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? asked in Science & MathematicsChemistry · 2 months ago

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

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

Update:

must be in three sig figs

Update 2:

I have no idea how to do this stuff

Update 3:

Please help

1 Answer

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  • ?
    Lv 5
    2 months ago

    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) 

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