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AP Chemistry Unit 9: Applications of Thermodynamics

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Unit 9: Applications of Thermodynamics

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Question 1

How many grams of copper are deposited when a current of $2.00 A$ passes through a $CuS O_{4}$ solution for $1.00 hour$ ? ( $M (Cu) = 63.5 g/mol$ ; $F = 96, 485 C/mol$ ; Cu deposits as Cu $^{2 +} + 2 e^{-} \to Cu$ )

2.37 g

4.74 g

0.75 g

9.48 g

Question 2

Which of the following processes has a positive entropy change ( $Δ S > 0$ )?

H_{2} O (l) \to H_{2} O (s)

(freezing)B.

N_{2} (g) + 3 H_{2} (g) \to 2 N H_{3} (g)

NaCl (s) \to N a^{+} (aq) + C l^{-} (aq)

C O_{2} (g) \to C O_{2} (s)

(dry ice)

Question 3

For a reaction with $Δ H = + 120 kJ/mol$ and $Δ S = + 400 J/ (mol \cdot K)$ , at what temperature does the reaction become spontaneous?

A.Always spontaneous, regardless of temperature.B.Above

300 K

C.Below

300 K

D.Never spontaneous, because

Δ H > 0

Question 4

In an electrolytic cell, which statement correctly describes the process?

A.A spontaneous reaction drives electron flow through the external circuit.B.External electrical energy forces a non-spontaneous redox reaction.C.The anode is negative; the cathode is positive.D.Both oxidation and reduction occur at the same electrode.

Question 5

The relationship between standard cell potential and Gibbs free energy is $Δ G^{\circ} = - n F E_{cell}^{\circ}$ , where $F = 96, 485 C/mol$ . For a cell with $E^{\circ} = + 0.50 V$ and $n = 2$ , what is $Δ G^{\circ}$ ?

+ 96.5 kJ/mol

- 96.5 kJ/mol

- 48.2 kJ/mol

- 1.00 kJ/mol

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Question 6

For a spontaneous process at constant temperature and pressure, which condition must be met?

Δ H < 0

onlyB.

Δ S > 0

onlyC.

Δ G = Δ H - T Δ S < 0

Δ H < 0

and

Δ S < 0

simultaneously

Question 7

In a galvanic (voltaic) cell, which statement correctly describes the anode and cathode?

A.Oxidation occurs at the cathode; reduction at the anode.B.Reduction occurs at the cathode; oxidation at the anode.C.Both electrodes undergo oxidation simultaneously.D.The cathode is the positive electrode in both galvanic and electrolytic cells.

Question 8

For the reaction $A \to B$ , $Δ H = - 50 kJ/mol$ and $Δ S = - 100 J/ (mol \cdot K)$ . Which statement is correct about spontaneity?

A.Always spontaneous because

Δ H < 0

.B.Never spontaneous because

Δ S < 0

.C.Spontaneous at low temperature; non-spontaneous at high temperature.D.Non-spontaneous at all temperatures because both

Δ H < 0

and

Δ S < 0

Question 9

In which of the following does the reaction become spontaneous as temperature increases from low to high?

Δ H = - 80 kJ

Δ S = - 200 J/K

Δ H = + 60 kJ

Δ S = + 150 J/K

Δ H = - 60 kJ

Δ S = + 150 J/K

Δ H = + 80 kJ

Δ S = - 200 J/K

Question 10

Which of the following correctly ranks the entropy of three states of water at the same temperature?

S (ice) > S (water) > S (steam)

S (steam) > S (water) > S (ice)

S (water) > S (steam) > S (ice)

D.All three have equal entropy at the same temperature.

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Question 11

The standard Gibbs free energy is related to the equilibrium constant by $Δ G^{\circ} = - R T ln K$ . If $Δ G^{\circ} = 0$ , what is $K$ ?

K = 0

K = 1

K = \infty

K = e

Question 12

Calculate the standard cell potential $E_{cell}^{\circ}$ for the reaction:

$Zn (s) + C u^{2 +} (aq) \to Z n^{2 +} (aq) + Cu (s)$

Given: $E_{red}^{\circ} (C u^{2 +} /Cu) = + 0.34 V$ ; $E_{red}^{\circ} (Z n^{2 +} /Zn) = - 0.76 V$

- 1.10 V

+ 1.10 V

+ 0.42 V

+ 0.34 V

AP Chemistry Unit 9: Applications of Thermodynamics — Free with Answer Explanations | Test Practice Hub