|MadSci Network: Biochemistry|
Sorry about the delay on this one. I think what you are asking about here is the reverse of the enthalpy of formation of one gram of a mouse, or roughly the amount of heat released by the conversion of all the compounds in one gram of a mouse into their corresponding free elements in their most stable states. I will admit right now that their is no way I am going to calculate this out for you! However, I can show you the steps to an approximation, and you could extend that to the actual calculation if you want. You are right that most mammalian bodies are seventy percent water by weight. If we assume that the remaining thirty percent is composed of various hydrocarbon compounds, then we could approximate those hydrocarbons as methane (since that's the best one in the table that I have in front of me!). The molar enthalpy of formation of water is -285 kJ/mole, and the molar enthalpy of formation of gaseous methane (sorry, another approximation) is -75 kJ/mole. The minus sign means that heat is released upon their formation. Now you just have to figure out how many moles of water and hydrocarbon/methane there are in one gram of a mouse and calculate how much heat would be released or consumed by their formation, and the reverse of that is how many kJ there are in one gram of a mouse (approximately). Of course, you have to convert from joules to calories, too.
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