Unit 9 Progress Check FRQ ANS.pdf (2024)

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1. For parts of the free-response question that require calculations, clearly show the method used

and the steps involved in arriving at your answers. You must show your work to receive creditfor your answer. Examples and equations may be included in your answers where appropriate.

Answer the following questions related to .

Substance at

(a) Using the information in the table above, determine the value of at for theprocess represented by the equation .

Please respond on separate paper, following directions from your teacher.

(b) Considering your answer to part (a), indicate whether the process is thermodynamicallyfavorable at . Justify your answer.

Please respond on separate paper, following directions from your teacher.

Water vapor can be produced in two different processes, as represented below.

Process 1 Process 2

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water, explain why the change in entropy, , is greater for process 1 than for process 2.

Please respond on separate paper, following directions from your teacher.

Part (a)

Select a point value to view scoring criteria, solutions, and/or examples and to score the response.

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The response includes both the following criteria:

Part (b)

Select a point value to view scoring criteria, solutions, and/or examples and to score the response. Theanswer to part (b) must be consistent with part (a). If a student makes an error in a previous part of thequestion, the student can still earn credit in a later part if the incorrect answer is used correctly.

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The response indicates that the process is not thermodynamically favorable at because ispositive.(OR, if part (a) indicates a negative value of ,the response indicates that the process isthermodynamically favorable because is negative.)

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Select a point value to view scoring criteria, solutions, and/or examples and to score the response.

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The response indicates that even though the process is not thermodynamically favorable, it does notfollow that the process does not occur at all. At equilibrium, the reactant (liquid water) is favored over theproduct (water vapor). This does not mean that some of the liquid water cannot evaporate to becomewater vapor.

Part (d)

Select a point value to view scoring criteria, solutions, and/or examples and to score the response.

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The response indicates that the change in entropy between ice, , and water vapor, , isgreater because the entropy of water in the solid phase, with molecules bound in fixed positions within thesolid, is less than the entropy of water in the liquid phase, with molecules able to move more freely andform a greater number of spatial configurations. Water in the gas phase, with molecules much moredispersed and even more free to move, has the highest entropy of the three phases. Therefore, process 1(sublimation) involves a greater change in entropy than process 2 (evaporation from a liquid) does.

2. For parts of the free-response question that require calculations, clearly show the method used

and the steps involved in arriving at your answers. You must show your work to receive creditfor your answer. Examples and equations may be included in your answers where appropriate.

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A chemist wants to produce from a sample of pure according to reaction 1,represented by the equation above.

(a) Using the data in the following table, calculate the value of the standard entropy change,, for the reaction.

Substance Absolute Entropy at

3320543

Please respond on separate paper, following directions from your teacher.

(b) Given that for reaction 1 is positive , what must be true about the signof for the reaction? Justify your answer.

Please respond on separate paper, following directions from your teacher.

The decomposition of into and is not a thermodynamically favoredreaction. However, to produce from , the chemist decides to pass gasover the as it is heated strongly, as represented below.

Reaction 2:

Please respond on separate paper, following directions from your teacher.

A third chemical reaction is represented below.

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(d) Show how a combination of reaction 1 and reaction 3 can be used to produce reaction 2.

Please respond on separate paper, following directions from your teacher.

(e) Determine the value of for reaction 2.

The chemist takes the produced from reaction 2 and uses it to make an electrode in agalvanic cell, as shown in the following diagram.

Please respond on separate paper, following directions from your teacher.

(f) Using the reduction half-reactions in the table below, write a balanced net-ionic equationrepresenting the overall reaction that takes place as the cell operates.

Half-Reaction (volts)

0.3370.800

Please respond on separate paper, following directions from your teacher.

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Please respond on separate paper, following directions from your teacher.

(h) Determine the value of for the cell reaction.

Please respond on separate paper, following directions from your teacher.

Part (a)

Select a point value to view scoring criteria, solutions, and/or examples and to score the response.

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The response includes the both the following set up and calculation:

Part (b)

Select a point value to view scoring criteria, solutions, and/or examples and to score the response.

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The response indicates that the sign of for the reaction must be positive becauseimplies that . In other words, if and are positive,then must also be positive.

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Part (c)

Select a point value to view scoring criteria, solutions, and/or examples and to score the response.

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The response meets both of the following criteria:

The response indicates that the reaction is a redox (or oxidation/reduction) reaction.

The response indicates that is reduced (oxidation state changes from to ) and isoxidized (oxidation state changes from to ).

Part (d)

Select a point value to view scoring criteria, solutions, and/or examples and to score the response.

0 1

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Part (e)

Select a point value to view scoring criteria, solutions, and/or examples and to score the response.

0 1

The response indicates that

Part (f)

Select a point value to view scoring criteria, solutions, and/or examples and to score the response. Note:phases after species are not necessary for full credit.

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The response indicates that the equation is

Part (g)

Select a point value to view scoring criteria, solutions, and/or examples and to score the response.

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Part (h)

Select a point value to view scoring criteria, solutions, and/or examples and to score the response.

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The response includes both the following set up and calculation:

References

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