronegative). In $\ce{CO2}$, carbon has a +4 oxidation state. So carbon is oxidized (oxidation state increases from negative to +4).
• In $\ce{O2}$ (oxidation state 0), oxygen is reduced to -2 in $\ce{CO2}$ and $\ce{H2O}$.

1. Now, analyze each option:

• Option 1: Incorrect. Combustion reactions are redox reactions (due to electron transfer/oxidation state changes).
• Option 2: Correct. Octane ($\ce{C8H18}$) is oxidized (carbon's oxidation state increases), so it acts as the reducing agent (a reducing agent is oxidized in a redox reaction).
• Option 3: Incorrect. $\ce{CO2}$ does not burn; the reactant being burned is octane ($\ce{C8H18}$), not $\ce{CO2}$.
• Option 4: Incorrect. As established, this is a redox reaction (oxidation state changes for C and O), and the product is not a "solution of carbon dioxide and water" in the context of the reaction type description here (the reaction is a combustion, not about forming an aqueous solution).

Answer:

B. This is a redox reaction in which octane ($\ce{C8H18}$) is the reducing agent.