Problems
5.1 At equilibrium, what can be said about the Gibbs energy?
5.2 For a spontaneous process at constant pressure, will the change in Gibbs energy be positive,
negative, or zero?
5.3 For a process with two components, what can be said about the Gibbs energy when the
mole fractions are equal?
5.4 If the equilibrium constant is strongly temperature-dependent, what can be said about the
relative entropic and enthalpic contributions to the Gibbs energy?
5.5 If the equilibrium constant is independent of temperature, what can be said about the
relative entropic and enthalpic contributions to the Gibbs energy?
5.6 In the reaction CH 3 COO−+H 2 O ↔CH 3 COOH +OH−state whether each species is acting
as a base, acid, neither, or both.
5.7 Calculate the pH for a solution with an H 3 O+molar concentration of (a) 10−^5 M and (b) 10−^9 M.
5.8 The equilibrium constant for a particular electrochemical reaction is 0.5. Is the standard-
reaction Gibbs energy greater than zero, less than zero, zero, or undetermined?
5.9 At equilibrium, for the reaction A ↔B, the final concentration of A is twice that of B.
What can be said about the Gibbs energy for this reaction at equilibrium?
5.10 After 100 mL of 0.1 M NaOH is added to 900 mL of a solution containing 0.03 mol of acetic
acid (CH 3 COOH, pKA=4.75) and 0.02 mol of NaCl, what is the pH of the final solution?
5.11 Acetic acid is a weak acid with a pKAof 4.75. What is the pH of a solution prepared by
adding 0.1 mol of acetic acid and 0.03 mol of NaOH to water at a final volume of 1 L?
5.12 After adding 0.01 M HCl to distilled water that is initially at pH 7, what is the final pH?
5.13 An isoelectric pH is the pH at which the molecule has no net average charge. What is the
isoelectric pH of glycine?
5.14 A 25-mL solution has a strong base at 0.15 M. What is the initial pH?
5.15 The buffer Tris, or tris(hydroxymethyl)aminomethane, has a pKAof 8.3. At what pH would
this buffer have equal molar concentrations of Tris and its conjugate base?
5.16 Why is electron transfer often coupled to proton transfer?
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