Free Energy in Industry

Many, many products in industry are made by reactant-favored reactions. Each of these reactions must be coupled to a product-favored reaction in order to be useful. Most of these reactions fall into one of two classes:

1. Purifying metals or other elements from their ores. Metals are usually found in one of their oxidized states in their ores. These metals must be reduced in reactant-favored processes in order to be purified.

2Fe2O3(s)			4Fe(s) +	3O2(g)	DGº = 742.2 kJ
2NaCl(s)			2Na(s) +	Cl2(g)	DGº = 384.138 kJ
HgS(s) +	O2(g)		Hg() +	SO2(g)	DGº = -249.594 kJ

2. Raw materials for other products. The most important raw material in the plastics industry is the alkene ethene (ethylene). It is produced in a reactant-favored reaction from ethane:

C₂H₆(g) H₂(g) + C₂H₄(g)     DGº = 100.97 kJ

Sodium hydroxide and chlorine gas, both used in many industrial processes including the production of paper, are produced from a simple sodium chloride solution:

2NaCl (aq) + 2H₂O() 2NaOH(aq) + Cl₂(g) + H₂(g)     DGº = 422.22 kJ

Most of these reactions are made product-favored by heat or electricity. Where does the energy used to drive these reactions come from? Both the heat and electricity usually come from the burning of fossil fuels, e.g. coal:

C(s) + O₂(g) CO₂(g)     DGº = -394.359 kJ

methane (natural gas):

CH₄(g) + 2O₂(g) CO₂(g) + 2H₂O(g)     DGº = -800.78 kJ

or oil:

C₁₇H₃₆(l) + 26O₂(g) 17CO₂(g) + 18H₂O(g)     DGº < -20,000 kJ

Calculate the heat released by burning 1.00 kg of coal.

Is this heat sufficient to reduce 1.00 kg of iron(III) oxide to iron metal?

-32800 kJ • 2 mol Fe₂O₃/742.2 kJ • 159.7 g/1 mol • 1 kg/1000 g = 14.1 kg

Free Energy in Industry