Chapter 18--Thermodynamics
Calculate ΔG˚ at 298K for the vaporization of water. ΔH˚vap = +44kJ ΔS˚vap = +119J/K
+8.5kJ
Calculate ΔS˚ for the following reaction. 2NO(g) + Cl2(g) → 2NOCl(g) Substance S˚ (J/K) NO(g) 211 Cl2(g) 223 NOCl(g) 264
-117 J/K
Given the thermodynamic data below, what is ΔH° for the following reaction? C5H12(l) + 11/2O2(g) → 5CO(g) + 6H2O(l) ΔH°rxn = ? C5H12(l) + 8O2(g) → 5CO2(g) + 6H2O(l) ΔH°rxn = -3510 kJ CO(g) + ½O2(g) → CO2(g) ΔH°rxn = -283 kJ
-2095kJ
Calculate ΔG˚ at 298K for the following reaction. ½H2(g) + ½N2(g) + 3/2O2(g) → HNO3(g) ΔH˚ = -134kJ ΔS˚ = +266J/K @298K
-213kJ
Based upon the provided enthalpies of formation what is ΔH⁰ for the following reaction? 2C2H2(g) + 5O2(g) → 4CO2(g) + 2H2O(g) Compound ΔH⁰f C2H2(g) 227kJ CO2(g) -394kJ H2O(g) -242kJ
-2514kJ
What is ΔH° for the following reaction? C6H12O6(s) + 6O2(g) → 6CO2(g) + 6H2O(g) C6H12O6(s) -1274 CO2 -393 H2O -242
-2536kJ
Based upon the provided enthalpies of formation what is ΔH⁰ for the following reaction? 2Cu2O(s) + O2(g) → 4CuO(s) Compound ΔH⁰f Cu2O(s) -169kJ CuO(s) -157kJ
-290kJ
Based upon the provided enthalpies of formation what is ΔH⁰ for the following reaction? 2IBr(g) + Cl2(g) → 2ICl(g) + Br2(l) Compound ΔH⁰f IBr(g) 41kJ ICl(g) 18kJ
-46kJ
Given the thermodynamic data below, what is ΔH° for the following reaction? 2CO(g) + O2(g) → 2CO2(g) 2C(s) + O2(g) → 2CO(g) ΔH°rxn = -221 kJ 2C(s) + 2O2(g) → 2CO2(g) ΔH°rxn = -787 kJ
-566kJ
Given the thermodynamic data below, what is ΔH° fro the following reaction? 4A + 8B → 2D + 6E A + 2B → C ΔH° = -100kJ D + 3E → 2C ΔH° = 150kJ
-700kJ
What is Delta G equal to at standard?
0
What are the two requirements of a formation reaction?
1. Forms one mole of a single product 2. Reactants are elements in their standard states
k=
1.38×10-23J/K
Write the formation rxn for HCl
1/2 H2 + 1/2 Cl2--> HCl
Which of the following is a formation reaction? Choose only ONE best answer. A N(g) + O(g) → NO(g) B C(diamond) + O2(g) → CO2(g) C N2(g) + 3H2(g) → 2NH3(g) D C(graphite) + CO2(g) → 2CO(g) E 1/2H2(g) + 1/2N2(g) + 3/2O2(g) → HNO3(g)
1/2H2(g) + 1/2N2(g) + 3/2O2(g) → HNO3(g)
For water, ΔH°vap = 40.67kJ/mol. What is ΔS°vap for water?
