Introduction and Perfect Gas Equilibria

The starting point to calculate the equilibrium state of a chemical reaction is the Clausius inequality, introduced in Section 3.1.3 for physical transformations of pure 

For illustration, we consider a vessel where a chemical reaction takes place (the system), which is surrounded by a reservoir of a cooling (heating) medium (the surrounding). The vessel and the reservoir form a closed isolated system. We assume that both have the same temperature after the reaction has taken place, and that the generated (or consumed) heat Qreaction is reversibly transferred from the vessel to the reservoir or vice versa. Thus we have  

If we use the common convention that Qreaction is negative, if energy has left the vessel (exothermic reaction), it follows that the change of the entropy of the 

Josiah Willard Cibbs (1839-1903), an American mathematical physicist, contributed much to the foundation of chemical thermodynamics. He was the first in the USA to receive a PhD in engineering (Yale, 1863), and one of the earliest theoretical physicists in America and probably one of the earliest theoretical chemists. Cibbs can also be regarded as the Inventor of vector analysis. 

For an exothermic reaction, the entropy of the system decreases (Qreaction 0). and the entropy of the surrounding increases by the same amount. 

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