Kinetics and equilibria for reversible formation of 1:1 monodentate complexes between Pd(H2O)(4)(2+) and acetic, propionic, and glycolic acid (RCOOH) according to the equation Pd(H2O)(4)(2+) + RCOOH reversible arrow Pd(H2O)(3)OOCR(+) + H3O+ (k(1), k(-1)) have been studied as a function of temperature and pressure in an aqueous medium with 0.60 less than or equal to [H+] less than or equal to 1.00 M, [RCOOH]/[H+] less than or equal to 1.0, and ionic strength 1.00 M. Stability constants beta(1) for the formation of acetate, propionate, and glycolate complexes are (2.19 +/- 0.09) x 10(4), (2.10 +/- 0.24) x 10(4), and (6.4 +/- 0.1) x 10(3) M(-1), repectively, at 25 degrees C and for a 1.00 M perchlorate medium. The rate expression, k(obsd) = k(1)[RCOOH] + k(-1)[H+], indicates that reaction between palladium and carboxylate anions is negligible under the experimental conditions used. Values for k(1)/M(-1) s(-1), k(-1)/M(-1) s(-1), Delta H-1 double dagger/kJ mol(-1), Delta H(-1)double dagger/kJ mol(-1), Delta S-1 double dagger/JK(-1) mol(-1), Delta S(-1)double dagger/JK(-1) mol(-1), Delta V-1 double dagger/cm(3) mol(-1), and Delta V(-1)double dagger/cm(3) mol(-1) at 25.0 degrees C are 19.3 +/- 0.6, 32.8 +/- 0.2, 52.5 +/- 0.4, 57.5 +/- 0.4, -44 +/- 1, -23 +/- 1, -8.1 +/- 0.3, and -1.7 +/- 0.2 for acetic acid; 12.0 +/- 1.1, 26.4 +/- 0.3, 55.3 +/- 0.6, 56.8 +/- 0.3, -32 +/- 2, -34 +/- 1, -8.9 +/- 0.8, and -1.7 +/- 0.2 for propionic acid; and 21.1 +/- 0.3, 13.7 +/- 0.1, 53.6 +/- 0.4, 59.2 +/- 0.6, -40 +/- 1, -25 + 2, -3.4 +/- 0.2, and -2.3 +/- 0.2 for glycolic acid. There is no relation between formation rate constants and pK(a) for these carboxylic acids. The nucleophilic properties of the carboxylic acids toward palladium(II) are similar to those of water molecules. A trigonal bipyramidal transition state stabilized by hydrogen bonding between the entering carboxylic acid and the leaving aqua ligand or (equivalent) between the entering oxonium ion and the leaving carboxylate ligand is suggested. Negative entropies, volumes of activation, and volume profiles support a strong contribution from bond making in the activation process.