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Suppose I eat a whole $450~ \rm{g}$ chocolate Easter rabbit. The enthalpy of combustion of chocolate is $−22.4~\rm{ kJ/g}$. One kilogram of body fat contains $39000 ~\rm{kJ}$ of energy. Walking for an hour uses up $690 ~\rm{kJ}$ of energy.

For how many hours do I have to walk to use up the energy consumed?

So far I have calculated the energy found in $450 ~\rm{g}$ of the Easter bunny by multiplying $450~ \rm{g}$ by $-22.4 ~\mathrm{kJ/g}$. This gave me $-10080~ \mathrm{kJ}$.

I’m thinking my next step would be dividing $-10080 ~\mathrm{kJ}$ by $690 ~\mathrm{kJ}$ to find the answer. But I feel this is incorrect because I don’t understand the relevance of $1~\mathrm{kg}$ of body fat containing $39000 ~ \mathrm{kJ}$.

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  • $\begingroup$ I don't think the energy contained in body fat is of any relevance (just like you said). It may just be given to confuse the person attempting the question. $\endgroup$ Commented Mar 26, 2015 at 7:05

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As binary geek said, that information is not required in the calculations. Its probably given to make people realize that by gulping chocolate and walking for just 5-10 mins wont make you reduce your weight. Standard Satire has been employed!

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You must understand the extra information has nothing to do with any of your calculations. It is just there to throw you off although it is satirical. You must understand that if you feel that you have arrived at the right answer, and it makes sense, then there is no reason for you to second guess yourself, especially in Chemistry.

Thanks. :)

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