## HW #7.47 part B

cynthmartin
Posts: 4
Joined: Fri Sep 26, 2014 2:02 pm

### HW #7.47 part B

Hi! The only part that I do not understand of this question is why we multiply by 5471KJ/mol. Where did this come from and why do we multiply by it to get the KJ/year? Thanks !

Astred 1D
Posts: 15
Joined: Fri Sep 26, 2014 2:02 pm

### Re: HW #7.47 part B

Hi,

In the question it states that the enthalpy of combustion of gasoline can be approximated by that of octane. Since we are trying to find the yearly energy we need a value of energy when we are computing the yearly energy. In problem 7.45 it states that the enthalpy of combustion for octane is -5471kJ. You can use this value, because the problem said to approximate the combustion of gas with that of octane.

Hope this helps.

Justin Le 2I
Posts: 142
Joined: Fri Sep 26, 2014 2:02 pm

### Re: HW #7.47 part B

For these kinds of problems, one way to check if you have the right answer is to see what units your answer is and see if it makes sense. In the context of this question, the units kJ/year would be most appropriate so you would try and get your final answer with that unit.

Return to “Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)”

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