Answer the following questions related to H2O. Substance ΔG°f at 298K(kJ/mol)
H2O(l) −237.2
H2O(g) −228.4

(a) Using the information in the table above, determine the value of ΔG° at 298K for the process represented by the equation H2O(l)⇄H2O(g).

Question 2
(b) Considering your answer to part (a), indicate whether the process is thermodynamically favorable at 298K. Justify your answer.

Question 3
(c) Considering your answer to part (b), explain why H2O(l) has a measurable equilibrium vapor pressure at 298K.

Question 4
Water vapor can be produced in two different processes, as represented below.

Process 1 Process 2
H2O(s)⇄H2O(g) H2O(l)⇄H2O(g)
(d) In terms of concepts of entropy and the particle-level structure of the different phases of water, explain why the change in entropy, ΔS, is greater for process 1 than for process 2.

1. 8.8kJ/mol

2. The process is not favorable.

3. The reason is in the answer.

4. Process 1.

Explanation:

1. ΔG° = ΔG° products - ΔG° reactants

ΔG° = -228.4kJ/mol - (-237.2kJ/mol) = 8.8kJ/mol

2. The process is not favorable because ΔG > 0

3. As the reaction is an equilibrium, a little amount of water will change from liquid to gas. This is the reason because of water has a measurable equilibrium vapor pressure.

4. Entropy is greater in process 1 because the structure of H2O(s) is more organized than H2O(l) (S of H2O(s) is lower than H2O(l)).

ΔS of H2O(s)⇄H2O(g) is greater than H2O(l)⇄H2O(g)

water and alcohols have similar properties because water molecules contain hydroxyl groups that can form hydrogen bonds with other water molecules and with alcohol molecules, and likewise alcohol molecules can form hydrogen bonds with other alcohol molecules as well as with water.