Help with chemistry textbook problem please? The solutions are provided, but I don’t know the steps.

Question

Consider acetic acid, CH3COOH, the active ingredient in vinegar. It is also responsible for the sour taste of wine when wine gets exposed to air. Bacterial oxidation turns alcohol to acid.

C2H5OH(aq) + O2(g) —> CH3COOH(aq) + H2O(l)

The following data may be useful:

C2H5OH(aq): ΔHf° = -288.3 kJ/mol; S° = 148.5 J/mol•K

CH3COOH(aq): ΔHf° = -485.8 kJ/mol; S° = 178.7 J/mol•K



(a) Calculate ΔH° and ΔS° for this process.

(b) Is the reaction spontaneous at 25°C? At 4°C?

(c) The heat of vaporization for acetic acid is 24.3 kJ/mol. Its normal boiling point is 118.5°C. Calculate ΔS° for the reaction: CH3COOH(l) —> CH3COOH(g)

(d) What is the standard molar entropy for CH3COOH(g), taking S° for CH3COOH(l) to be 159.8 J/mol•K

(e) Calculate ΔG at 25°C for the formation of acetic acid from ethanol (see reaction above) when [CH3COOH] = 0.200 M, PO2 = 1.13 atm, and [C2H5OH] = 0.125 M.

(f) Calculate ΔG° for the ionization of acetic acid at 25°C (Ka = 1.8 x 10-5).

The above question set is a summary problem from my textbook. The solutions listed are:

(a) ΔH°= -483.3 kJ; ΔS°= -104.9 J/K

(b) ΔG° (at 25°C)= -452.0 kJ; yes

ΔG° (at 4°C)= -454.2 kJ; yes

(c) 62.1 J/K

(d) 221.9 J/mol•K

(e) -451.1 kJ

(f) 27.1 kJ

The solutions were provided, but I don’t know the steps to solve the problems. If someone could help me walk through this problem, that’d be great. Thanks!

Answer 1

a) The ∆Hºrxn = ∑∆Hºf products - ∑∆Hºf products. For the current reaction, we need to know the ∆Hºf for H2O(l) since it is a product. Looking it up, I find it to be -285.8kJ/mol. Solving for ∆Hºrxn we have...

(-485.8 + -285.5) - (-283.3 + 0) = -483.3 kJ = ∆H

Doing the same for ∆Sº after looking up values for H20(l) and O2(g) we have...

(178.7 + 69.9) - (148.5 + 205) = -104.9 J/K = ∆S

b) If ∆Gº is negative, it is spontaneous

∆Gº = ∆Hº - T∆Sº = 483.3 kJ = 298K(-0.1049 kJ/K) = -452.0 kJ YES it is spontaneous

Sorry, I've run out of time for now. Hopefully someone else will finish. If not, perhaps I can return at a later time and finish up. I think it unfair for them not to provide all the necessary data, however.