20. Predict the sign of S of the system for each of the following reactions. (1)
ID: 878977 • Letter: 2
Question
20. Predict the sign of S of the system for each of the following reactions.
(1) 2A(s) + B2(g) 2AB(g)
(2) X4Y10(g) X4Y10(l)
A. S is zero for both reactions.
B. S is negative for both reactions.
C. S is positive for both reactions.
D. S is negative for (1) and positive for (2).
E. S is positive for (1) and negative for (2).
21. According to the second law of thermodynamics, all reactions proceed spontaneously in the direction that increase
A. The entropy of the system
B. The free energy of the system
C. The entropy of the surroundings
D. The free energy of the surroundings
E. The entropy of the universe
22. For a reaction to be at equilibrium, it is necessary that
(1) Ssys = 0 (2) Ssys = –Ssurr (3) Gsys = 0
A. (1) B. (3) C. (1) and (3) D. (2), and (3) E. (1), (2), and (3)
23. The signs of G, H, and S at 25°C are shown below for three reactions. Which reaction(s) could proceed in the reverse direction if the temperature was sufficiently increased?
reaction
G
H
S
(1)
–
+
+
(2)
–
–
+
(3)
–
–
–
A. (1) B. (2) C. (3) D. (1), and (3) E. None of these
24. A reaction, A(g) B(g) has a H° = 61.9 kJ/mol and S° 405.4 J/K. Which choice best describes what occurs when a 1.0-L vessel is filled with 1 atm of each gas?
A. The reaction proceeds in the forward direction regardless of temperature.
B. The reaction proceeds in the reverse direction regardless of temperature.
C. The reaction proceeds in the forward direction at T > 153 K.
D. The reaction proceeds in the reverse direction at T > 153 K.
E. The reaction is at equilibrium at T > 153 K.
reaction
G
H
S
(1)
–
+
+
(2)
–
–
+
(3)
–
–
–
Explanation / Answer
20) answer : E) S is positive for (1) and negative for (2).
explanation:
S is positive at given conditions
1) more gas moles are produced than reacted.
2) a solid turns into a liquid or gas
3) a liquid turns into a gas
21) answer : E). The entropy of the universe
explanation:
According to the second law of thermodynamics, all reactions proceed spontaneously in the direction that increase in the entropy of the system and surroundings.
spontenous when Suniv > 0
22) answer : D) (2), and (3)
explanation:
Suniv = 0 & Gsys = 0. in the both conditions the reaction is at equilibrium.
Suniv = 0 = Ssys + Ssurr
Ssys = - Ssurr
23) answer : C. (3)
explnation: G > 0 reaction can spontaneously proceed to the left
24 ) answer : C) The reaction proceeds in the forward direction at T > 153 K.
G < H - T S
0 < 61.9 - T (0.405)
153 < T
T > 153 K
G < 0 reaction can spontaneously proceed to the forward
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