What mass of octane (in g) is required to produce 1240 kJ of heat?

Question

Octane (C8H18) is a component of gasoline that burns according to the following equation:

C8H18(l)+252O2(g)→8CO2(g)+9H2O(g)

ΔH∘rxn=−5074.1 kJ

Florine · Answer

Edit: Write down the dimensional analysis as I did. Just to clarify, I used "x" for multiplication and "/" to show division. All units should cancel except for grams, which makes sense because that's what you are solving for. I'm happy to give you the answer (to 3 sig figs) if you post what you get.

1240 kJ x (1 mol octane / 5074.1 kJ) x (1 mol octane / 114.23 g octane) = ___ g of octane.

I'll let you do dimensional analysis...

ΔH∘rxn=−5074.1 kJ
can be written as: ΔH∘rxn = 5074.1 kJ/mol
Molar mass octane: 114.23 grams
Reaction: C8H18 + 12.5 O2--> 8CO2 + 9H2O (not really needed)

What mass of octane (in g) is required to produce 1240 kJ of heat?

1 Answer