Consider two carboxylic acids (acids that contain the -COOH group): CH3COOH (acetic acid, Ka = 1.8 × 10-5) and CH2ClCOOH (chloroacetic acid, Ka = 1.4 × 10 -3). (a) Calculate ×G° for the ionization of these acids at 25°C. (b) From the equation ×G° 5 ˆ†H° 2 Tˆ†S°, we see that the contributions to the ˆ†G° term are an enthalpy term (ˆ†H°) and a temperature times entropy term (Tˆ†S°). These contributions are listed below for the two acids:

Which is the dominant term in determining the value of ˆ†G° (and hence Ka of the acid)? (c) What processes contribute to ˆ†H°? (Consider the ionization of the acids as a Bronsted acid-base reaction.) (d) Explain why the TDS° term is more negative for CH3COOH.

Transcribed Image Text:

A19 kJ/mol) -0.57 -4.7 TAS°1«J/mol) CH,COOH CH CICOOH 27.6 21.1