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 30L of water for your group. What volume of fuel should you bring? Assume each of the following: the fuel has an average formula of C7H16; 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 g/mL; the initial temperature of the water is 25.0C and the standard enthalpy of formation of C7H16 is -224.4 kj/mol.

Explanation / Answer

C7H16 + O2 ====> 7CO2 (g)+ 8H2O (g)

Molar mass of C7H16 is 12*7 + 16*1.008 = 100.2 g/mole

H = 8(241.8) + 7(-393.5) - (-224.4)

H = -4464.5 kJ

q required = 30,000g * 75c * (4.184joules/gC) /( 0.15 efficiency) /(1000J/kJ) = 62,760 kJ

62760kJ/4464.4kJ/mole * 100.2g/mole / 0.78g/mL = 1805.9 mL= 1800 mL (*2 sig figs)

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