Entropy, Spontaneity, and Free Energy Flashcards

Flashcards covering entropy, spontaneity, free energy, and related calculations based on General Chemistry II lecture notes.

Which has higher entropy: Liquid water or gaseous water?

Liquid water < gaseous water

Which has the greatest standard molar entropy (S°)? a. NH3(g) b. He(g) c. C(s, graphite) d. H2O(l) e. CaCO3(s)

NH3(g)

Which has the lowest standard molar entropy (S°)? a. CH4(g) b. CH3CH2OH() c. H2O(s) d. Na(s) e. He(g)

Na(s)

Which of the following has the highest entropy at 298 K? a. 0.5 g of HCN b. 1 mol of HCN c. 2 kg of HCN d. 2 mol of HCN

2 kg of HCN

Which one of the following reactions result in a positive ΔSsys? a. AgNO3(aq) + NaCl(aq) D AgCl(s) + NaNO3(aq) b. H2O (g) + CO2 (g) D H2CO3 (aq) c. H2(g) + I2(g) D 2 Hl(g) d. C2H2O2(g) D 2 CO(g) + H2(g) e. H2O(g) D H2O(l)

C2H2O2(g) D 2 CO(g) + H2(g)

Which one of the following reactions results in a negative ΔSsys? a. H2O(g) D H2O(s) b. CaCO3(s) D CaO(s) + CO2(g) c. CuSO4(H2O)5 (s) D CuSO4(s) + 5H2O(g) d. 14O2(g) + 3NH4NO3(s) + C10H22(l) → 3N2(g) + 17H2O(g) + 10CO2(g) e. CO2(aq) D CO2(g)

H2O(g) D H2O(s)

Which of the following processes will lead to a positive change in the entropy of the system? a. Sodium chloride crystals form as saltwater evaporates. b. Helium gas escapes from the hole in a balloon. c. Stalactites form in a cave. d. Water freezes in a freezer.

Helium gas escapes from the hole in a balloon.

Which of the following processes will lead to a decrease in the entropy of the system? a. Salt crystals dissolve in water. b. Air escapes from a hole in a balloon. c. Iron and oxygen react to form rust. d. Ice melts in your hand.

Iron and oxygen react to form rust.

Determine ΔS for H2(g) + I2(g) D 2HI(g) given the following information. Substance S° (J/mol · K) H2(g) 130.58 I2(g) 116.73 HI(g) 206.3

+165.29 J/mol · K

Determine ΔS for N2O4(g) D 2NO2(g) given the following information. Substance S° (J/mol · K) N2O4(g) 304.3 NO2(g) 240.45

+176.7 J/mol · K

What is the entropy change to make 1 mole of SO3 for the reaction SO2(g) + 1/2 O2(g) → SO3(g)? Substance S° (J/mol · K) SO2(g) 248.2 O2(g) 205.0 SO3(g) 256.8

–93.9 J/K

NO gas is converted to NO2 gas according to the following reaction, NO(g) + 1/2 O2(g) → NO2(g). What is the standard entropy change when 0.5 mol of NO gas reacts with 0.5 mol of O2 gas? Substance S° (J/mol · K) NO(g) 210.7 O2(g) 205.0 NO2(g) 240.0

–36.6 J/K

If 3.500 g of Ni (58.69 g/mol)are reacted with excess oxygen to form nickel oxide (NiO) under standard state conditions, what is the entropy change for the reaction? 2Ni(s) + O2 D 2NiO(s). Substance S° (J/mol · K) Ni 182.1 O2 205.0 NiO 37.99

–14.7 J/K

What is the entropy change if 4.500 g of CaCO3(s) is placed in a container and allowed to decompose to CaO(s) and CO2(g) according to the following reaction? CaCO3(s) D CaO(s) + CO2(g). Substance S° (J/mol · K) CaCO3(s) 92.88 CaO(s) 39.75 CO2(g) 213.6

+7.2 J/K

What is the standard entropy change when 10.0 g of methane reacts with 10.0 g of oxygen? CH4(g) + 2O2(g) → CO2(g) + 2H2O(). Substance S° (J/mol · K) CH4(g) 186.2 O2(g) 205.0 H2O(l) 70.0 CO2(g) 213.6

–37.9 J/K

In a spontaneous process, which of the following always increases? a. the entropy of the system b. the entropy of the surroundings c. the entropy of the universe d. the entropy of the system and the universe e. the entropy of the system, surroundings and the universe

the entropy of the universe

Processes are always spontaneous, regardless of temperature, when __ (H and S refer to the system). a. ΔH > 0 and ΔS < 0 b. ΔH < 0 and ΔS < 0 c. ΔH > 0 and ΔS > 0 d. ΔH < 0 and ΔS > 0

ΔH < 0 and ΔS > 0

The dissolution of ammonium nitrate in water is a spontaneous endothermic process. It is spontaneous because the system undergoes __ a. a decrease in enthalpy. b. an increase in entropy. c. an increase in enthalpy. d. a decrease in entropy. e. an increase in free energy.

an increase in entropy.

