Page 259 - Thermodynamics of Biochemical Reactions

Chapter 3 Chemical Equilibrium in One Phase Systems

3.1 Use the table of basic data to calculate the acid dissociation constants of ATP, ADP, and Pi and the equilibrium constant
for the reference reaction ATP4- + H20 = ADP3- + HPO4'-+ H+ at 298.15 K and ionic strengths of 0, 05, 0.10, 0.15, 0.20,
and 0.25 M.

3.2 For the solution reaction A = B, assume that the standard Gibbs energy of formation of A is 20 kJ mol-' and of B is 18
kJ mol-' at 298.15 K. (a) For a reaction starting with a mole of A at a concentration of 1 M, plot the Gibbs energy of the
mixture versus extent of reaction from zero to unity and identify the approximate extent of reaction at equilibrium. (b)
Identify the equilibrium extent of reaction more precisely by plotting the derivative of the Gibbs energy of the mixture with
respect to extent of reaction. (c) Calculate the equilibrium constant and verify the equilibrium extent of reaction.

3.3 Calculate the standard Gibbs energy changes and equilibrium constants in terms of species for the following reactions at
298.15 K and ionic strengths of 0, 0.10, and 0.25 M. Summarize the calculations in two tables.
(a) NAD- + H2(g) = NADH2- + Hf
(b) NADP3- + Hz(g) = NADPH4- + H+
(c) NAD- + NADPH4-= NADH2- + NADP3-
(d) CH3 CHIOH + NAD- = CH3 CHO + NADH2- + H+
(e) CH3 CHO + NAD- + H20 = CH3 C02- + NADH'- + 2 H+
(0 C3 H7 NO2 + NAD- + H20 = C3 H3 0-+ NADH2- + N&+ + H+
The last reaction involves L-alanine and pyruvate.

3.4 Plot the acid dissociation constant of acetic acid from 0 OC to 50 "C given that at 298.15 K, Af Co = 27.14 kJ mol-',
A, H" = -0.39 kJ mol-', and A, C,"= -155 J K-' mol-". Assume zero ionic strength.

3.5 (a) Calculate the function of T that gives the values of the Debye-Huckel constant a at the temperatures in Table 3.1 in
Section 3.7. Plot the data and the function. (b) Calculate the function of T for RTa. (c) Calculate the function of T for
RT2(da/aT)p. (d) Use these functions to calculate these coefficients at 0, 10,20,25, 30, and 40 OC.

3.6 Calculate the standard Gibbs energies of formation of the three species of ATP at temperatures of 283.15 K, 298.15 K,
298.15 K and ionic strengths of 0,O. 10, and 0.25 M.

3.7 Calculate the adjustments to be subtracted from pH, obtained with a pH meter to obtain pH,= -log[H+ at 0 "C to 40 "C
and ionic strengths of 0, 0.10, and 0.25 M.

3.8 Calculate the standard enthalpies of formation of the three species of ATP at 283.15 K, 298.15 K, and 313.15 K at ionic
strengths of 0, 0.10, and 0.25 M

3.9 There are two ways to obtain values for the enthalpy coefficient in equation 3.6-5 as a function of temperature: (a)
Calculate the derivative with respect to T of the Gibbs energy coefficient divided by T. (b) Fit the enthalpy coefficients of
Clarke and Glew to AT2+ BT3. Use both of these methods and make plots to compare these functions with the values in
Table 3.1

3.10 Plot the activity coefficients of ions with charges I, 2, 3, and 4 versus the ionic strength at 0 "C. Repeat these calcula-
tions at 25 "C and 40 "C