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 38 L 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 25.0 C; and the standard enthalpy of formation of C7H16 is -224.4 kJ/mol. Express your answer using two significant figures.

Explanation / Answer

heat required to boil 38 g water [density of water = 1 g/ml, so volume = mass]

q = mCpdT = 38 x 4.184 x (100-25) = 11.924 kJ

deltaH energy released per mole burning of C7H14 = 224.24 kJ/mol

15% = 224.24 x 15/100 = 33.66 kJ/mol

Calculate moles of C7H16 required to release 11.924 kJ of heat = 1 x 11.924/33.66 = 0.3542 mols

mass of fueal required = 0.3542 x 100.21 = 35.49 g

Volume of fuel required = 35.49/0.78 = 45.5 ml

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