need chemistry help

Question

How many milligrams of oxygen are required to create 5.17 liters of carbon dioxide gas at STP from the complete combustion of methane (CH4) Give answer in scientific notation.

Answer 1

The reaction for the combustion of methane is given

CH₄ + O₂ →CO₂ + H₂O

CH₄ + O₂ →CO₂ + 2H₂O (balance hydrogen)

CH₄ + 2O₂ →CO₂ + 2H₂O (balance oxygen to balance equation)

Thus two moles of oxygen gas is needed to produce 1 mole of carbon dioxide gas.

Note that at STP, one mole of an ideal gas occupies 22.4L by Avogadro's law.

Thus 5.17liters of carbon dioxide at STP = 5.17/22.4 = 0.231 moles of carbon dioxide.

Twice as many moles of oxygen is needed so twice 0.231 = 0.462 moles of oxygen is needed

Thus the number of grams of oxygen needed is 2 times 16 times 0.462 = 14.8g = 14,800milligrams of O₂.