Consider the following compounds and their standard free energies of formation: Which of these liquids is (are)thermodynamically unstable?
A)2
B)1,3,and 5
C)1 and 4
D)2 and 3
E)2 and 4

Question

Consider the following compounds and their standard free energies of formation:  Which of these liquids is (are)thermodynamically unstable?
A)2 
B)1,3,and 5 
C)1 and 4 
D)2 and 3 
E)2 and 4

Quizplus · Accepted Answer

To determine thermodynamic stability, we can compare the standard free energy of formation of the liquid with that of its constituent elements. If the free energy of the liquid is greater than the sum of the free energies of the elements, the liquid is unstable and will tend to decompose. 
1) Ethanol: (-174.8) = -68.15 + (-249.7): Stable 
2) Acetone: (-177.7) > -94.76 + (-230.3): Unstable 
3) Benzene: (124.4) = 0 + 82.9: Stable 
4) Toluene: (50.4) > 0 + 82.9: Unstable 
5) Cyclohexene: (-4.92) > 0 + 62.4: Unstable 
Therefore, choices 1, 3, and 5 are stable, while choices 2 and 4 are unstable. So, option (B) is correct.

Consider the Following Compounds and Their Standard Free Energies of Formation