EXERCISES #7
Name
Assignment date: 16 December 04 Hand back before: 7th January 05 (midday) Discussion: 8th January 05
1.   Calculate the equilibrium constant of the reaction 2 H2S (g) + S02 (g) 5 2 H20 (g) + 3 S (s) at 25 °C,
Compound                H20 (g)	H2S (g)        S02 (g)
AjG° (298 K; kJ mol"1) -228,59	-33,60 -300,19
	[AT°= 5,39.1015]
The standard enthalpy of the reaction N2 (g) + 3H2(g)52 NH3 (g) at 25 °C equals molar entropies of individual compounds are following:	-92,4 kJ/mol. Standard
Compound                N2 (g)	H2 (g)         NH3 (g)
5° (298 K; J mol"1 K"1) 191,58	130,67 192,59
Calculate the equilibrium constant of the reaction at 25 °C.	[K°= 6,67.105]
Estimate the temperature at which CuS04.5 H20 undergoes dehydration.	
Compound           H20 (g)         CuS04 (s)	CuS04.5H20 (s)
S,„° (J mol"1 K'1)         188,83 109,0	300,4
4//°(kJinor')         -241,82 -771,36	-2279,7
[T = 397,5 K]	
4. The dissociation vapor pressure of NH4C1 at 427 °C is 608 kPa but at 459 °C it has risen to 1115 kPa. Calculate (a) the equilibrium constant, (b) the standard reaction Gibbs energy, (c) the standard enthalpy, (d) the standard entropy of dissociation, all at 427 °C. Assume that the vapor behaves as a perfect gas and that AS° and AH° are independent of temperature in the range given.
[a) K° = 9,24; b)ArG°= -12,94 kJ moľ'; c)ArH°= 161,49 kJ moľ1; d) A,S° = 249,18 J IC'mol"';]
5. Estimate S° and AjH° of 4-chloro-cyclohexanenitrile using Benson thermochemical tables.
[AjH°= -8.72 kcal moľ'; S° = 93.9 cal K"' moľ';
6. Calculate the pH of (a) 0,10 M NaHC02 (aq), (b) 0,20 M C6H5COONa, (c) 0,150 M HCN (aq). pKa (HCOOH) = 3,75; pKa (PhCOOH) = 4,19; pKa (HCN) = 9,31.
[a) 8,38; b) 8,75; c) 5,07]
Es gibt die erstaunliche Möglichkeit, dass man einen Gegenstand mathematisch beherrschen kann, ohne den Witz der Sache wirklich erfasst zu haben.
Albert Einstein
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