109 J/K.mol Rearranging to solve for ΔS°vap (and you are expected to know that the boiling point of water is 100°C or 373K) :
Given the thermodynamic data below, what is ΔH° for the following reaction? H2O2(l) → H2(g) + O2(g) ΔH°rxn = ? H2(g) + ½O2(g) → H2O(l) ΔH°rxn = -286 kJ H2O(l) + ½O2(g) → H2O2(l) ΔH°rxn = 98 kJ
188kJ
Based upon the provided enthalpies of formation what is ΔH⁰ for the following reaction? 2SO3(g) → 2SO2(g) + O2(g) Compound ΔH⁰f SO3(g) -396kJ SO2(g) -297kJ
198kJ
Given the thermodynamic data below, what is ΔH° for the following reaction? 3Fe2O3(s) → 2Fe3O4(s) + ½O2(g) ΔH°rxn = ? 2Fe(s) + 3/2O2(g) → Fe2O3(s) ΔH°rxn = -824 kJ 3Fe(s) + 2O2(g) → Fe3O4(s) ΔH°rxn = -1120 kJ
232kJ
If a reaction has an equilibrium constant of 1.0 x 10-4 at 27˚C then what is ΔG˚? ΔG˚ = -RTlnKeq R = 8.314J/mol∙K
23kJ
For which of the following reactions is ΔS˚ < 0? Choose only ONE best answer. A H2O(l) → H2O(g) B N2O4(g) → N2(g) + 2O2(g) C H2O(s) → H2O(g) D KBr(s) → KBr(aq) E 2H2O(g) + O2(g) → 2H2O(l)
2H2O(g) + O2(g) → 2H2O(l)
What is the equilibrium constant of the following reaction at 298K? HI(aq) ↔ H+(aq) + I-(aq) ΔG˚ = -54.2kJ/mol ΔG˚ = -RTlnKeq R = 8.314J/mol∙K
3.17 x 109
Given the following standard enthalpy of formation values, calculate the Delta Hf rxn of the following reaction: PCl3(g) + 3HCl(g) → 3Cl2(g) + PH3(g) PCl3= -288.07 HCl= -92.30 PH3= 5.40
570.37 kJ
Given the thermodynamic data below, what is ΔH° for the following reaction? 2NO(g) + 3H2O(l) → 2NH3(g) + 5/2O2(g) ΔH°rxn = ? N2(g) + 3H2(g) → 2NH3(g) ΔH°rxn = -92 kJ 2H2(g) + O2(g) → 2H2O(l) ΔH°rxn = -572 kJ N2(g) + O2(g) → 2NO(g) ΔH°rxn = 180 kJ
586kJ
What is the boiling temperature of Br2? Br2(l) → Br2(g) ΔH°vap = +31kJ ΔS°vap = +93 J/K
60°C
For PCl3 ΔH˚vap = 32kJ/mol and ΔS˚vap = 95J/K. What is the normal boiling point for PCl3?
64˚C
Given the thermodynamic data below, what is ΔH° for the following reaction? Cu2S(s) → 2Cu(s) + S(s) ΔH°rxn = ? S(s) + O2(g) → SO2(g) ΔH°rxn = -297 kJ 2Cu(s) + SO2(g) → Cu2S(s) + O2(g) ΔH°rxn = 217 kJ
80kJ
3 rd Law
A perfect crystal at zero Kelvin has zero entropy.
Which of the following is true about the sublimation of CO2? Choose only ONE best answer. A It is spontaneous at low temperatures. B As temperature increases, ΔG decreases. C As temperature increases, ΔG increases. D As temperature increases, ΔG remains constant. E It is exothermic.
As temperature increases, ΔG decreases. Under such conditions a reaction is spontaneous at high temperatures and nonspontaneous at low temperatures. At a certain threshold temperature ΔG will equal zero. Below that temperature ΔG is positive and above that temperature ΔG is negative. Therefore, it can be concluded that ΔG decreases as temperature increases.
Delta G= 0
At equilibrium
For a reaction at 298K, ΔH˚ = 50kJ and ΔS˚ = 200J/K. Under what conditions would this reaction be spontaneous? (Assume ΔH˚ and ΔS˚ are constant.) Choose only ONE best answer. A At all temperatures B At temperatures below 250K C At temperatures above 250K D At temperatures below -23K E At temperatures above -23K
At temperatures above 250K
Which elements are liquids?
Br2 and Hg
What are the special elements?
