Consider the following reaction and its corresponding thermodynamic data to answ
ID: 1006268 • Letter: C
Question
Consider the following reaction and its corresponding thermodynamic data to answer the next two questions:
2 H2S(g) + 3 O2(g) 2 SO2(g) + 2 H2O (g) H = -1036 kJ/mol; S = -153.2 J/mol•K
What is the Gibbs Free-Energy change, G for this reaction at 25 oC?
a) G = 44618 kJ/mol
b) G = 2794 kJ/mol
c) G = -990 kJ/mol
d) G = -1082 kJ/mol
e) G = -46690 kJ/mol
8. Given the signs of H and S above, what can be stated about the spontaneity of this chemical reaction?
a) This reaction is spontaneous under all temperatures.
b) This reaction is non-spontaneous under all temperatures.
c) This reaction is spontaneous above the temperature 148 K and non-spontaneous below 148 K.
d) This reaction is spontaneous below the temperature of 6762 K and non-spontaneous above 6762.
e) This reaction is spontaneous above the temperature of 6762 K and non-spontaneous below 6762 K.
The answes are C & D. Please explain how.
Explanation / Answer
T = 25 oC = (25+273) K = 298 K
H = -1036 KJ/mol
S = -0.1532 KJ/molK
G = H - T*S
= -1036 - 298*(-0.1532)
= -990 KJ/mol
Answer: c
8)
G = H - T*S
The reaction is spontaneous when G is negative
G <0
H - T*S <0
-1036 - T*(-0.1532) < 0
T< 6762 K
Answer: D