When octane (C8H18) is burned in air, it chemically reacts with oxygen gas (O2) to produce carbon dioxide (CO2) and water (H2O). What mass of water is produced by the reaction of 5.4g of oxygen gas?

Answer 1

The balanced equation for the combustion of Octane is:

2 C₈H₁₈ + 25 O₂ → 16 CO₂ + 18 H₂O.

From this equation you can see that the ratio of moles of O₂ to H₂O is 25:18. If you know how many moles of oxygen is consumed, multiplying it by 18/25 will give you the number of moles of water is produced. Since we know that 5.4 grams of O₂ is consumed, we can calculated the amount of water produced. 5.4g O₂ represents 5.4/32 moles of O₂, which is equal to 0.16875 moles of O₂.

Therefore, 18/25 • 0.16875 = moles of water produced = 0.1215 moles H₂O. Since the question asks the mass of water produced, we multiply by the molecular weight of water : 18 • 0.1213 = 2.187 grams of water.

Answer 2