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CHAPTER 17 BASIC HOMEWORK:

THERMODYNAMICS II

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Question 1

Which of the following processes is NOT spontaneous?

Examples of spontaneous processes

Select one:
Correct



 

    

 

Question 2

Which of the following statements is INCORRECT?

Spontaneous processes and change in energy

Select one:


Correct

 

 

 

Question 3

Which of the following statements is INCORRECT?

Spontaneous processes and change in entropy

Enthalpy versus entropy

Select one:
Correct


 
 

 

 

 

Question 4

Which of the following statements is INCORRECT?

Entropy

Select one:

Correct




 

 

 

Question 5

For which of the following reactions is there an increase in entropy (entropy of products > entropy of reactants or ΔS > 0)?

Determining the change in entropy 1

Select one or more:
Correct
Correct

 

 

 

 

Question 6

Check those pairs of molecules where the one on the right has a larger entropy. (Each pair of molecules has the same conditions. For example, both temperatures are the same.)

Select one or more:

Correct
Correct
Correct
Correct

 

 

 

Question 7

Calculate the increase of entropy in J/K when 1.3 mole of C2H5OH melts at -114oC and 1 atm. ΔHfus = 5.02 kJ/mol.
(Remember to use J and K.)

Entropy definition and calculation

Correct

 

 Explanation

ΔS= ΔH/T  = 6526 J/ (-114+273)  = 6526/159 = 41.04

5020 J/ mol * 1.3 mol  = 6526 J

 

Question 8

Calculate the increase of entropy in J/K when 3.3 mole of C2H5OH vaporization at 78oC (the boiling point at 1 atm). ΔHvap = 39.30 kJ/mol.

Entropy 2nd calculation

Correct


 

Explanation

 Did you remember to use J and K?


39300 J/mol * 3.3 mol = 129,690 J 

ΔS= ΔH/T = 129,690/351= 369.49 J/K

 

Question 9

Consider the reaction: A(g) + 2B(g) ↔ 3C(g) + 3D(s). Keq = 1,500.
[A] = 0.10 M, [B] =0.15 M, [C] = 1.10 M, and some D is present. What is Q?


Correct

 

Explanation

 Q= [C]^3/ [A][B]^2 = (1.10)^3/(0.1)(0.15)^2 = 1.331/0/00225 = 591.56

 

Question 10

For the above value of Q


Select one:



Correct

 

 

 

Question 11

Under certain condition for the reaction A → B, ΔH = -22.2 kJ and ΔS = -50 J/K. What is ΔG in J at 205 K?

Correct

 

Explanation

ΔG= ΔH-TΔS

=-22200-(205)(-50)=-11,950

 

Question 12

Check the correct statements for the above reaction.

Select one or more:
Correct


Correct

Correct

 

Explanation

 

All answers must be correct to get credit.

 

Question 13

For the reaction A → B, ΔH = -17.8 kJ and ΔS = -35 J/K. What is ΔG in J at 977 K?

ΔG = ΔH - TΔS


Correct

 

Explanation

 ΔG= ΔH-TΔS

=-17800-977(-35)=16395

 

Question 14

Check the correct statements for the above reaction.

Select one or more:

Correct


Correct


Correct

 

 

 

Question 15


Under certain condition for the reaction A → B, ΔH = 13.7 kJ and ΔS = 23 J/K. At what temperature in K is the reaction at equilibrium?

Hint given in feedback.


Correct

 

Explanation


 Solve ΔG = ΔH - TΔS for T.
Hint, what is ΔG at equilibrium?

ΔG= ΔH-TΔS

0=13700-T(23)

T=595.65

 

Question 16

Check the correct statements for the above reaction.

Select one or more:


Correct
Correct

Correct


Correct

 

Explanation


 All answers must be correct to get credit.

 

Question 17

Under certain condition for the reaction A → B, ΔH = -17.8 kJ and ΔS = -32 J/K. At what temperature in K is the reaction at equilibrium?

Hint repeated for this problem in feedback.

Correct

 

Explanation

Solve ΔG = ΔH - TΔS for T.

Hint, what is ΔG at equilibrium?

ΔG= ΔH-TΔS

0=-17800-T(-32)

T=556.25

 

Question 18

Check the correct statements for the above reaction.Select one or more:

Correct


Correct

Correct
Correct

 

 

 

Question 19

Check those statements that are true.

Standard State and thermodynamic calculations

Select one or more:
Correct
Correct

Correct
Correct
Correct

 

Explanation

Mercury is a liquid at room temperature (standard temperature).

 

Question 20


Calculate ΔSo in J/K for the following reaction:

2Fe2O3(s) + 3C(s) → 4Fe(s) + 3CO2(g)

So(Fe2O3(s)) = 87.4 J/K/mol
So(C(s)) = 5.7 J/K/mol
So(Fe(s)) = 27.3 J/K/mol
So(CO2(g)) = 213.7 J/K/mol

Detailed delta S Calculation


Correct

 

Explanation

Remember there are 3 moles of carbon dioxide, etc.


[4(27.3)+3(213.7)]-[2(87.4)+3(5.7)]

-(109.2+641.1)-[(174.8+17.1)]

=750.3-191.9

=558.4

 

Question 21


Calculate ΔGo in kJ for the following reaction:

2Fe2O3(s) + 3C(s) → 4Fe(s) + 3CO2(g)

ΔGfo(Fe2O3(s)) = -742.2 kJ/mol
ΔGfo(C(s)) = ?
ΔGfo(Fe(s)) = ?
ΔGfo(CO2(g)) = -394.4 kJ/mol

Detailed delta G calculation

Correct

 

Explanation

Remember there are 3 moles of carbon dioxide, etc.


3(-394.4) - 2(-742.2.)

-1183.2+1484.4=301.2

 

Question 22

Check the correct statement for the reduction of iron III oxide to iron.

Reminder given in general feedback.
Select one:



Correct

 

Explanation

 If ΔG. = 0 the process is at equilibrium.
If ΔG. < 0 the process is spontaneous in the forward direction or to the right.

 

Question 23

 For a certain reaction ΔGorxn = 18.4 kJ/mol. What is the equilibrium constant at 392C?


Answer: 0.0358

 

Explanation

ΔGrxn = -RTln(Keq)
Keq= e^-ΔGrxn/RT
ΔGrxn = 18.4KJ*1000= 18400J
392C=665K
R=8.31
Keq=e^((-18400)/(665*8.31))
Keq=0.0358

 

Question 24

Correctly match the following conditions.

Hint given in general feedback.


ΔGorxn << 0 Correct

ΔGorxn < 0 Correct

ΔGorxn > 0 Correct

ΔGorxn >> 0 Correct

 

Explanation

 The help for the previous problem tells you the answer.

However, you can check for yourself using the Gibb's energy equation. Try different values for the Gibb's energy or Keq at some temperature, say 300 K, and see what happens.