Thermodynamics

The following problems are taken from T. L. Brown, H. E. Lemay, B. E. Bursten, & J. R. Burdge, Chemistry: The Central Science, Ninth Edition, Chapter 19.

38)  Calculate ΔS° values for the following reactions. In each case explain the sign of  ΔS°:      

       (a) N₂H₄(g) + H₂(g) 2NH₃(g)

       (b) Al(s) + 3Cl₂(g) 2AlCl₃(s)

       (c) Mg(OH)₂(s) + 2HCl(g) MgCl₂(s) + 2H₂O(l)

       (d) 2CH₄(g) C₂H₆(g) + H₂(g)              

42) A certain reaction has ΔH° = -19.5 kJ and ΔS° = +42.7 J/K.

      (a) Is the reaction exothermic or endothermic?          

      (b) Does the reaction lead to an increase or decrease in the disorder of the system?

      (c) Calculate ΔG° for the reaction at 298 K.

      (d) Is the reaction spontaneous at 298 K?

46) Calculate the change in Gibbs free energy for each of the following reactions. In each case indicate whether the reaction is spontaneous under standard conditions.      

      (a) H₂(g) + Cl₂(g) 2HCl (g)       

      (b) MgCl₂(s) + H₂O(l) MgO(s) + 2HCl(g)

      (c) 2NH₃(g) N₂H₄(g) + H₂(g)

      (d) 2NOCl(g) 2NO(g) + Cl₂(g)

50) From the values given for ΔH° and ΔS°, calculate ΔG° for each of the following reactions at 298 K. If the reaction is not spontaneous under standard conditions at 298 K, at what temperature (if any) would the reaction become spontaneous?  

      (a) 2PbS(s) + 3O₂(g) 2PbO(s) + 2SO₂(g)                ΔH° = -844 kJ, ΔS° = -165 J/K

      (b) 2POCl₃(g) 2PCl₃(g) + O₂(g)                               ΔH° = 572 kJ, ΔS° = 179 J/K

64) Consider the reaction H₂(g) + F₂(g)   2HF(g).

       (a) Calculate ΔG° at 298 K.

       (b) Calculate ΔG at 298 K if the reaction mixture consists of 8.0 atm of H₂, 4.5 atm of F₂, and 0.36 atm of HF.

66) Write the equilibrium-constant expression and calculate the value of the equilibrium constant for each of the following reactions at 298 K.

       (a) NaHCO₃(s) NaOH(s) + CO₂(g)   

       (b) 2HBr(g) + Cl₂(g) 2HCl(g) + Br₂(g)

       (c) 2SO₂(g) + O₂(g) 2SO₃(g)