AP Chemistry : Thermodynamics

Study concepts, example questions & explanations for AP Chemistry

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Example Questions

Example Question #71 : Thermodynamics

Using the following data to calculate the enthalpy change in:  C4H10O(l)  ->  C4H8 (g)  +  H2O (g)

01q

Possible Answers:

76 kJ/mol

-17 kJ/mol

-152 kJ/mol

152 kJ/mol

-76 kJ/mol

Correct answer:

76 kJ/mol

Explanation:

01a

Example Question #652 : Ap Chemistry

Using the following data to calculate the enthalpy change in:  CaO (s) + H2O (l)  ->  Ca(OH)2 (aq)

02q

Possible Answers:

147 kJ/mol

-147 kJ/mol

-124 kJ/mol

-62 kJ/mol

124 kJ/mol

Correct answer:

-147 kJ/mol

Explanation:

02a

Example Question #653 : Ap Chemistry

Using the following data to calculate the enthalpy change in:  B2H6 (g) + 3 O2 (g) -> B2O3 (s) + 3 H2O (l)

03q

Possible Answers:

-1084 kJ/mol

2168 kJ/mol

-2168 kJ/mol

1084 kJ/mol

3252 kJ/mol

Correct answer:

-2168 kJ/mol

Explanation:

03a

Example Question #1 : Cell Potential Under Non Standard Conditions

Consider an electrochemical cell that has the following overall reaction:

2 H+(aq) + Sn (s) -> Sn2+ (aq) + H2 (aq)

 

Which of the following changes would alter the measured cell potential?

Possible Answers:

All of the above.

Adding SnCl2 to the cathode.

Lowering the pH in the cathode.

Increase the pH in the cathode.

Increasing the H2 pressure in the cathode.

Correct answer:

All of the above.

Explanation:

All of these changes would change Q and thus change the measured cell potential.

Example Question #71 : Thermodynamics

For the following cell reaction:

 

2 Al (s) + 3 Mn2+ (aq) -> 2 Al3+ (aq)  + 3 Mn (s)

predict if the cell potential Ecell will be larger, or smaller than Eocell for the following conditions: 

[Al3+] = 2.0 M; [Mn2+] = 1.0 M. 

Possible Answers:

Identical

Larger

Smaller

Can not be determined

Correct answer:

Smaller

Explanation:

Altering these conditions would increase Q, and thus result in a decrease in the measured cell potential.

Example Question #72 : Thermodynamics

For the following cell reaction:

2 Al (s) + 3 Mn2+ (aq) -> 2 Al3+ (aq)  + 3 Mn (s)

predict if the cell potential Ecell will be larger, or smaller than Eocell for the following conditions:  [Al3+] = 1.0 M; [Mn2+] = 5.0 M. 

Possible Answers:

Larger

Can not be determined

Smaller

Identical

Correct answer:

Larger

Explanation:

At these concentrations Q will become smaller, and thus log Q will become smaller.  This will give rise to a larger cell potential.

Example Question #5 : Cell Potential Under Non Standard Conditions

What is the cell potential of the following cell:

 

Zn (s) + 2 H+(aq)  ->  Zn2+ (aq)  +  H2 (g)                                  Eo = 0.76 V

 

When the [Zn2+] = 1.0 M; PH2 = 1 atm, and the pH in the cathode is 5.2?

Possible Answers:

1.59 V

0.90 V

1.32 V

1.80 V

0.45 V

Correct answer:

0.45 V

Explanation:

Example Question #71 : Thermodynamics

Calculate the standard cell potential of the following reaction:

Cd(s) +  MnO2 (s) + 4 H+ (aq) +  ->  Cd2+ (aq) +  Mn2+ (aq)  + 2 H2O (l)

 

Given:

 

MnO2 (s) + 4 H+ (aq)  + 2e-  ->  Mn2+ (aq) + 2 H2O (l)            Eo = 1.23 V

Cd2+ (aq)  + 2 e-   ->  Cd (s)                                                     Eo = -0.40 V

Possible Answers:

 0.0 V

0.83 V

-0.83 V

1.63 V

-1.63 V

Correct answer:

1.63 V

Explanation:

Eocell  = Eo cathode - Eoanode

Eocell = 1.23 – (-0.40) = 1.63 V

Example Question #73 : Thermodynamics

Calculate the standard cell potential of the following reaction:

Zn (s) + Cu2+ (aq)  ->  Zn2+ (aq) + Cu (s)

 

Given:

Zn2+(aq)+ 2 e-->  Zn (s)                                             Eo = -0.76 V

Cu2+(aq)+ 2 e-->  Cu (s)                                             Eo = 0.34 V

Possible Answers:

 -0.42 V

0.0 V

 -1.10 V

1.10 V

0.42 V

Correct answer:

1.10 V

Explanation:

Eocell  = Eo cathode - Eoanode

Eocell = 0.34 – (-0.76) = 1.10 V

Example Question #3 : Cell Potential Under Non Standard Conditions

Calculate the standard cell potential of the following reaction:

Zn (s) + 2 Ag1+ (aq)  ->  Zn2+ (aq) + 2 Ag (s)

 

Given:

Zn2+(aq)+ 2 e-->  Zn (s)                                             Eo = -0.76 V

Ag1+(aq)+ 1 e-->  Ag (s)                                             Eo = 0.80 V

Possible Answers:

0.04 V

-0.04 V

-1.56 V

1.56 V

2.36 V

Correct answer:

1.56 V

Explanation:

Eocell  = Eo cathode - Eoanode

Eocell = 0.80 – (-0.76) = 1.56 V

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