When backpacking in the wilderness, hikers often boil water tosterilize it for d

Question

When backpacking in the wilderness, hikers often boil water tosterilize it for drinking. Suppose that you are planning abackpacking trip and will need to boil 36 L of water for yourgroup. What volume of fuel should you bring? Assumeeach of the following: the fuel has an average formula ofC7H16, 15% of the heat generated fromcombustion goes to heat the water (the rest is lost to thesurroundings); the density of the fuel is 0.78 g/ml, the initialtemperature of the water is 25.0 degrees C and the standardenthalpy of formation of C7H16is -224.4 Kg/mol. They are looking for V= ___ ml Thank you very much for your help. When backpacking in the wilderness, hikers often boil water tosterilize it for drinking. Suppose that you are planning abackpacking trip and will need to boil 36 L of water for yourgroup. What volume of fuel should you bring? Assumeeach of the following: the fuel has an average formula ofC7H16, 15% of the heat generated fromcombustion goes to heat the water (the rest is lost to thesurroundings); the density of the fuel is 0.78 g/ml, the initialtemperature of the water is 25.0 degrees C and the standardenthalpy of formation of C7H16is -224.4 Kg/mol. They are looking for V= ___ ml Thank you very much for your help. What volume of fuel should you bring? Assumeeach of the following: the fuel has an average formula ofC7H16, 15% of the heat generated fromcombustion goes to heat the water (the rest is lost to thesurroundings); the density of the fuel is 0.78 g/ml, the initialtemperature of the water is 25.0 degrees C and the standardenthalpy of formation of C7H16is -224.4 Kg/mol. They are looking for V= ___ ml Thank you very much for your help.

Explanation / Answer

Heat required to boil the water                    =Heat required to raise temperature from 25 to 100 C + heat requiredto boil at 100 C                     ={ 36,000 g * 4.18 J/(g.C) * (100-25) C * (1 kJ / 103 J)} + { 2000 moles * 40.79 kJ/mol}                     =11286 + 81580                     =92866 kJ
I understand the equation for heat (q) is mass*Cs of water*Change in temp, which is up to here:                                                                                        q ={ 36,000 g * 4.18 J/(g.C) * (100-25) C * (1 kJ / 103J) } but why do you have to add  { 2000 moles *40.79 kJ/mol}? Where did this equation comefrom? And how did they get the number40.79kJ/mol? Clarify this part for me please.

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