Chem 106, Clicker Questions Which of the following involves a decrease in entropy? a. the sublimation of carbon dioxide b. the dissolution of NaCl in water c. the decomposition of N2O4(g) to 2 NO2(g) d. the evaporation of ethanol e. the freezing of liquid water into ice Copyright 2006, David R. Anderson

Chem 106, Clicker Questions Which reaction is likely to have a negative change in entropy? a. 2 NH3(g) ® N2(g) + 3 H2(g) b. CaO(s) + CO2(g) ® CaCO3(s) c. NaCl(s) ® Na+(aq) + Cl-(aq) d. N2O4(g) ® 2 NO2(g) e. NaHCO3(s) ® NaOH(s) + CO2(g) Copyright 2006, David R. Anderson

Chem 106, Clicker Questions All of the following statements concerning entropy are true except: a. entropy is zero for elements under standard conditions. b. a negative change in entropy denotes a change toward lower probability. c. a positive change in entropy denotes a change toward greater disorder. d. entropy values for substances under standard conditions are greater than zero. e. the entropy of a substance in the gas phase is greater than the solid phase. Copyright 2006, David R. Anderson

Chem 106, Clicker Questions A statement of the second law of thermodynamics is that a. spontaneous reactions are always exothermic. b. energy is conserved in a chemical reaction. c. the entropy of the universe is continually increasing. d. the enthalpy of reaction is the difference between product and reactant enthalpies. e. the Gibbs free energy is a function of both enthalpy and entropy. Copyright 2006, David R. Anderson

Chem 106, Clicker Questions If DG < 0 for a reaction at all temperatures, then DS is ________ and DH is ________. a. positive, positive b. positive, negative c. zero, positive d. negative, positive e. negative, zero Copyright 2006, David R. Anderson

Chem 106, Clicker Questions Predict the signs of DH and DS for the evaporation of water at 35ºC. a. DH > 0 and DS > 0 b. DH > 0 and DS < 0 c. DH < 0 and DS > 0 d. DH < 0 and DS < 0 e. Not enough information is provided to answer this question. Copyright 2006, David R. Anderson

Chem 106, Clicker Questions Predict the signs of DH, DS, and DG for the combustion of hydrogen gas at 25ºC.   2 H2(g) + O2(g) ® 2 H2O(l) a. DH < 0, DS < 0, DG < 0 b. DH > 0, DS > 0, DG < 0 c. DH < 0, DS > 0, DG < 0 d. DH > 0, DS < 0, DG > 0 e. Not enough information is provided to answer this question. Copyright 2006, David R. Anderson

Chem 106, Clicker Questions As CaCl2 dissolves in water, the temperature of the water increases. What are the signs of DH, DS, and DG for this process? a. DH < 0, DS < 0, DG < 0 b. DH > 0, DS > 0, DG < 0 c. DH < 0, DS > 0, DG < 0 d. DH > 0, DS < 0, DG > 0 e. Not enough information is provided to answer this question. Copyright 2006, David R. Anderson

Chem 106, Clicker Questions If DGº< 0, then a. K >1 b. K = 0 c. K < 1 d. K = 1 e. K < 0 Copyright 2006, David R. Anderson

Answers e b a c