C (graphite) and S8
For which of the following reactions is ΔH°rxn = ΔH°f ? Choose only ONE best answer. A Na+(aq) + Cl-(aq) → NaCl(s) B C(graphite) + 1/2O2(g) → CO(g) C Na(s) + Cl(g) → NaCl(s) D 1/2O2(g) + H2O(l) → H2O2(l) E H2(g) + N2(g) + 3O2(g) → 2HNO3(g)
C(graphite) + 1/2O2(g) → CO(g)
For which of the following processes would we expect the entropy change to be closest to zero? Choose only ONE best answer. A 2NO2(g) → 2NO(g) + O2(g) B 2CO(g) + O2(g) → 2CO2(g) C 2C(s) + O2(g) → 2CO(g) D C(s) + O2(g) → CO2(g) E 2NO(g) + O2(g) → N2O4(g)
C(s) + O2(g) → CO2(g) No change in the mols of gas
Which of the following has the greatest entropy (assume all substances are in the same phase at the same temperature)? Choose only ONE best answer. A H2O B C6H12O6 C CH4 D HF E NH3
C6H12O6 The molecule with the greatest number and variety of atoms will have the greatest number of possible microstates and the greatest entropy. C6H12O6 has the greatest number and variety of atoms and the greatest entropy.
For which of the following reactions is ΔS > 0? Choose only ONE best answer. A Na(l) → Na(s) B NH3(g) → NH3(l) C CO2(g) → CO2(s) D C6H6(s) → C6H6(l) E Ag+(aq) + Cl-(aq) → AgCl(s)
C6H6(s) → C6H6(l)
Which of the following reactions would be expected to have an entropy change closest to zero? Choose only ONE best answer. A 2Cu(s) + O2(g) → Cu2O(s) B 2NH3(g) → N2(g) + 3H2(g) C CO2(s) → CO2(g) D CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) E 2C(s) + O2(g) → 2CO(g)
CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) An increase in the number of moles of gas results in an increase in entropy (positive ΔS), whereas a decrease in the number of moles of gas will result in a decrease in entropy (negative ΔS).
For which of the following reactions is ΔS˚ > 0? Choose only ONE best answer. A 2CO(g) → 2C(s) + O2(g) B 2H2(g) + O2(g) → 2H2O(g) C CaCO3(s) → CaO(s) + CO2(g) D C6H6(l) → C6H6(s) E Ag+(aq) + Cl-(aq) → AgCl(s)
CaCO3(s) → CaO(s) + CO2(g)
For which of the following reactions is ΔS < 0? Choose only ONE best answer. A H2O(l) → H2O(g) B 2NH3(g) → N2(g) + 3H2(g) C 2C(s) + O2(g) → 2CO(g) D CaO(s) + O2(g) → CaCO3(s) E KBr(s) → KBr(aq)
CaO(s) + O2(g) → CaCO3(s)
1 st Law
Conservation of energy (Energy can't be created or destroyed).
What happens to entropy as temperature decreases?
Decreases because atoms stop moving
How to calculate Standard Delta G
Delta G standard= -RTlnKeq
How to calculate Delta G not under standard conditions
Delta G= Delta G standard +RTlnQ
What is delta S when there is an increase in complexity?
Delta S > 0
What is delta S when there is an increase in mols of gas?
Delta S > 0
A(g) + B(g) → C(g) H = -25kJ/mole Is this reaction spontaneous at all temps, no temp, low temp, or high temps?
Delta S= -, because decreasing mols of gas Delta H= -, given Spontaneous at low temperatures
What is entropy related to?
Disorder or randomness
2H2O(g) → 2H2(g) + O2(g) The reaction above is only spontaneous at temperatures above 2000K. Is the reaction endothermic (+H) or exothermic (-H)?
Endothermic
2 nd Law
For a spontaneous process, the entropy of the universe increases.
Which of the following is a statement of the 2nd Law of Thermodynamics? Choose only ONE best answer. A The entropy of a system increases for a spontaneous process B Energy can't be created or destroyed C For a spontaneous process, ΔSuniverse > 0 D Expanding gases cool E A perfect crystal at zero Kelvin has no entropy
For a spontaneous process, ΔSuniverse > 0
When Delta H rxn= Delta H f, this is what type of reaction?
Formation
In which phase changes is Delta S and H < 0?
Gas--> Liquid--> Solid
Factors affecting Entropy
Gases > Liquids > Solids
Higher Temperature= ? Entropy
Greater Entropy
Higher number of particles= ? Entropy
Greater Entropy
Higher volume= ? Entropy
Greater Entropy
Which elements are gases?
