1. Below what temperature does the following reaction become nonspontaneous? 2 H
ID: 911223 • Letter: 1
Question
1. Below what temperature does the following reaction become nonspontaneous? 2 HNO3(aq) + NO(g) ? 3 NO2(g) + H2O(l) ?H = +136.5 kJ; ?S = +287.5 J/K
(A) 39.2 K (B) 151 K (C) 475 K (D) This reaction is nonspontaneous at all temperatures. (E) This reaction is spontaneous at all temperature
2.Consider the following reaction at constant P. Use the information here to determine the value of ?Ssurr at 355 K. Predict the spontaneity of the reaction at this temperature. 2 NO(g) + O2(g) ? 2 NO2(g) ?H = -114 kJ
(A) ?Ssurr = +114 kJ/K, reaction is spontaneous (B) ?Ssurr = +114 kJ/K, reaction is not spontaneous (C) ?Ssurr = +321 J/K, reaction is spontaneous (D) ?Ssurr = -321 J/K, reaction is not spontaneous (E) ?Ssurr = +321 J/K, it is not possible to predict the spontaneity of this reaction without more information.
3.Predict the sign of ?S in the system for each of the following processes:
(a). CO2(s) ? CO2(g) (sublimation of dry ice) (b). CaSO4(s) ? CaO(s) + SO3(g) (c). N2(g) + 3 H2(g) ? 2 NH3(g) (d). I2(s) ? I2(aq)(dissolution of iodine in water
Explanation / Answer
1)
?G = ?H - T?S
At Equilibrium, ?G = 0
0 = ?H - T?S
?H = T?S
Here. ?H = +136.5 kJ or +136500 J and ?S = +287.5 J/K
T = ?H/?S = 136500 J / 287.5 J/K
T = 474.78 K or 475 K
Hence the correct answer is C) 475 K
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