Q: Calculate the entropy change ($$\Delta S) $$for the vaporization of 1 mol of water at 100°C, given $$\Delta H_{vap} = 40.7 kJ/$$mol and $$T = 373 K.$$

$$\Delta S = \dfrac{40.7 \times 10^3$}{373} = 109 J/K$$

Question 1

Which of the following changes would result in an increase in entropy ($$\Delta S \u003e 0) $$for a chemical system?

Accepted Answer

Dissolving NaCl in water

Question 2

Calculate the entropy change ($$\Delta S) $$for the vaporization of 1 mol of water at 100°C, given $$\Delta H_{vap} = 40.7 kJ/$$mol and $$T = 373 K.$$

Accepted Answer

$$\Delta S = \dfrac{40.7 	imes 10^3$}{373} = 109 J/K$$

Question 3

A reaction has $$\Delta H = -125 kJ $$and $$\Delta S = -200 J/K. At $$what temperature will the reaction become nonspontaneous?

Accepted Answer

$$T \u003e \dfrac{\Delta H}{\Delta S} = \dfrac{-125,000}{-200} = 625 K$$

Question 4

Which equation correctly relates Gibbs free energy to enthalpy and entropy?

Accepted Answer

$$\Delta G = \Delta H - T\Delta S$$

Question 5

Given the following reactions and their $$\Delta G^\circ$$ values:

1. $$A \rightarrow B$$, $$\Delta G^\circ = -50 kJ
2$$. $$B \rightarrow C$$, $$\Delta G^\circ = +30 kJ

$$What is $$\Delta G^\circ$$ for $$A \rightarrow C$$?

Accepted Answer

$$\Delta G^\circ = -20 kJ$$

Question 6

Which of the following statements about standard cell potential ($$E^\circ_{cell}) is $$correct?

Accepted Answer

$$E^\circ_{cell} = E^\circ_{cathode} - E^\circ_{anode}$$

Question 7

A voltaic cell is constructed using a Zn/Zn$$^{2+}$$ half-cell and a Cu/Cu$$^{2+}$$ half-cell. Given $$E^\circ_{Zn$$^{2+}$$/Zn} = -0.76 V $$and $$E^\circ_{Cu$$^{2+}$$/Cu} = +0.34 V$$, what is the standard cell potential?

Accepted Answer

$$E^\circ_{cell} = 0.34 - (-0.76) = 1.10 V$$

Question 8

Which of the following correctly describes the process of balancing a redox reaction in acidic solution?

Accepted Answer

Balance all elements except H and O, then balance O with H$$_2O$$, H with H$$^+$$, and electrons last.

Question 9

For the reaction $$2Fe^{3+} + 2I$$^- \rightarrow $$2Fe^{2+}$$ + $$I_2$$, which species is oxidized?

Accepted Answer

I$$^-$$

Question 10

Using the Nernst equation, calculate the cell potential at 25°C for a cell with $$E^\circ_{cell} = 1.10 V $$and $$Q = 10$$.

$$E_{cell} = E^\circ_{cell} - \dfrac{0.0592}{n} \log Q$$, where $$n = 2.$$

Accepted Answer

$$E_{cell} = 1.10 - \dfrac{0.0592}{2} \log 10 = 1.10 - 0.0296 = 1.070 V$$

Question 11

Which of the following is true about alpha decay?

Accepted Answer

The nucleus emits a $$^4_2He$$ particle, decreasing its mass number by 4 and atomic number by 2.

Question 12

Which equation is used to calculate the binding energy from mass defect?

Accepted Answer

$$E = \Delta m c^2$

Question 13

A radioactive isotope has a half-life of 10 years. How much of a 100 g sample remains after 30 years?

Accepted Answer

12.5 g

Question 14

Which of the following is a correct statement about beta decay?

Accepted Answer

A neutron is converted to a proton, and a $$^0_{-1}e$$ particle is emitted.

Question 15

Which process is used in radiocarbon dating to determine the age of ancient artifacts?

Accepted Answer

Comparing the ratio of $$^{14}C to$$ $$^{12}C in $$the sample

Question 16

Which of the following is true about the spontaneity of a reaction at standard conditions?

Accepted Answer

If $$\Delta G^\circ \u003c 0$$, the reaction is spontaneous.

Question 17

Which of the following is the correct formula for calculating the standard entropy change ($$\Delta S^\circ) of a $$reaction?

Accepted Answer

$$\Delta S^\circ = \sum S^\circ_{products} - \sum S^\circ_{reactants}$$

Question 18

Which of the following is a correct application of Faraday's law in the stoichiometry of electrolytic cells?

Accepted Answer

The amount of substance produced is proportional to the total charge passed: $$n = \dfrac{Q}{Fz}$$

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