Gases - Fundamentals of Industrial Chemistry: Pharmaceuticals, Polymers, and Business - page 19

2( − 110.5 kJ) − 2( − 74.8 kJ) = − 71.4 kJ

2 CH 4(g) + O 2(g) 2 CO (g) + 4 H 2(g) Δ H ° = − 71.4 kJ

A second reaction for the oxidation of methane is steam reforming.

CH 4(g) + H 2 O (g) CO (g) + 3 H 2(g)

H ∘ f =− 241.8 kJ/mol. For this reaction, we can calculate the

standard enthalpy change to be

For H 2 O (g) , Δ

(( − 110.5 kJ)) − (( − 74.8 kJ) + ( − 241.8 kJ)) = 206.1 kJ

CH 4(g) + H 2 O (g) CO (g) + 3 H 2(g)

Δ H ° = 206.1 kJ

This reaction is highly endothermic. By varying the amount of oxygen
and water, the two reactions can be done together in a manner so that the
heat flow is controlled. The enthalpy calculations are not as simple as shown
here because the reactions are not done at standard conditions and enthalpy
changes with pressure and temperature. High pressures and temperatures of
about 1200 ∘ C are common. For precision, it needs to be calculated or exper-
imentally determined for the conditions of interest.
For steam reforming, the carbon monoxide can in turn be oxidized by reac-
tion with water to form carbon dioxide and hydrogen.

CO (g) + H 2 O (g) CO 2(g) + H 2(g)

H ∘ f =− 393.5 kJ/mol. For this reaction, we can calculate the

standard enthalpy change to be

For CO 2(g) , Δ

( − 393.5 kJ) − ( − 110.5 + ( − 241.8 kJ)) = − 41.2 kJ

CO (g) + H 2 O (g) CO 2(g) + H 2(g) Δ H ° = − 41.2 kJ

When the two steam reforming reactions are combined, the overall reaction
converts one mole of methane to 4 moles of hydrogen.

CO 2(g) + 4 H 2(g)

CH 4(g) + 2 H 2 O (g)

Most hydrogen made in the United States is made by this steam reforming
process. One mole of methane can be converted to 4 moles of hydrogen.
Taking into account molecular weights, 16 g of methane is converted to 8 g