1) Which of the following is true for the sublimation of a solid substance? ? S
ID: 1006408 • Letter: 1
Question
1)
Which of the following is true for the sublimation of a solid substance?
?S = 0 and ?H = 0.
?S > 0 and ?H < 0.
?S < 0 and ?H < 0.
?S > 0 and ?H > 0.
?S < 0 and ?H > 0.
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2)
Calculate the standard entropy change for the following reaction.
2N2(g)
+ 6H2(g)
?
4NH3(g)
191.5
130.6
192.3
794.8 J/K?mol-rxn
–129.8 J/K?mol-rxn
–794.8 J/K?mol-rxn
–737.2 J/K?mol-rxn
737.2 J/K?mol-rxn
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3)
For the reaction given below, ?H0 = ?1516 kJ at 25°C and ?S0 = ?432.8 J/K at 25°C. This reaction is spontaneous ____.
at no temperatures
only below a certain temperature
at all temperatures
only above a certain temperature
cannot tell from the information available
?S = 0 and ?H = 0.
?S > 0 and ?H < 0.
?S < 0 and ?H < 0.
?S > 0 and ?H > 0.
?S < 0 and ?H > 0.
Explanation / Answer
1) S > 0 and H > 0
Sublimation is the process in which solid is converted into gaseous substance directly.
Sublimation: solid +_heat ------> gas
Since energy is absorbed in the sublimation process, enthalpy change is positive and H > 0.
Since entropy of gas is more than that of the solid, entropy change is also positive and S > 0
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