Consider acetic acid, CH3COOH, The active ingredient in vinegar. It is also responsible for the sour taste of wine when gets exposed to air. Bacterial oxidation turns alcohol to acid.
C2H5OH (aq) +O2 → CH3COOH (aq) +H2O
The following data may be useful:
C2H5OH (aq): ∆H˚f = -288.3 kJ/mol
S˚= 145.5 J/mol.k
CH3COOH (aq): ∆H˚f = -485.8 kJ/mol
S˚= 178.7 J/mol.k
(a)Calculate ∆H˚ and ∆ S˚ 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 ∆ S˚ 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 ∆G at 25˚C for the formation of acetic acid from ethanol (see raction above)when (CH3COOH)=0.200M,PO2=1.13 atm , and (C2H5OH)=0.125M.
(f)Calculate ∆G˚ for the ionization of acetic at 25˚C (Ka = 1.8*10^-5)
This solution explains:
1) How to calculate entropy and enthalpy for the conversion of wine to vinegar.
2) How to determine if this reaction is spontaneous at 25 C and at 4 C.
3) How to calculate the entropy of a change from a liquid to a gas.
4) How to calculate standard molar entropy.
5) How to calculate Gibbs free energy.
6) How to calculate Gibbs free energy based on an ionization constant.