Question

How many moles of oxygen are required to completely combust 1 mole of propane (C\(_3\)H\(_8\))?

• A. 4 moles
• B. 5 moles
• C. 6 moles
• D. 3 moles

Hint:

Use the shortcut \(x + y/4\) to quickly find the moles of \(O_2\) for any hydrocarbon \(C_xH_y\). For propane: \(3 + 8/4 = 3 + 2 = 5\).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept
Complete combustion of a hydrocarbon involves reacting it with oxygen (\(O_2\)) to produce carbon dioxide (\(CO_2\)) and water (\(H_2O\)). To find the molar ratio, we must write a balanced chemical equation.

Step 2: Key Formula or Approach
The general formula for the combustion of a hydrocarbon \(C_xH_y\) is: \[ C_xH_y + \left(x + \frac{y}{4}\right)O_2 \to xCO_2 + \frac{y}{2}H_2O \]

Step 3: Detailed Explanation
1. For Propane, \(x = 3\) and \(y = 8\). 2. Carbon balancing: 3 atoms of C produce \(3CO_2\). 3. Hydrogen balancing: 8 atoms of H produce \(4H_2O\). 4. Oxygen balancing: - From \(CO_2\): \(3 \times 2 = 6\) oxygen atoms. - From \(H_2O\): \(4 \times 1 = 4\) oxygen atoms. - Total Oxygen atoms needed = \(6 + 4 = 10\). - Since oxygen exists as \(O_2\), the number of moles of \(O_2\) is \(10 / 2 = 5\). 5. Balanced Equation: \[ C_3H_8 + 5O_2 \to 3CO_2 + 4H_2O \]

Step 4: Final Answer
5 moles of oxygen are required to combust 1 mole of propane.