Question

A sample of octane undergoes combustion according to the equation 2 C8H18 + 25 O2 → 16 CO2 + 18 H2O ΔH°rxn = -11018 kJ. What mass of O2 (in grams) must react in order to generate 7280 kJ of energy?

Answer 1

`\large \boxed{\text{528.7 g} }`

Step-by-step explanation:

It often helps to write the heat as if it were a reactant or a product in the thermochemical equation.

Then you can consider it to be 11018 "moles" of "kJ"

We will need a chemical equation with masses and molar masses, so, let's gather all the information in one place.

M_r: 32.00

2C₈H₁₈ + 25O₂ ⟶ 16CO₂ + 8H₂O + 11 018 kJ

n/mol: 7280

1. Moles of O₂

The molar ratio is 25 mol O₂:11 018 kJ

`\text{Moles of O}_(2) = \text{7280 kJ} * \frac{\text{25 mol O}_(2)}{\text{11 018 kJ}} = \text{16.52 mol O}_(2)`

2. Mass of O₂

`\text{Mass of C$_(8)$H}_(18) = \text{16.52 mol O}_(2) * \frac{\text{32.00 g O}_(2)}{\text{1 mol O}_(2)} = \textbf{528.6 g O}_(2)\\\text{The reaction requires $\large \boxed{\textbf{528.67 g O}_(2)}$}`