Name ______

Homework #7 Summer 2016

THERMODYNAMICS

(Assume R = 8.314 J mol-1K-1)

1. What is the first law of thermodynamics?

2. List the types of motion that the nuclei can have in the molecules of a gas or liquid

3. What are the source(s) of the potential energy in molecules?

4. Does the first law of thermodynamics predict the direction of spontaneous processes?

5. In a chemical reaction the enthalpy change is measured using calorimetry, what is the source of the enthalpy change, why is the internal energy changing?

6. Calculate the standard enthalpy change, ΔHo, for the formation of 1 mol of strontium carbonate (the material that gives the red color in fireworks) from its elements.

7. Which of the following statements could be used to define the first law of thermodynamics?

  1. Heat flows from a hot body to a cold body
  2. Energy cannot be created or destroyed but can only change from one form to another
  3. The absolute entropy of a crystal at 0K is zero
  4. In a spontaneous process Suniv < 0

8. Which of the following statements is consistent with the second law of thermodynamics?

  1. Heat flows from a hot body to a cold body
  2. Energy cannot be created or destroyed but can only change from one form to another
  3. The absolute entropy of a crystal at 0K is zero
  4. In a spontaneous process Suniv < 0

9. Which of the following statements is a definition of the third law of thermodynamics?

  1. Heat flows from a hot body to a cold body
  2. Energy cannot be created or destroyed but can only change from one form to another
  3. The absolute entropy of a crystal at 0K is zero
  4. In a spontaneous process Suniv < 0

10. Are Exothermic reactions spontaneous?

  1. Always
  2. Never
  3. Sometimes

11. Are Endothermic reactions spontaneous?

  1. Always
  2. Never
  3. Sometimes

12. Are reactions in which ΔSuniv > 0 spontaneous?

  1. Always
  2. Never
  3. Sometimes

13. Are reactions in which ΔSuniv < 0 spontaneous?

  1. Always
  2. Never
  3. Sometimes

14. Are reactions in which ΔGsys > 0 spontaneous?

  1. Always
  2. Never
  3. Sometimes

15. Are reactions in which ΔGsys < 0 spontaneous?

  1. Always
  2. Never
  3. Sometimes

16. Are reactions in which ΔSsys > 0 spontaneous?

  1. Always
  2. Never
  3. Sometimes

17. Which of the following statements is false?

  1. Entropy can be considered a measure of energy dispersal per Kelvin
  2. S = -k ln(W)
  3. G = H-TS
  4. Ssurr= -Hsys/T
  5. The entropy of the universe is always increasing

18. The spontaneous melting of ice at room temperature is

  1. An enthalpy driven process
  2. An entropy driven process
  3. Neither a or b

19. The dissolution of NaCl in water NaCl(s)  Na+(aq) + Cl-(aq) is

  1. An enthalpy driven process
  2. An entropy driven process
  3. Neither a or b

20. For the process C6H6(l) C6H6(g)

  1. S < 0
  2. S > 0
  3. S = 0
  4. Depends on the temperature
  5. Impossible to say

21. For the process 4Al(s)+3O2(g)2Al2O3(s)

  1. S < 0
  2. S > 0
  3. S = 0
  4. Depends on the temperature
  5. Impossible to say

22. For the process 2O2(g)+N2(g) 2NO2(g)

  1. S < 0
  2. S > 0
  3. S = 0
  4. Depends on the temperature
  5. Impossible to say

23. What is ΔS for the reaction at 25oC

2SO2(g) + O2(g)  2SO3(g)

given

S0 (j/K/mol)
SO2(g) / 248.1
O2(g) / 205.3
SO3(g) / 256.6
  1. -188.3 JK-1mol-1
  2. +188.3 JK-1mol-1
  3. -196.8 JK-1mol-1
  4. +196.8 JK-1mol-1
  5. none of the above

24. Which allotrope of C will have the highest entropy?

a. Diamond

b. Graphite

c. neither since Diamond and Graphite will have the same entropy

25. Consider 1 mol of H2O which will have the greatest entropy

a. Ice

b. liquid water

c. water vapor

d. They are all the same

26. Which will have the larger entropy?

a. 1 mole of KClO3(aq)

b. 1 mole of KClO3(s)

c. neither

27. Which will have the larger entropy?

a. 1 mole of Argon gas (molar mass 39.948 g/mol)

b. 1 mole of NO gas (molar mass 30.006 g/mol)

c. impossible to say

Borax (Na2[B4O5(OH)4].8H2O) is soluble in water

Na2[B4O5(OH)4].8H2O(s) ↔ 2 Na+ (aq) + [B4O5(OH)4]2- (aq) + 8 H2O (l)

The solubility product Ksp = [Na+]2[B4O5(OH)42-] is measured at temperatures ranging from 15 – 55 oC. A graph is made of ln(Ksp) vs. 1/T (see below) it is found to follow a straight line

ln(Ksp) = -12406(1/T) + 37.88

Where T is in Kelvin

28. What is the enthalpy Ho for this process?

  1. -12.406 kJ/mol
  2. +12.406 kJ/mol
  3. 103.14 kJ/mol
  4. -103.14 kJ/mol
  5. 37.88 J/mol

29. What is the entropy changeSo for this process

  1. 37.88 J/(mol.K)
  2. -37.88 J/(mol.K)
  3. -12.406 J/(mol.K)
  4. 314.93 J/(mol.K)
  5. -314.93 J/(mol.K)

30. Consider the reaction for the oxidation of SO2(g) at 25oC and 1 atm

2SO2(g) + O2(g)  2SO3(g)

The relevant thermodynamic data for this process is given in the table below

  1. Calculate ΔHo (6 marks)
  1. Is the process exothermic or endothermic? (2 marks)
  1. Calculate , ΔSo (6 marks)
  1. Calculate ΔGo (6 marks)
  1. Above what temperature would you expect this to be non-spontaneous? (6 marks)
  1. Estimate the equilibrium constant and the position of the equilibrium for the above reaction at 400oC (6 marks)

EXTRA CREDIT QUESTION ON BOLTZMAN’S LAW OF ENTROPY

Consider the figure right. Let us assume there is 1 mole of Argon gas in vessel B at the beginning.

  1. By treating each atom as either being in vessel A or B come up with W the number of possibilities where half the atoms are in vessel A and half in vessel B. (Assume the every possible arrangement of the atoms in the system is equivalent)
  1. Compare your answer to the number of possibilities where the all of the atoms end up in vessel B
  1. Calculate S for this process using Boltzmann’s Equation
  1. Does your answer show that the process in the figure is spontaneous? (Explain)
  1. Prove that the configuration with the atoms split 50:50 between A and B the most probable configuration

Hint: If I have N particles and I want the probability that p are in vessel A, the number of permutations Wp are

Where N! = N x (N-1) x (N-2) x (N-3)…. x 2 x 1

Also you may find it helpful to use Sterling’s approximation, which states that for large values of N

Have fun!