A Closed System of Constant Temperature and Pressure

Let us now consider a closed system approaching equilibrium - this time at constant temperature and pressure - and develop the corresponding equilibrium criteria. For a reversible change in such a system, from the first law (Eq. 12.3.2)  

The conditions, therefore, for equilibrium of a closed system at constant temperature and pressure are  

We apply Eqs 12.3.9 and 12.3.10 to a simple reacting system in the next Example 12.2. We proceed then to develop in Sections 12.4, 12.5, and 12.6, using the same equation, the basis for calculations in the very important for practical applications cases  

N2O4 decomposes according to the reaction N2O4 2NO2. One mole of N2O4 is placed into a piston-and-cylinder arrangement, which is kept at a constant tenq erature of 2S C and a pressure of 1 atm. 

Determine the composition of the mixture at equilibrium by finding the amount of N2O4 consumed when the Gibbs free energy of the system reaches its minimum value. It is given that at 298 K and 1 atm G(N204) = 97.90 G(N02) 52.00, both in kJ/mol. 

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