Entropy

1. Entropy Contributions by: John L. Falconer & Will MedlinDepartment of Chemical and Biological EngineeringUniversity of ColoradoBoulder, CO 80309-0424 Supported by the National Science Foundation

2. You have 4 balls: red, green blue, and yellow. You distribute them all into two cans. How many different ways can you do this? 4 8 12 16 None of the above

3. A gas is compressed isothermally. The entropy of the surroundings ________. increases decreases remains the same. Insufficient information.

4. What external pressure should be used in the WEC term when calculating the entropy change for isothermal compression of an ideal gas? A constant external pressure An external pressure that is always equal to the system pressure Either (A) or (B) Neither (A) or (B)

5. Air flows steadily at constant pressure through a pipe that is heated by a furnace. As air flows through the pipe, the entropy of the air _______. increases   remains the same   decreases   Insufficient information Si So

6. Which of the following systems will have the largest entropy change when the blue partition is removed? The ideal gases are initially at 1 atm. N2 Vacuum N2 O2 A C N2 N2 Vacuum O2 B D

7. Which of the following systems will have the largest entropy change when the blue partition is removed? The gases are ideal. 2 atm N2 1 atm O2 2 atm N2 Vacuum A C 3 atm N2 3 atm N2 Vacuum 1 atm O2 B D

8. When the blue partition is removed between the two ideal gases below, the change is entropy is DS = 3Rln(2). What is most correct expression for DG? ∆H-3RTln(2) ∆H-3Rln(2) -3RTln(2) 3RTln(2) ∆H+3RTln(2) 1 atm 1 molAr 2 atm 2 mol O2

9. An ideal gas undergoes two irreversible processes between state 1 and state 2. For process A, 100 kJ of work was done by the gas. For process B, 200 kJ of work was done by the gas. Which process has the larger entropy change for the gas? Process A Process B Both process have the same change in entropy of the gas 100 kJ 1 2 200 kJ 1 2

10. A gallon of hot water is mixed with a gallon of cold water in a perfectly insulated container. When the waters are mixed, the entropy _______. increases decreases  remains the same Insufficient information  

11. 1.0 mol of hot water mixes adiabatically with 1.0 mol of cold water. The entropy change of the cold water is 0.21 J/(mol•K). The entropy change of the hot water is _______. positive < -0.21 J/(mol•K) < 0.21 J/(mol•K) > 0.21 J/(mol•K) > -0.21 J/(mol•K) ΔS = 0.21 J/(mol•K) ΔS = ?

12. Insulation System Consider a completely insulated system. A reaction takes place inside the system. Therefore the system’s entropy __________. remains the same since Q = 0 increases decreases Need more information

13. Insulation System An endothermic reaction takes place in a completely insulated, closed container of fixed volume.What happens to the entropy of system? A. Increases B. Decreases C. Does not change

14. Insulation System An exothermicreaction takes place in a completely insulated, closed container of fixed volume.What happens to the entropy of system? A. Increases B. Decreases C. Does not change

15. You raise the pressure of a gas at constant temperature in a closed, adiabatic system. The entropy of the gas ___________. does not change since temperature is constant does not change since there is no heat transfer increases decreases

16. This picture shows a DNA molecule on a surface with vertical pillars on half the surface. The DNA will _______. move into the pillars more move out onto the open area stay where it is

17. Container A has 2 kg of water, and container B has 1 kg of water. Both containers are initially at 50oC. To each container, 20 kJ of heat is added. Which container has the greater total (NOT per kg water) entropy change? A B Same entropy change for both Need more information QA = 20 kJ QB = 20 kJ B A 2 kg water at 50oC 1 kg water at 50oC

18. In these piston-cylinder systems, when the red stop is removed, the ideal gas expands, and the piston moves until it hits the black stopper. Each system is adiabatic and starts at 10 atm and 25°C. Which has the largest entropy change? A B C All the same Vacuum Vacuum Vacuum A C B 2 kg 1 kg Block Piston Gas Gas Gas

19. For which does entropy increase? Constant V Constant P Both Neither Constant P Constant V

20. Which system has the highest entropy if one mole of the same ideal gas is in each piston-cylinder? A B Both have the same entropy A B 2 atm 50°C 10 atm 50°C

21. Which system has the greatest entropy change if 10 mol N2 are in each piston-cylinder, which are initially at 100°C. Both processes are reversible. A B Same change for both WA = 0 kJ WB = 50 kJ A B QB=10 kJ QA=12 kJ

22. You lower the pressure of a gas at constant temperature in a closed, adiabatic system. The entropy of the gas ___________. does not change since temperature is constant does not change since there is no heat transfer increases decreases

23. Which is the best approximation to a constant pressure process for a gas on a H-S diagram? H H H H A D C B S S S S

24. S S S S S yi yi yi yi yi Which is the correct plot of entropy of the system (S) vs. mole fraction of component i (yi) for a binary mixture of ideal gases? A B C D E

25. A gas goes from states A to B in a reversible adiabatic process. It then goes from B back to A by a different pathway that is irreversible and not adiabatic. The entropy change for the gas for the irreversible pathway is _______ zero. greater than less than equal to A P Irrev. B V Rev.

26. Which line most likely corresponds to a constant entropy process? C B A Pressure D E Enthalpy

27. One mol of CH4 at 1 bar and 50°C is mixed with 1 mol of O2 at 1 bar and 50°C. The final mixture is at 2 bar and 50°C. Assume ideal gases. The Gibbs free energy change is ___________. positive negative zero

28. Gibbs (J/g) Which is the most correct plot of Gibbs free energyversus temperature for a single component? 0 0 0 Gibbs (J/g) Gibbs (J/g) Gibbs (J/g) A C B T-sat T-sat T-sat T(K) T(K) T(K) 0 0 Gibbs (J/g) D E T-sat T-sat T(K) T(K)

29. Gibbs (J/g) Which is the most correct plot of Gibb’s free energy versus pressure for a single component? 0 0 0 Gibbs (J/g) Gibbs (J/g) Gibbs (J/g) A C B P-sat P-sat P-sat P(atm) P(atm) P(atm) 0 0 Gibbs (J/g) D E P-sat P-sat P(atm) P(atm)

30. Two of these plots represent enthalpy and entropy vs. temperature for a pure component going from liquid to vapor. Identify the correct axes labels. Y = S ; Z = H W = S ; X = H W = H ; X = S Z = H ; X = S R = H ;Z = S W Z X Y R T(K) T(K) T(K) T(K) T(K)

31. For an ideal gas, if the pressure is increased while keeping the entropy constant, the enthalpy ________. increases decreases remains the same Need more information.

32. Two different paths can be used for a process that changes the state of a fluid from 300 K and 1 bar to 500 K and 9 bar. Path A is adiabatic and reversible, and Path B is non-adiabatic and irreversible. Which of the following statements is true? The change in entropy of the fluid will be greater for path A The change in entropy of the fluid will be greater for path B Both paths will have the same change in entropy of the fluid, but the change will be positive The compression in path A will require less work

33. Hydrogen storage often involves the sorption of hydrogen from the gas phase into a solid material, where it can be stored more densely. For the adsorption/desorption process involved in H2 storage, which process should be run at a lower temperature? Adsorption of hydrogen into material. Desorption of hydrogen from material. It does not matter.