H, N, O, F, Cl, He, Ne, Ar, Kr, Xe, Rn
Which of the following shows the correct relationship between ΔG˚ and Keq? Choose only ONE best answer. A If ΔG˚ > 0, Keq < 0. B If ΔG˚ > 0, Keq > 1. C If ΔG˚ < 0, Keq = 0. D If ΔG˚ < 0, Keq > 1. E If ΔG˚ > 1, Keq < 0.
If ΔG˚ < 0, Keq > 1.
Increase in microstates of a system = What happens to entropy?
Increase
Which of the following is true regarding the following reaction? C2H2(g) + O2(g) → 2CO2(g) + 2H2O(g) ΔH˚ = -1310kJ Choose only ONE best answer. A It is spontaneous at all temperatures. B It is spontaneous at low temperatures. C It is spontaneous at high temperatures. D The reverse reaction is spontaneous at all temperatures. E It is nonspontaneous at all temperatures.
It is spontaneous at all temperatures.
Which of the following is true regarding the following reaction? 2NH3(g) → N2(g) + 3H2(g) ΔH˚ = +161kJ Choose only ONE best answer. A It is spontaneous at all temperatures. B It is spontaneous at low temperatures. C It is spontaneous at high temperatures. D The reverse reaction is spontaneous at all temperatures. E It is nonspontaneous at all temperatures.
It is spontaneous at high temperatures.
Which of the following is true regarding the following reaction? I2(g) → I2(s) ΔH˚ = -62kJ Choose only ONE best answer. A It is spontaneous at all temperatures. B It is spontaneous at low temperatures. C It is spontaneous at high temperatures. D The reverse reaction is spontaneous at all temperatures. E It is nonspontaneous at all temperatures.
It is spontaneous at low temperatures. Delta S is negative
What is Keq when Delta G standard is >0?
Keq<1
When Delta G standard < 0, what is Keq?
Keq>1
Write the formation rxn for NaHCO3
Na + 1/2 H2 + C (graphite) + 3/2 O2--> NaHCO3
For which of the following reactions is ΔS > 0? Choose only ONE best answer. A N2(g) + 3H2(g) → 2NH3(g) B NaCl(s) → NaCl(aq) C H2O(g) → H2O (l) D 1/2H2(g) + 1/2N2(g) + 3/2O2(g) → HNO3(g) E CO2(g) → CO2(s)
NaCl(s) → NaCl(aq)
What type of reaction is G>0, Keq<1
Non spontaneous, favors reactants
For which of the following phase changes is ΔH < 0 and ΔS > 0? Choose only ONE best answer. A Fusion B Sublimation C Deposition D Aggregation E None of these
None of these
Delta G>0
Nonspontaneous
Delta H= Positive Delta S= Negative TDeltaS= Positive
Nonspontaneous at all temperatures
Delta S system+ Delta S surroundings= Positive or negative
Positive
Is the delta S of the universe positive or negative?
Positive
Which of the following reactions would have the largest equilibrium constant? Choose only ONE best answer. A Reaction #1; ΔG˚ = -100kJ B Reaction #2; ΔG˚ = +200kJ C Reaction #3; ΔG˚ = -50kJ D Reaction #4; ΔG˚ = -175kJ E Reaction #5; ΔG˚ = +350kJ
Reaction #4; ΔG˚ = -175kJ
In which phase changes is Delta S and H > 0?
Solid--> Liquid--> Gas
Delta G<0
Spontaneous
Delta H= Negative Delta S= Positive TDeltaS= Negative
Spontaneous at all temperatures
Delta H= Positive Delta S= Positive TDeltaS= Negative
Spontaneous at high temperatures
Delta H= Negative Delta S= Negative TDeltaS= Positive
Spontaneous at low temperatures
What type of rxn is G<0, Keq>1
Spontaneous, favors products
For which of the following phase changes is ΔH > 0 and ΔS > 0? Choose only ONE best answer. A Freezing B Condensation C Sublimation D Deposition E All of these
Sublimation
Delta S Deg.= Of a reaction
Sum (n) S Deg. products - Sum n S Deg. reactants
Delta G Deg. = Of a reaction
Sum(n)Delta G Deg. f,products - Sum(n) Delta G Deg. f,reactants
Delta H Deg.= Of a reaction
Sum(n)Delta H Deg. f,products - Sum(n)Delta H Deg. f,reactants
Gibbs Free Energy
The energy available to do work
Which of the following is false about entropy? Choose only ONE best answer. A The greater the number of microstates of a system, the greater the entropy. B Entropy is associated with disorder. C Boiling is accompanied by an increase in entropy. D The entropy of a system always increases for a spontaneous process. E Increasing the temperature of the system will result in an increase in entropy.
