C6H8 + O2 ——à CO2 + H2O How many moles of O2 are needed to form 60 moles of CO2
Correct Answer: 80 moles of O2
To determine the number of moles of a reactant required to produce a specific amount of product, one must first ensure the chemical equation is balanced. A balanced equation adheres to the Law of Conservation of Mass, stating that atoms are neither created nor destroyed in a chemical reaction.
The initial, unbalanced equation is:
C6H8 + O2 → CO2 + H2O
Step 1: Balance the Chemical Equation
The first step is to balance the atoms on both sides of the reaction.
- Balance Carbon (C): There are 6 carbon atoms on the reactant side (in C6H8). To balance this, a coefficient of 6 is placed before CO2 on the product side.
C6H8 + O2 → 6CO2 + H2O - Balance Hydrogen (H): There are 8 hydrogen atoms on the reactant side. To balance this, a coefficient of 4 is placed before H2O on the product side (4 x 2 = 8 H atoms).
C6H8 + O2 → 6CO2 + 4H2O - Balance Oxygen (O): Now, count the oxygen atoms on the product side. There are (6 x 2) = 12 oxygen atoms in 6CO2 and (4 x 1) = 4 oxygen atoms in 4H2O, for a total of 16 oxygen atoms. To balance this, a coefficient of 8 is placed before O2 on the reactant side (8 x 2 = 16 O atoms).
The final, balanced equation is:
C6H8 + 8O2 → 6CO2 + 4H2O
Step 2: Use the Molar Ratio
This balanced equation provides the stoichiometric or molar ratio between the reactants and products. It shows that for every 8 moles of oxygen (O2) that react, 6 moles of carbon dioxide (CO2) are produced. This ratio is constant for this reaction:
8 moles O2 : 6 moles CO2
Step 3: Calculate the Required Moles
The problem requires finding the moles of O2 needed to form 60 moles of CO2. Using the molar ratio as a conversion factor, the calculation is set up to cancel the units of “moles CO2” and find “moles O2.”
Moles of O2 = (60 moles CO2) × (8 moles O2 / 6 moles CO2)
Moles of O2 = (60 × 8) / 6
Moles of O2 = 480 / 6
Moles of O2 = 80
Therefore, 80 moles of O2 are needed to form 60 moles of CO2.
