Given the following reaction: 4H2O(g) + 3Fe(s)  Fe3O4(s) + 4H2(g)

Question

How much iron( in grams) is need to produce enough hydrogen gas to fill a 17.8 L tank at 34.0oC and

815 torr?

Answer 1

First let’s calculate how many moles of H2 produced. We use the ideal gas equation:

PV = n RT where P = 815/760 = 1.072 atmospheres, V = 17.8 L, T = 307°K, and R = 0.0821 L-atm/mol-deg . Solve for n to get 0.757 moles H2.

Next we need the conversion factor of the relation of moles of H2 to moles of Fe.

This factor is 3 moles Fe / 4 moles H2= 0.75 moles Fe per mole of H2.

Multiply 0.75 x the number of H2 moles determined above to get 0.75 x 0.757 = 0.568 moles Fe.

Convert 0.568 moles Fe to grams Fe by 0.568 moles Fe x atomic mass Fe / mole

= 0.568 moles Fe x 55.845 g Fe /mole = 31.7 g Fe needed.