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

a. energy is absorbed in the reaction.

if in a given reaction the energy of products is greater than the energy of reactants it means that reaction is endothermic and during the reaction, the energy is absorbed by reactants. in an endothermic reaction, the products have more stored chemical energy than the reactants. and in this reaction the reactants are more stable than products before the compounds with less energy are always more stable.