Homework #7 Oct. 21, 2010 Name Chemistry 331

Transcription

1 Homework #7 Oct. 21, 2010 Name Chemistry 331 Please work all problems. 1. Guanosine triphosphate (GTP), similar to ATP, is an important energy source in biological processes. The equilibrium constant (K) for the hydrolysis of GTP is 1.9x10 5 at 298K. GTP (aq) + H 2 O(l) GDP(aq) + P i (aq) a) Calculate the standard reaction gibbs free energy. G o =. b) If the concentrations of the species are as follows: [GTP] = M [GDP] = 1.0x10-2 M [Pi] = M calculate the free energy change at 298K. G =. c) The sign of G in part a indicates (choose the correct answer) products are more stable reactants are more stable the reaction is at equilibrium the reaction will proceed to make more products the reaction will proceed to make more reactants reactants and products have comparable stabilities

2 d) The sign of G in part b indicates (choose the correct answer) products are more stable reactants and products have comparable stabilities the reaction will proceed to make more reactants the reaction is at equilibrium reactants are more stable the reaction will proceed to make more products 2. Consider the vaporization of some liquid (call it X): X(l) X(g) At 298K, the enthalpy of vaporization of X, H o is kj/mol, and its entropy of vaporization, S o, is J mol -1 K -1. Determine the following for X. a) What is the standard free energy of vaporization of X at 298K? G o =. b) What is the value of the equilibrium constant for the vaporization of X at 298K? K =. [Report to 2 sig figs.] c) What is the vapor pressure of X at 298K? P o =. The pressure of X vapor in a closed container at 298K was found to be 42.4 Torr. What is the value of G for the process X(l) X(g) at the time the pressure was measured? d) G =.

3 e) The answer in part d indicates. Choose one of the following answers: the process is at equilibrium the vaporization process is spontaneous the condensation process is spontaneous f) Compute the vapor pressure if the temperature rises to 313 K? Pressure =. 3. Given the van't Hoff plot, Note: Report numerical answers to 3 significant figures.

4 a) The reaction will favor (products/reactants/neither reactants nor products) upon heating. b) Over the temperature range shown on the graph, the (products/reactants) are more stable under standard conditions. c) Calculate the value of H for this reaction. H =. d) Estimate the temperature at which, under standard conditions, the other side of the reaction becomes favored. T =. [If you answered "reactants" in part b, at what T do products become favored?] e) The value of the equilibrium constant (K) at T=321 K is G =. 4. What is the standard enthalpy of a reaction for which the equilibrium constant is doubled when the temperature is increased by 25 K at 298K? 5. From the data on the website, consider this reaction: VERSION 1 2H 2 (g) + CO (g) CH 3 OH (g)

5 Compute the following, using your data tables at T=298K a) rxnh =. b) rxns =. c) rxng =. Now, compute the same set of variables at T=398K d) rxnh =. e) rxns =. f) rxng =. Recall in the notes, we found this partial differential equation for how G fluctuates with temperature: ( G/ T) p = -S g) As temperature decreases, the free energy (increases/decreases). This equation can be transformed and integrated to give the relationship for the rxng as a function of temperature: G(T 2 )/T 2 = G(T 1 )/T 1 + H(T 1 )[1/T 2-1/T 1 ] h)compute G according to this integrated formula, G =. VERSION 2 For the reaction: 4HCN(g) + 5O 2 (g) 4CO 2 (g) + 2H 2 O(g) + 2N 2 (g) Compute the following, using your data tables at T=298K a) rxnh =. b) rxn S =.

6 c) rxng =. Now, compute the same set of variables at T=444K d) rxnh =. e) rxns =. f) rxn G =. Recall in the notes, we found this partial differential equation for how G fluctuates with temperature: ( G/ T) p = -S g) As temperature decreases, the free energy (increases/decreases). This equation can be transformed and integrated to give the relationship for the rxng as a function of temperature: G(T 2 )/T 2 = G(T 1 )/T 1 + H(T 1 )[1/T 2-1/T 1 ] h)compute G according to this integrated formula, G =. VERSION 3 From the data on the website, consider this reaction: 3NO 2 (g) + H 2 O (l) 2HNO 3 (aq) + NO (g) Compute the following, using your data tables at T=298K a) rxnh =.

7 b) rxns =. c) rxng =. Now, compute the same set of variables at T=444K d) rxnh =. e) rxns =. f) rxn G =. Recall in the notes, we found this partial differential equation for how G fluctuates with temperature: ( G/ T) p = -S g) As temperature decreases, the free energy (increases/decreases)this equation can be transformed and integrated to give the relationship for the rxng as a function of temperature: G(T 2 )/T 2 = G(T 1 )/T 1 + H(T 1 )[1/T 2-1/T 1 ] h)compute G according to this integrated formula, G =. VERSION 4 From the data on the website, consider this reaction: 3H 2 (g) + HCN(g) CH 4 (g) + NH 3 (g) Compute the following, using your data tables at T=298K a) rxnh =. b) rxns =.

8 c) rxng =. Now, compute the same set of variables at T=402K d) rxnh =. e) rxns =. f) rxn G =. Recall in the notes, we found this partial differential equation for how G fluctuates with temperature: ( G/ T) p = -S g) As temperature increases, the free energy (increases/decreases) This equation can be transformed and integrated to give the relationship for the rxng as a function of temperature: G(T 2 )/T 2 = G(T 1 )/T 1 + H(T 1 )[1/T 2-1/T 1 ] h)compute G according to this integrated formula, G =.