Isooctane (c8h18; d = 0.692 g/ml) is used as the fuel during a test of a new automobile engine. how much energy (in kj) is released by complete combustion of 17.9 gal of isooctane to gases (δh o rxn = −5.44 × 103 kj/mol)? enter your answer in scientific notation.

ΔH o rxn = -2.23 x 10⁶ kJ

Explanation:

The reaction of combustion for isooctane is

C₈H₁₈ (l) + 9/2 O₂ (g)  8 CO₂ (g) + 9 H₂O (g)

with an enthalpy change of -5.44 x 10³ kJ/mol

So what we need is to calculate the number of moles that are the 17.9 gal to solve this question.

1 gal = 3.785 L ∴  17.9 gal x 3.785 L/ gal =  67.75 L = 67.5 x 1000 mL/L

= 6.78 x 10³  mL

d= m/ v   ∴ m= d  x v = 0.692 g/mL x 6.78 x 10⁴ g/1000 mL =  4.69 x 10⁴ g

Molecular Weight Isooctane is equal to 114.22 g/mol therefore  moles

n = 4.69 x 10 ⁴ g / 114.22 g/mol = 4.10 x 10² mol

and the heat of combustion for this number of moles will be given by

-5.44 x 10³ kJ/mol x 4.10 x 10² mol =  -2.23 x 10⁶ kJ

b is the correct