Question 1

A reaction occurs in a closed system at constant pressure and releases heat to the surroundings. Which of the following statements is correct regarding the sign of $$\Delta H$$ and the spontaneity of the reaction?

Accepted Answer

$$\Delta H is $$negative; the reaction is spontaneous.

Question 2

Which of the following best describes the entropy change ($$\Delta S) $$when ice melts at 0$$^\circC$$?

Accepted Answer

$$\Delta S is $$positive because the system becomes more disordered.

Question 3

Given the following reaction at 25$$^\circC$$: $$\ce{2H2(g) + O2(g) -\u003e 2H2O(l)}$$, with $$\Delta H^\circ = -571.6\ \mathrm{kJ}$$ and $$\Delta S^\circ = -327\ \mathrm{J/K}$$, calculate $$\Delta G^\circ$$ for the reaction.

Accepted Answer

$$\Delta G^\circ = -474.5\ \mathrm{kJ}$$

Question 4

Which of the following processes results in a decrease in entropy ($$\Delta S \u003c 0$$)?

Accepted Answer

Condensation of steam ($$\ce{H2O(g) -\u003e H2O(l)})$$

Question 5

A reaction has $$\Delta H = +100\ \mathrm{kJ}$$ and $$\Delta S = +200\ \mathrm{J/K}. At $$what temperature does the reaction become spontaneous?

Accepted Answer

At $$T \u003e 500\ \mathrm{K}$$

Question 6

Which of the following is the correct cell notation for a galvanic cell based on the reaction: $$\ce{Zn(s) + Cu$$^{2+}$$(aq) -\u003e Zn$$^{2+}$$(aq) + Cu(s)}$$?

Accepted Answer

$$\ce{Zn(s) | Zn$$^{2+}$$(aq) || Cu$$^{2+}$$(aq) | Cu(s)}$$

Question 7

Given the standard reduction potentials: $$E^\circ(\ce{Ag^+/Ag}) = +0.80\ \mathrm{V}$$ and $$E^\circ(\ce{Cu$$^{2+}$$/Cu}) = +0.34\ \mathrm{V}$$, which metal will be reduced in a galvanic cell constructed from these half-cells?

Accepted Answer

Silver, because it has a higher reduction potential.

Question 8

Which of the following statements about the equilibrium constant $$K$$ and $$\Delta G^\circ is $$correct?

Accepted Answer

If $$K = 1$$, then $$\Delta G^\circ = 0.$$

Question 9

A voltaic cell is constructed using the following half-reactions:

$$\ce{Fe$$^{2+}$$ + 2e^- -\u003e Fe(s)}$$ $$E^\circ = -0.44\ \mathrm{V}$$
$$\ce{Cu$$^{2+}$$ + 2e^- -\u003e Cu(s)}$$ $$E^\circ = +0.34\ \mathrm{V}$$

What is the standard cell potential ($$E^\circ_{cell}$$)?

Accepted Answer

$$E^\circ_{cell} = +0.78\ \mathrm{V}$$

Question 10

Which of the following best describes the role of the salt bridge in a galvanic cell?

Accepted Answer

It completes the circuit by allowing ion flow.

Question 11

Which of the following is the correct balanced nuclear equation for the beta decay of $$\ce{^{14}C}$$?

Accepted Answer

$$\ce{^{14}C -\u003e$$ ^{14}$$N + e^-}$$

Question 12

Which of the following organic compounds contains a carboxylic acid functional group?

Accepted Answer

$$\ce{CH3COOH}$$

Question 13

Which of the following statements is true regarding the spontaneity of a reaction with $$\Delta H \u003c 0$$ and $$\Delta S \u003c 0$$?

Accepted Answer

The reaction is spontaneous only at low temperatures.

Question 14

Which of the following is the correct definition of an oxidizing agent?

Accepted Answer

A substance that gains electrons and is reduced.

Question 15

Given the following reaction: $$\ce{2Al(s) + 3Cu$$^{2+}$$(aq) -\u003e 2Al$$^{3+}$$(aq) + 3Cu(s)}$$, which species is oxidized?

Accepted Answer

$$\ce{Al(s)}$$

Question 16

Which of the following best describes the change in atomic number and mass number during alpha decay?

Accepted Answer

Atomic number decreases by 2, mass number decreases by 4.

Question 17

Which of the following is the correct formula for calculating the standard free energy change from the equilibrium constant?

Accepted Answer

$$\Delta G^\circ = -RT \ln K$$

Question 18

Which of the following is the correct balanced equation for the combustion of ethanol ($$\ce{C2H5OH}$$)?

Accepted Answer

$$\ce{C2H5OH + 3O2 -\u003e 2CO2 + 3H2O}$$

Question 19

Which of the following best describes the function of a catalyst in a chemical reaction?

Accepted Answer

It lowers the activation energy.

Question 20

Which of the following is the correct formula for calculating the cell potential under nonstandard conditions?

Accepted Answer

$$E = E^\circ - \frac{0.0592}{n} \log Q$$

Exam III Review: Thermodynamics, Electrochemistry, Nuclear Chemistry, and Organic Chemistry

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