When backpacking in the wilderness, hikers often boil water to sterilize it for

Question

When backpacking in the wilderness, hikers often boil water to sterilize it for drinking. Suppose that you are planning a backpacking trip and will need to boil 40 of water for your group. What volume of fuel should you bring? Assume each of the following: the fuel has an average formula of 15 of the heat generated from combustion goes to heat the water (the rest is lost to the surroundings); the density of the fuel is 0.78 the initial temperature of the water is 25.0 and the standard enthalpy of formation of is -224.4 .

Explanation / Answer

the eqn: C7H16 + 11O2 -----> 7CO2 + 8H2O + heat

dH comb/ mole C7H16 = 44.566 MJ /kg C7H16 = 44.566 kJ/g

dH comb J /ml C7H16 = 44.566kJ/ g * 0.78 g/ml = 34.76 kJ/ml

heat needed, if 100% eff = 36000 g * 4.184 J/gC * 75 C =
11.3 MJ

if 15% eff then heat needed = 100% eff/15% * heat needed if 100% = 75.3 MJ

vol of C7H16 needed = heat needed / (+dH comb / ml C7H16) = 75.3 MJ / 34.76 kJ/ml 2167 ml

liters C7H16 needed = vol ml / 1000ml/liter = 2.17 liters

1 liter = 0.26 US gal; so 2.17 liters * 0.26 gal/liter = 0.56 gal

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