Chemistry: Molecular Nature of Matter and Change, 6th Edition (Silberberg)

Chapter 20: Thermodynamics: Entropy, Free Energy, and the Direction of Chemical Reactions

Self Assessment Quiz 2

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1			For which of the following reactions is ΔS expected to be positive?
			A)	NH4Cl(s) → NH3(g) + HCl(g)
			B)	2H(g) + O(g) → H2O(g)
			C)	HCl(g) + NaOH(s) → NaCl(g) + H2O(g)
			D)	2H2(g) + O2(g) → 2H2O(g)
			E)	N2(g) + 3H2(g) → 2NH3(g)
2			Which of the following changes, all involving one mole of pure water, has the greatest ΔSsys?
			A)	raising the temperature of the solid from -10.0°C to 0.0°C
			B)	melting the solid at 0°C
			C)	raising the temperature of the liquid from 0.0°C to 10.0°C
			D)	vaporizing the liquid at 100.0°C
			E)	raising the temperature of the vapor 100.0°C to 110.0°C
3			Calculate ΔSº for the reaction C9H20(l) + 14O2(g) → 9CO2(g) + 10H2O(g) Data: Standard molar entropies, Sº in J/mol.K: C9H20(l), 393.7; O2(g), 205.0; CO2(g), 213.7; H2O(g), 188.7
			A)	-196.3 J/K
			B)	+196.3 J/K
			C)	-546.6 J/K
			D)	+546.6 J/K
			E)	+1341 J/K
4			Select the most likely standard entropy change, ΔS° for the reaction: 2H2(g) + O2(g) → 2H2O(g)
			A)	0 J/K
			B)	189 J/K
			C)	-87 J/K
			D)	+44 J/K
			E)	-5 J/K
5			Which of the following statements about entropy and enthalpy of a system is correct?
			A)	The absolute entropy of pure oxygen at 25ºC and 1 atm is zero.
			B)	When ice melts, ΔS is positive and ΔH is negative.
			C)	When a candle burns, ΔS is positive and ΔH is negative.
			D)	The entropy of a system must increase for the reaction to be spontaneous.
			E)	None of the above statements is correct.
6			Which of the following is necessary and sufficient for a process be spontaneous?
			A)	ΔG < 0
			B)	ΔSsurr > 0
			C)	ΔH < 0
			D)	ΔSsys > 0
			E)	ΔH > TΔS
7			Given the following reactions and their values of ΔG°: 2CO(g) + O2(g) → 2CO2(g) ΔG° = -516 kJ 4MnO(s) + O2(g) → 2Mn2O3(s) ΔG° = -312 kJ Calculate ΔG° for the reaction: Mn2O3(s) + CO(g) → 2MnO(s) + CO2(g)
			A)	+204 kJ
			B)	-204 kJ
			C)	+102 kJ
			D)	-102 kJ
			E)	-414 kJ
8			Methanol is used as a high performance fuel. Calculate ΔG° for the combustion reaction: 2CH3OH(l) + 3O2(g) → 2CO2(g) + 4H2O(g) Data: Standard free energies of formation, ΔG°f (kJ/mol): CH3OH(l), -163 kJ; O2(g), 0; CO2(g), -394; H2O(g), -229
			A)	+1146 kJ
			B)	+1460 kJ
			C)	-460 kJ
			D)	-945 kJ
			E)	-1378 kJ
9			Consider the reaction: C9H20(l) + 14O2(g) → 9CO2(g) + 10H2O(g) For this reaction, ΔSº is +546.6 J/K and ΔHº is -5685 kJ. Use these values to calculate ΔGº.
			A)	+5848 kJ/mol
			B)	-5848 kJ/mol
			C)	+5139 kJ/mol
			D)	-5139 kJ/mol
			E)	+4922 kJ/mol
10			In 1774 Joseph Priestley prepared the element oxygen by heating mercury(II) oxide: HgO(s) → Hg(l) + ½O2(g) For this reaction, ΔHº = 90.84 kJ and ΔSº = 108 J/K. Which of the following statements is true?
			A)	The reaction is only spontaneous at low temperatures.
			B)	The reaction is spontaneous at all temperatures.
			C)	ΔGº becomes less favorable as the temperature is raised.
			D)	The reaction is spontaneous only at high temperatures.
			E)	The reaction is spontaneous under standard conditions at 25°C.
11			Which of the following is true for an exothermic process?
			A)	qsys > 0, ΔSsurr < 0
			B)	qsys < 0, ΔSsurr < 0
			C)	qsys < 0, ΔSsurr > 0
			D)	qsys > 0, ΔSsurr > 0
			E)	Need to know ΔSsys before deciding which relationship is true.
12			The compound 1-pentanol has an enthalpy of vaporization of 55.5 kJ/mol and an entropy of vaporization of 148 J/K.mol. Calculate its approximate boiling point.
			A)	102°C
			B)	375°C
			C)	45°C
			D)	25°C
			E)	93°C
13			The following reaction occurs at 298 K: SO2(g) + NO2(g) → SO3(g) + NO(g) Data: Standard free energies of formation, ΔGºf (kJ/mol): SO2(g), -300.4; SO3(g), -370.4; NO(g), 86.7; NO2(g), 51.8 For the above reaction, which of the following conclusions is valid?
			A)	K > 1, ΔHº > 0
			B)	K > 1, ΔHº < 0
			C)	K < 1, ΔHº > 0
			D)	K < 1, ΔHº < 0
			E)	none of the above
14			Consider the reaction: N2(g) + 3H2(g) → 2NH3(g) The standard free energy change for this reaction, ΔGº, is -32.9 kJ. Calculate the equilibrium constant, K, at 25ºC.
			A)	13.3
			B)	5.8 x 105
			C)	2.5
			D)	4.0 x 10-6
			E)	9.1 x 108
15			Calculate the equilibrium constant K for the following reaction at 25°C: <a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0310402656/38229/Q20215a.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a> Data: <a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0310402656/38229/Q20215b.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (1.0K)</a>
			A)	6.85
			B)	946
			C)	1.06 x 10-3
			D)	-6.85
			E)	none of the above

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