On a 5 day wilderness expedition you'll need to heat 4.0 kg of water to the boiling point each day. The air temperature will average 25°C.

Question

You have available canisters of compressed butane C4H10 fuel, which you'll burn to heat the water. Each canister has 100.g of butane in it. What is the minimum number of fuel canisters you must bring? The standard heat of formation of butane at 25°C is −125.7/kJmol.

Canisters = ______

Answer 1

4.0 kg H2O / day x 5 days = 20 kg H2O

heat needed to boil 20 kg of water starting @25º = q = mC∆T

q = (20 kg)(4.184 kJ/kgº)75º) = 6276 kJ needed

molar mass butane = 58.1 g mole

100 g butane / container x 1 mole / 58.1 g = 1.72 moles butane / container

1.72 mol butane / container x 125.7 kJ / mol = 216 kJ / container

6276 kJ x 1 container / 216 kJ = 29 containers needed = 30 containers minimum (due to rounding errors)