Which of the following must be true for a spontaneous exothermic process? a. only that ΔSsys < 0 b. only that ΔSsys > 0 c. both ΔSsys < 0 and the magnitude of ΔSsys < the magnitude of ΔSsurr d. both ΔSsys < 0 and the magnitude of ΔSsys > the magnitude of ΔSsurr e. either ΔSsys > 0, or else ΔSsys < 0 but the magnitude of ΔSsys < the magnitude of ΔSsurr

either ΔSsys > 0, or else ΔSsys < 0 but the magnitude of ΔSsys < the magnitude of ΔSsurr

Suppose a chemical reaction is found to be spontaneous, but with ΔSsys < 0. Which of the following statements must be TRUE? a. ΔSsurr < 0 and its magnitude is < ΔSsys. b. ΔSsurr < 0 and its magnitude is > ΔSsys. c. ΔSsurr > 0 and its magnitude is < ΔSsys. d. ΔSsurr > 0 and its magnitude is > ΔSsys.

ΔSsurr > 0 and its magnitude is > ΔSsys. In other words, the system loses entropy but the surroundings gain entropy, and the gain by the surroundings outweighs the loss by the system.

Any reaction will be spontaneous if __ a. ΔGsys > 0 b. ΔGsys < 0 c. ΔSsys > 0 d. ΔSsys < 0 e. ΔHsys < 0

ΔGsys < 0

What is the ΔGrxn for the reaction given: CH4(g) + 2O2(g) D CO2(g) + 2H2O(g). Substance ΔGform (kJ/mol) CH4(g) 50.8 CO2(g) 394.4 H2O(g) –228.57

–113 kJ/mol

Determine ΔGrxn for C4H10(l) + 13/2 O2(g) D 4CO2(g) + 5H2O(g) given the following. Substance ΔGform (J/mol · K) C4H10(l) –15.0 CO2(g) –394.4 H2O(g) –228.57

–2705 kJ/mol

Given the following data, determine the molar free energy of combustion for propane gas, C3H8. ΔG (C3H8, g) –23.5 kJ/mol ΔG (CO2, g) –394.4 kJ/mol ΔG (H2O, g) –105.6 kJ/mol

–1582.1 kJ/mol

Hydrogen reacts with nitrogen to form ammonia (NH3) according to the reaction 3H2(g) + N2(g) D 2NH3(g). The value of ΔH° is –92.38 kJ/mol, and that of ΔS° is –198.2 J/mol · K. Determine ΔG° at 25°C.

–33.32 kJ/mol

Hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH) to form sodium chloride (NaCl) and water. If ΔH° = – 56.13 kJ/mol and ΔS° = 79.11 J/mol · K, what is ΔG° for this reaction at 20°C?

–79.31 kJ/mol

A reaction is at equilibrium at a given temperature and constant pressure when __ a. ΔSrxn = 0. b. ΔS = 0. c. ΔGrxn = 0. d. ΔG = 0. e. ΔHrxn = 0.

ΔGrxn = 0.

Which of the following statements about equilibrium are true? I. ΔGsys = 0 II. ΔSsys = 0 III. ΔSuniverse = 0 a. I only b. II only c. III only d. Both I and II e. Both I and III

Both I and III

A reaction with a low enthalpy of reaction value is not spontaneous at low temperature but becomes spontaneous at high temperature. What are the signs for ΔH° and ΔS°, respectively? a. +, – b. –, – c. –, + d. +, +

+, +

The enthalpy of fusion for benzene (C6H6, 78.0 g/mol) is 127.40 kJ/kg, and its melting point is 5.5°C. What is the entropy change when 1 mole of benzene melts at 5.5°C?

35.7 J/K

The entropy of vaporization of water is 109.0 J/mol · K. What is the enthalpy of vaporization of water at its normal boiling point of 100°C?

+40.66 kJ/mol

The enthalpy and entropy of vaporization of ethanol are 38.6 kJ/mol and 109.8 J/mol · K, respectively. What is the boiling point of ethanol, in °C?

78.5°C

Dinitrogen tetroxide (N2O4) decomposes to nitrogen dioxide (NO2). If ΔH° = 58.02 kJ/mol and ΔS° = 176.1 J/mol · K, at what temperature are reactants and products in their standard states at equilibrium?

+56.5°C