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Characteristics of Ssurr The sign of Ssurr depends on whether the

reaction or process is exothermic (Ssurr >0 or “favorable”) or endothermic (Ssurr < 0 or “unfavorable”).

The magnitude of Ssurr depends on the temperature. To increase the effect of Ssurr , lower the

temperature. To decrease the effect of Ssurr , raise the

temperature. LeChatelier’s principle!

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Another Question to Consider

Calculate S and Suniv when 50.0 g of ice at 0C is dropped into 100.0 g of water at 75C in a perfectly insulated vessel and briefly discuss these numbers to show that all of the ice will indeed spontaneously melt. Hfusion for ice is 6.02 kJ/mol at 0C and Cp for water is 75.3 J/KmolAssume Cp is constant over the temperature range in question.

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Clicker QuestionA stable diatomic molecule spontaneously forms from its atoms at constant pressure and temperature. How does temperature affect the reaction?

a) An increase in temperature makes the reaction more favorable.

b) An increase in temperature makes the reaction less favorable.

c) We cannot tell from the information we know.

d) I do not know.

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Clicker QuestionConsider the spontaneous reaction:

2KClO3(s) 2KCl(s) + 3O2(g)

Is the reaction endothermic or exothermic?

a) Endothermic b) Exothermicc) More information is needed.d) I do not know.

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The meaning of Grxn

At constant temperature and pressure the sign indicates the spontaneity of the reaction. Grxn < 0 means spontaneous Grxn > 0 means not spontaneous (or spontaneous in

the opposite direction) If we change the temperature we can change the sign

of Grxn

The magnitude of Grxn tells us the relative extent of the reaction. If we change the temperature we can change the

magnitude of Grxn.

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Determining Grxn

2CO(g) + O2(g) 2CO2(g)

Consider:1. Predict if S° is positive or negative (we will determine it next).2. Predict if the reaction is exothermic or endothermic (we will determine it next).3. Can we predict the sign of G°?4. At what temperatures is this reaction spontaneous?

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Determining Grxn

2CO(g) + O2(g) 2CO2(g) G (kJ/mol) -137 0 -394 H (kJ/mol) -110.5 0 -393.5S (J/Kmol) 198 205 214

Consider:1. Predict if S° is positive or negative (then determine it).2. Predict if the reaction is exothermic or endothermic (then determine it).3. Determine G° two ways.4. At what temperatures is this reaction spontaneous?

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Chapter 10: #130One mole of a monatomic ideal gas (for which S = 8.00 J/Kmol at –73.0°C) was heated at a constant pressure of 2.00 atm from –73.0°C to 27.0°C.

Calculate ΔH, ΔE, w, q, ΔS due to the change in volume, ΔS due to the change in temperature, and ΔG. 

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Clicker QuestionGiven the following data, determine the boiling point of methanol (CH3OH).

Hf (kJ/mol) S (J/Kmol)CH3OH(g) -201 240CH3OH(l) -239 127

a) 63 K b) 63Cc) 336Cd) 1198 Ke) None of these

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Recall: Questions To Consider

Why do systems reach equilibrium? That is, why doesn’t the ball go all the way down the hill?

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Free energies change as a reaction progresses

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“Ball on a Hill”: Gibbs Free Energy

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The change in free energy to reach equilibrium

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Clicker Question

Given the following data, determine the equilibrium constant for the “pop bottle” reaction at 25C.

2H2(g) + O2(g) 2H2O(g) G (kJ/mol) 0 0 -237

a) 3.50 x 1041

b) 1.22 x 1083

c) 8.17 x 10-84

d) 2.86 x 10-42

e) I do not know how to do this problem.

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Exothermic vs. Endothermic

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Chapter 10: #139Benzene (C6H6) has a melting point of 5.5C and an enthalpy of fusion of 10.04 kJ/mol at 25.0C. The molar heat capacities at constant pressure for solid and liquid benzene are 100.4 J/Kmol and 133.0 J/Kmol, respectively. For the process:

C6H6(l) C6H6(s)

Calculate ΔS and ΔSsurr at 10.0C (and explain the significance of the results). 

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Clicker Question 102SO2(g) + O2(g) 2SO3(g).

G (kJ/mol) -290 0 -371 H (kJ/mol) -391 0 -396S (J/Kmol) 143 205 257

Determine the value of K at 25C.

a) 8 x 1024

b) 1c) 1 x 10-25

d) I know how to do this but I am not getting any of the above answers.

e) I do not know how to do this problem.

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Clicker Question 112SO2(g) + O2(g) 2SO3(g).

Knowing that G= -142 kJ/mol for the above reaction, predict the direction the system will shift to reach equilibrium if the system has the initial conditions: P(SO2) = 0.10 atm, P(O2) = 0.20 atm, and P(SO3) = 5.0 atm.

a) Shifts to the left.b) Shifts to the right.c) The reaction is at equilibrium with

those initial conditions.

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Clicker Question 122SO2(g) + O2(g) 2SO3(g).

Knowing that G= -142 kJ/mol for the above reaction, determine P(O2) so that the system is at equilibrium if P(SO2) = P(SO3).

a) 0.94 atmb) 1.3 x 10-25 atm.c) 3.0 x 10-2 atmd) I know how to do this but I am not getting

any of the above answers.e) I do not know how to do this problem.

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Clicker QuestionConsider the spontaneous reaction:

N2(g) + 3H2(g) 2NH3(g)

Is the reaction endothermic or exothermic?

a) Endothermic b) Exothermicc) More information is needed.d) I do not know.

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Consider This!2KClO3(s) 2KCl(s) + 3O2(g).

G (kJ/mol) -290 -408 0 H (kJ/mol) -391 -436 0S (J/Kmol) 143 83 205

At what temperatures is this reaction spontaneous?

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Clicker Question

Is ____ a state function?

Ssurr Suniv

a) Yes Yesb) NoNoc) Yes Nod) NoYes