The combustion of gasoline produces carbon dioxide and water. Assume gasoline to be pure octane (C8H18) and calculate how many kilograms of carbon dioxide are added to the atmosphere per 5.1 kg of octane burned. ( Hint: Begin by writing a balanced equation for the combustion reaction.)

15.7 kg of CO₂ are added to the atmosphere per 5.1 kg of octane burned

Explanation:

These are always the reactants in a combustion:

- O₂

- C₈H₁₈ (octane, in this case)

These are always the products in the combustion

- CO₂ and H₂O

The balanced reaction is: 2C₈H₁₈ +  25O₂  →  16CO₂ + 18H₂O

We assume the oxygen in excess, so the limting reactant is the octane.

We convert the mass to moles but first we need to convert the kg to g

5.1 kg . 1000 g / 1kg = 5100 g → 5100 g . 1 mol / 114g = 44.7 moles of octane

By stoichiometry, ratio is 2:16. Let's make a rule of three:

2 moles of octane produce 16 moles of dioxide

Therefore 44.7 moles of octane must produce (44.7  . 16) / 2 = 358 moles of CO₂

We convert the moles to mass (g), and finally we convert from g to kg

358 mol . 44g / 1mol = 15747 g → 15747 g. 1 kg / 1000g = 15.7 kg of CO₂

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