Ch 16 QUIZ - AP Chemistry

Name:_______________________________ Date:_________________ Hr:____
AP CHEMISTRY
Ch 16 – Spontaneity, Entropy, and Free Energy
SPONTANEITY, ENTROPY, AND FREE ENERGY
TOTAL: /48
You may use your chemistry textbook, class notes, handouts, labs, or any other notes you
make. You may collaborate with any other student currently enrolled in AP Chemistry at GHS.
You may not use any adults, the internet, or other electronic resources. You may choose not to
collaborate with another student (please respect the decision of those who choose to work on
their own). Show all work with appropriate significant figures for full credit.
Multiple Choice (10 points – 2 points each)
Identify the letter of the choice that best completes the statement or answers the question.
Mathematical set-ups and/or verbal reasoning must be given for each question, which might
include why other choices may not be correct. Attach a sheet of paper if needed. No credit
will be awarded for only recording the letter of the answer.
QUIZ
_____ 1. Thermodynamics can be used to determine all of the following EXCEPT
(A) the direction in which a reaction is spontaneous.
(B) the extent to which a reaction occurs.
(C) the rate of reaction.
(D) the temperature at which a reaction is spontaneous.
(E) the enthalpy change of a reaction.
_____ 2. Predict the signs of ∆H, ∆S, and ∆G for the combustion of hydrogen gas at 25 °C.
2 H 2 (g) + O 2 (g) 2 H 2 O(l)
(A) ∆H < 0, ∆S < 0, ∆G < 0
(B) ∆H < 0, ∆S > 0, ∆G < 0
(C) ∆H > 0, ∆S < 0, ∆G < 0
(D) ∆H > 0, ∆S > 0, ∆G < 0
(E) ∆H > 0, ∆S < 0, ∆G > 0
_____ 3. Which reaction is likely to have a negative change in entropy
(A) 2 NH 3 (g) N 2 (g) + 3 H 2 (g)
(B) CaO(s) + CO 2 (g) CaCO 3 (s)
(C) NaCl(s) Na + (aq) + Cl - (aq)
(D) N 2 O 4 (g) 2 NO 2 (g)
(E) 2 C(s) + O 2 (g) 2 CO(g)
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Name:_______________________________ Date:_________________ Hr:____
AP CHEMISTRY
Ch 16 – Spontaneity, Entropy, and Free Energy
QUIZ
_____ 4. Diluting concentrated sulfuric acid with water can be dangerous because the
temperature of the solution can increase rapidly. What are the signs of ∆H, ∆S, and ∆G for this
process
(A) ∆H < 0, ∆S < 0, ∆G < 0
(B) ∆H > 0, ∆S < 0, ∆G < 0
(C) ∆H < 0, ∆S > 0, ∆G < 0
(D) ∆H > 0, ∆S > 0, ∆G < 0
(E) ∆H > 0, ∆S < 0, ∆G > 0
_____ 5. For a chemical system, ∆G° and ∆G are equal when
(A) the equilibrium constant, K, equals 1.
(B) the equilibrium constant, K, equals 0.
(C) the system is at equilibrium.
(D) The reactants and products are in the gas phase.
(E) the reactants and products are in their standard states.
QUIZ IS CONTINUED ON THE NEXT PAGE
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Name:_______________________________ Date:_________________ Hr:____
AP CHEMISTRY
Ch 16 – Spontaneity, Entropy, and Free Energy
QUIZ
Free Response (38 points)
Show all work with appropriate significant figures for full credit.
6. (8 points) Cells use the hydrolysis of adenosine triphosphate, abbreviated as ATP, as a
source of energy. Symbolically, this reaction can be written as
ATP(aq) + H 2 O(l) ADP(aq) + H 2 PO 4 - (aq)
where ADP represents adenosine diphosphate. For this reaction, ∆G° = -30.5 kJ.
(a) Calculate K at 25°C.
One reaction that occurs in human metabolism is
(aq) + NH 3 (aq) ↔ (aq) + H 2 O(l)
glutamic acid
glutamine
(b) For this reaction, ∆G° = +14.0 kJ. Calculate K at 25°C.
(c) In a living cell this reaction is coupled with the hydrolysis of ATP. Calculate ∆G° and K at
25°C for the following reaction:
Glutamic acid(aq) + ATP(aq) + NH 3 (aq) ↔ Glutamine(aq) + ADP + H 2 PO 4 - (aq)
(d) Does this reaction proceed spontaneously in the forward direction Justify your
response.
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Name:_______________________________ Date:_________________ Hr:____
AP CHEMISTRY
Ch 16 – Spontaneity, Entropy, and Free Energy
QUIZ
7. (16 points) Consider the following reaction at 25°C
H 2 O(g) + Cl 2 O(g) ↔ 2 HOCl(g) K = 0.090
For Cl 2 O(g): ∆G f ° = 97.9 kJ/mol; ∆H f ° = 80.3 kJ/mol; and S° = 266.1 J/K∙mol.
(a) Calculate ∆G° for the reaction.
(b) Use bond energy values (Table 8.4 in your text, p 351) to estimate
∆H° for the reaction.
(c) Use the results from parts (a) and (b) to determine a ∆S° for the reaction.
(d) Determine values of ∆H f ° and S° for HOCl(g).
(e) Determine a value for K for the overall reaction at 500. K.
(f) Calculate ∆G at 25°C when P H2O = 18 torr, P Cl2O = 2.0 torr, and P HOCl = 30. torr.
(g) Under the conditions in part (f), is the reaction spontaneous in the forward direction
Justify your response.
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Name:_______________________________ Date:_________________ Hr:____
AP CHEMISTRY
Ch 16 – Spontaneity, Entropy, and Free Energy
QUIZ
8. (8 points) Consider the reaction: H 2 (g) + Br 2 (g) ↔ 2 HBr(g), ∆H° = -103.8 kJ. In a particular
experiment, equal moles of H 2 (g) at 10.0 atm and Br 2 (g) at 10.0 atm were mixed in a 1.00 L flask
at 25°C and allowed to reach equilibrium. Then the molecules of H 2 at equilibrium were
counted (using a very sensitive technique), and 1.10 x 10 14 molecules were found. For this
reaction, calculate the values of K, ∆G°, and ∆S°.
9. (6 points) For a solvent, Z, the enthalpy of vaporization is 16.05 kJ/mol, and the entropy of
vaporization is 45.45 J/K∙mol.
(a) Determine the boiling point (in °C) of solvent Z.
(b) Some non-electrolyte solute, X, (molar mass = 236 g/mol) was dissolved in 130.0 mL of
solvent Z (density = 0.874 g/mL). The elevated boiling point of the solution was 355.2 K.
What mass of solute X was dissolved in the solvent Z The boiling-point elevation
constant for solvent Z is 3.5 K∙kg/mol.
I affirm that the work shown on this quiz is entirely my own effort and that no resources other than those specified
were used.
____________________________________
Student Signature
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