Equilibrium Conversion by Gibbs Minimization

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Gas-phase catalytic dehydrogenation of 1-Butene gives 1,3-Butadiene by the reaction .


This Demonstration plots the Gibbs free energy (actually, ) versus the reaction coordinate . Here is temperature in kelvin and is the universal gas constant. You can set values of as well as the pressure , expressed in atm. Only low to moderate values of the pressure are allowed. Thus the gas mixture acts as an ideal gas.

To suppress the reverse reaction, steam (acting as an inert gas) is added. You can select a value of the dilution factor (i.e. the number of moles of steam added per mole of 1-Butene).

The equilibrium conversion is achieved when reaches a minimum (indicated by the red dot in the graph).

In accordance with Le Chatelier's principle, you can verify that:

1. The conversion is increased when you increase the temperature. Indeed, this reaction is endothermic (, where is the enthalpy).

2. The forward reaction is favored by low pressures and high dilution factors. Indeed, there are more moles of product than reactant (, where is the stoichiometric coefficient of species ).


Contributed by: Housam Binous, Mohammad Mozahar Hossain, and Ahmed Bellagi (January 2016)
(King Fahd University of Petroleum & Minerals, KSA; ENIM, University of Monastir, Tunisia)
Open content licensed under CC BY-NC-SA




[1] J. R. Elliott and C. T. Lira, Introductory Chemical Engineering Thermodynamics, 2nd ed., Englewood Cliffs, NJ: Prentice Hall International Editions, 2012.

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