Hydrogen gas is a very useful reagent with many uses in the petroleum, food, and

Question

Hydrogen gas is a very useful reagent with many uses in the petroleum, food, and chemical industries. Most hydrogen exists in covalently bonded molecules, and atmospheric air contains lass than 1 ppm of diatomic hydrogen. Therefore, hydrogen gas is produced on a large scale for those uses, where steam reforming with methane and electrolysis of water two of the primary methods. The more economic reaction of steam reforming it the reverse of the reaction depicted in Carbon Monoxide and Hydrogen - Sample f in the Simulation. Hydrogen has also bean considered as an alternative fuel tor vehicles designed to combust hydrogen and oxygen, which produces water at a product However, concerns were raised because methane is typically used on a large scale to produce hydrogen gas. Assume that a gallon of gasoline contains 2400 g of carbon. If a gasoline engine achieves 30 miles per gallon, each mile consumes 80 g of carbon (about 107 g of methane contains 80 g of carbon). Alternatively, a hydrogen engine can achieve 80 miles per kilogram of hydrogen gas. What is the mass of methane (CH_4) needed to produce enough hydrogen gas (H_2) to drive one mile using the theoretical hydrogen engine?

Explanation / Answer

Given

with 1 Kg of hydrogen we can drive for 80 miles

for 1 mile we need (1kg/80 miles) = 1000 g / 80 miles = 12.5 g/mile

so we need 12.5 g of H2 for 1 mile

Molar mass of H2 = 2 g/mol

No. of moles of H2 required = Mass / molar mass = 12.5 / 2 = 6.25 moles per mile

steam reforming of methane reaction is

CH4 + H2O CO + 3 H2

so 3 mole of H2 is produced from 1 mole of methane

for 6.25 moles of H2 to be produced we need 6.25 / 3 = 2.083 moles of CH4

Molar mass of CH4 = 16 g/mol

Mass of CH4 = No. of moles * mass = 2.083 moles * 16 g/mol = 33.33 g answer

so we need 33.33 g of methane for 1 mile

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