Consider a reaction where S rxn = -315 J/K and H rxn = -45.6 kJ. Which statement
ID: 956482 • Letter: C
Question
Consider a reaction where S rxn = -315 J/K and H rxn = -45.6 kJ. Which statement is true about the spontaneity of this reaction?
A) This reaction is nonspontaneous at 25°C but will become spontaneous if the temperature is decreased to -130°C. B) This reaction is spontaneous at 25°C, but will become nonspontaneous if the temperature is decreased to -130°C. C) Decreasing the temperature will have no effect on the spontaneity of the reaction. It is nonspontaneous at 25°C and will become even less spontaneous as the temperature decreases. D) This reaction is nonspontaneous at 25°C but will become spontaneous if the temperature is increased to 145°C.Explanation / Answer
G = H-TS = -45600 - T*-315
A)
at 25C = 298K --> G = -45600 + 298*315 = 48270; this is non-spontanous
further analysis,
note that
H < TS
H/S < T
(-45600/-315 < T
T > 144.7 K = -128.8 C (in order to be spontanous)
therefore; OPTION B
must be true
This reaction is spontaneous at 25°C, but will become nonspontaneous if the temperature is decreased to -130°C.