Q: A sample of gas occupies 10.0 L at 2.00 atm and 300 K. If the pressure is increased to 4.00 atm and the temperature is decreased to 150 K, what will be the new volume of the gas, assuming ideal behavior?

$$V_2$$ = $$V_1$$ \times \frac{$$P_1$$}{$$P_2$$} \times \frac{$$T_2$$}{$$T_1$$} = 10.0\,\text{L} \times \frac{2.00}{4.00} \times \frac{150}{300} = 2.5\,\text{L}$$

Q: A reaction has $$\Delta H = -100\,\text{kJ}$$ and $$\Delta S = -200\,\text{J/K}. At $$what temperature does the reaction change from spontaneous to nonspontaneous?

$$T = \frac{\Delta H}{\Delta S} = \frac{-100,000\,\text{J}}{-200\,\text{J/K}} = 500\,\text{K}$$

Q: A voltaic cell is constructed using the following half-reactions: $$\text{Zn}^{2+} + 2e^- \rightarrow \text{Zn}$$ ($$E^\circ = -0.76\,\text{V}) $$and $$\text{Cu}^{2+} + 2e^- \rightarrow \text{Cu}$$ ($$E^\circ = +0.34\,\text{V}). $$What is the standard cell potential?

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

Q: A buffer is prepared by mixing 0.20 mol of acetic acid ($$\text{CH}_3\text{COOH}) $$and 0.10 mol of sodium acetate ($$\text{CH}_3\text{COONa}) in $$enough water to make 1.0 L of solution. If $$pK_a = 4.76$$, what is the pH of the buffer?

$$\text{pH} = 4.76 + \log \left( \frac{0.10}{0.20} \right) = 4.76 + \log(0.5) = 4.46$$

Question 1

A sample of gas occupies 10.0 L at 2.00 atm and 300 K. If the pressure is increased to 4.00 atm and the temperature is decreased to 150 K, what will be the new volume of the gas, assuming ideal behavior?

Accepted Answer

$$V_2$$ = $$V_1$$ 	imes \frac{$$P_1$$}{$$P_2$$} 	imes \frac{$$T_2$$}{$$T_1$$} = 10.0\,	ext{L} 	imes \frac{2.00}{4.00} 	imes \frac{150}{300} = 2.5\,	ext{L}$$

Question 2

Which of the following statements best explains why water has a higher boiling point than methane?

Accepted Answer

Water forms hydrogen bonds, which are stronger than the London dispersion forces present in methane.

Question 3

A reaction has $$\Delta H = -100\,	ext{kJ}$$ and $$\Delta S = -200\,	ext{J/K}. At $$what temperature does the reaction change from spontaneous to nonspontaneous?

Accepted Answer

$$T = \frac{\Delta H}{\Delta S} = \frac{-100,000\,	ext{J}}{-200\,	ext{J/K}} = 500\,	ext{K}$$

Question 4

Which of the following alloys is best described as a homogeneous mixture of metals with atoms of similar size?

Accepted Answer

Substitutional alloy

Question 5

A face-centered cubic (FCC) unit cell contains how many atoms per unit cell?

Accepted Answer

4

Question 6

Which of the following best describes the effect of increasing temperature on the rate constant $$k$$ for a reaction, according to the Arrhenius equation?

Accepted Answer

$$k$$ increases exponentially with temperature.

Question 7

A voltaic cell is constructed using the following half-reactions: $$	ext{Zn}^{2+} + 2e^- ightarrow 	ext{Zn}$$ ($$E^\circ = -0.76\,	ext{V}) $$and $$	ext{Cu}^{2+} + 2e^- ightarrow 	ext{Cu}$$ ($$E^\circ = +0.34\,	ext{V}). $$What is the standard cell potential?

Accepted Answer

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

Question 8

Which of the following statements about n-type and p-type semiconductors is correct?

Accepted Answer

n-type semiconductors are doped with elements that have more valence electrons than the host, while p-type are doped with elements with fewer valence electrons.

Question 9

A buffer is prepared by mixing 0.20 mol of acetic acid ($$	ext{CH}_3	ext{COOH}) $$and 0.10 mol of sodium acetate ($$	ext{CH}_3	ext{COONa}) in $$enough water to make 1.0 L of solution. If $$pK_a = 4.76$$, what is the pH of the buffer?

Accepted Answer

$$	ext{pH} = 4.76 + \log \left( \frac{0.10}{0.20} ight) = 4.76 + \log(0.5) = 4.46$$

Question 10

Which of the following changes will shift the equilibrium of the reaction $$	ext{N}_2(g) + 3	ext{H}_2(g) ightleftharpoons 2	ext{NH}_3(g) to $$the right, according to Le Chatelier’s principle?

Accepted Answer

Increasing the pressure by decreasing the volume.

Question 11

Which of the following is the correct expression for the equilibrium constant $$K_p in $$terms of $$K_c$$ for the reaction $$2	ext{SO}_2(g) + 	ext{O}_2(g) ightleftharpoons 2	ext{SO}_3(g)$$?

Accepted Answer

$$K_p = K_c(RT$$)^{\Delta n}$$, where $$\Delta n = (2) - (2+1) = -1$$

Question 12

Which of the following best describes the process occurring when ice melts at 0°C and 1 atm?

Accepted Answer

The process is endothermic and $$\Delta S is $$positive.

Question 13

Which of the following is a correct statement about the relationship between $$Q$$, $$K$$, and $$\Delta G$$ for a chemical reaction?

Accepted Answer

If $$Q \u003c K$$, then $$\Delta G \u003c 0$$ and the reaction proceeds forward.

Question 14

Which of the following is the correct formula for calculating the energy change when a system does work on the surroundings and absorbs heat?

Accepted Answer

$$\Delta E = q + w$$

Question 15

Which of the following is the correct formula for the rate constant $$k$$ for a first-order reaction?

Accepted Answer

$$k = \frac{1}{t} \ln \frac{[A]_0}{[A]}$$

Question 16

Which of the following best describes the color change of a solution containing a weak acid and its conjugate base when a few drops of strong base are added?

Accepted Answer

The color changes slightly, as the buffer resists large pH changes.

Question 17

Which of the following is the correct formula for calculating the standard free energy change from the standard cell potential?

Accepted Answer

$$\Delta G^\circ = -nFE^\circ$$

Question 18

Which of the following is a correct statement about the entropy change ($$\Delta S) $$for the reaction $$2	ext{H}_2(g) + 	ext{O}_2(g) ightarrow 2	ext{H}_2	ext{O}(l)$$?

Accepted Answer

$$\Delta S is $$negative because the number of moles of gas decreases.

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