The entropy of a system always increases for a spontaneous process. But the entropy of the system individually may increase or decrease.
For a certain reaction ΔG° = -850kJ/mol. Which of the following statements is FALSE concerning this reaction? Choose only ONE best answer. A This reaction is spontaneous under standard conditions B At equilibrium, there will be more products present than reactants C The equilibrium constant will be greater than 1 D The equilibrium constant will be much smaller than 1 E ΔH° - TΔS° < 0
The equilibrium constant will be much smaller than 1
Which of the following is true for the following reaction? Na(s) + ½Cl2(g) → NaCl(s) ΔG˚ = -411kJ Choose only ONE best answer. A ΔS˚ is positive. B The equilibrium constant is negative. C The products are favored at equilibrium. D The equilibrium constant is less than 1. E The reactants are lower in free energy than the products.
The products are favored at equilibrium.
Which of the following is true regarding the following reaction? 8CO2(g) + 10H2O(g) → C4H10(l) + 13O2(g) ΔH˚ = +5755kJ Choose only ONE best answer. A It is spontaneous at all temperatures. B It is spontaneous at low temperatures. C It is spontaneous at high temperatures. D The reverse reaction is spontaneous at all temperatures. E None of these is true.
The reverse reaction is spontaneous at all temperatures.
R=
Universal Gas constant, 8.314 J/mol K
In terms of mols of gas, when will Delta S be positive?
When there are more mols on the product side
Delta G=
delta H - T delta S Get higher test scores
Which of the following will result in an entropy decrease? Choose only ONE best answer. A fusion B deposition C vaporization D sublimation E melting
deposition
Which of the following processes would be accompanied by an increase in entropy? Choose only ONE best answer. A fusion B condensation C deposition D freezing E rust formation (4Fe(s) + 3O2(g) → 2Fe2O3(s))
fusion Fusion (melting) is the phase change from solid to liquid. This involves going from a phase with more order to less order and is therefore accompanied by an increase in entropy. Condensation, deposition, and freezing are all phase changes going from a phase with less order to more order and are therefore accompanied by decreases in entropy.
S=
klnW
When would the following reaction be expected to be spontaneous? 2NO(g) + O2(g) →N2O4(g) ΔH = -171 kJ Choose only ONE best answer. A low temperatures B high temperatures C all temperatures D never E Only on Fridays
low temperatures
W=
number of microstates
Which of the following is NOT a state function? Choose only ONE best answer. A ΔH˚ B ΔG˚ C ΔH D ΔS˚ E q
q The two significant quantities that are not state functions are heat (q) and work (w) as they are completely dependent upon the path taken.
Which of the following is always true for a reaction at equilibrium? Choose only ONE best answer. A K = 1 B Q = 1 C ΔH = 1 D ΔG = 0 E More than one of these
ΔG = 0
Which of the following is NOT a law of thermodynamics? Choose only ONE best answer. A A perfect crystal at zero Kelvin has zero entropy. B Energy cannot be created or destroyed. C ΔG = ΔH - TΔS D For a spontaneous process, ΔSuniverse > 0. E All of these are laws of thermodynamics.
ΔG = ΔH - TΔS is an equation of thermodynamics but isn't one of the laws of thermodynamics.
What is ΔHo for the following reaction? N2(g) + 3H2(g)--> 2NH3(g) N-H 391kJ/mol N TRPL N 941kJ/mol H-H 436kJ/mol
ΔH = [941 + 3(436)] - [6(391)] = -97kJ