Module 5: Electrochemistry
Lecture 21 : Review Of Thermodynamics
 
21.6)
One mole of an ideal gas is compressed from 1 atm to 100 atm at 350 K. What are the changes in the Gibbs free energy and the Helmholtz free energy?
     
21.7)
At constant pressure dG = -SdT, and (G/ T)P = -S. Using the relation G = H -TS or S = (H-G)/T show that (G/T)/ T = -H/T 2. This is called the Gibbs-Helmholtz equation. Applying this to changes in free energies in reactions, we get [( G/T)/ T]P = - H / T2.
   
21.8) If Hof is independent of T, the above equation can be integrated to give G2 / T2 - G 1 / T1 = H(1/T2 – 1/T 1 ). The same formula can be applied for Go as well . For the reaction N2 + 3H2 2NH3 at 298 K, Go = Gof = -3.97 kcal/mol. Calculate Keq using Go = -RT ln Keq .If H o f = -11.04 kcal/mol for NH3, and it is independent of temperature, calculate Keq at 500 K.
   
21.9)


In a gas phase reaction A + 2B 3C + 4D, 2 moles of A, 1 mol of B and 2 moles of D were mixed at 298K. When equilibrium was reached, the total pressure was 1 bar and the amount of C present was 0.3 moles. Calculate the equilibrium constant and the value of Go. First calculate the number of moles of all species at equilibrium.
 
21.10)

Starting with dH = ( H/ T)P dT + ( H/ P)T dp, show that (H/ P)T = - CP
where = (T/ P)H. is the Joule Thompson coefficient. When > 0, gases cool on expansion. This principle is used in refrigeration.

   
21.11)

Two containers A and B are placed next to each other. Both contain ideal gases at temperature T. The container A has volume VA and nA moles of A and container B has a volume VB and nB moles of B. When the partition between A and B is removed, both the gases mix and the entropy increases. Show that the entropy of mixing is - (nA + nB) [xA ln xA + xB ln xB], where xA and xB are the mole fractions of A and B in the mixture.

   
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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