Q: A reaction is first order in A. If the initial concentration of A is 0.50 M and the rate constant $$k is$$ $$0.10\ \text{min}^{-1}$$, what is the half-life of A?

$$t_{1/2} = \frac{0.693}{0.10} = 6.93\ \text{min}$$

Q: A buffer solution is made by mixing 0.20 mol of acetic acid ($$\text{p}K_a = 4.76) $$and 0.10 mol of sodium acetate in 1.0 L of water. What is the pH of the solution?

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

Q: A solution is prepared by dissolving 0.5 mol of NaCl in 1.0 kg of water. What is the molality of the solution?

$$m = \frac{0.5}{1.0} = 0.5\ \text{mol/kg}$$

Q: Which equation would you use to calculate the percent ionization of a weak acid?

$$\text{Percent Ionization} = \frac{[H^+]}{[HA]_{initial}} \times 100\%$$

Question 1

A sample of gas is collected over water at 25°C. The total pressure is 760 mmHg, and the vapor pressure of water at this temperature is 24 mmHg. What is the partial pressure of the dry gas?

Accepted Answer

$$P_{gas} = 736\ 	ext{mmHg}$$

Question 2

Which equation would you use to calculate the boiling point elevation of a solution, and what variable represents the molality?

Accepted Answer

$$\Delta T_b = i K_b m$$; $$m is $$molality

Question 3

A reaction is first order in A. If the initial concentration of A is 0.50 M and the rate constant $$k is$$ $$0.10\ 	ext{min}^{-1}$$, what is the half-life of A?

Accepted Answer

$$t_{1/2} = \frac{0.693}{0.10} = 6.93\ 	ext{min}$$

Question 4

Which of the following correctly expresses the relationship between Gibbs free energy and the equilibrium constant?

Accepted Answer

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

Question 5

A buffer solution is made by mixing 0.20 mol of acetic acid ($$	ext{p}K_a = 4.76) $$and 0.10 mol of sodium acetate in 1.0 L of water. What is the pH of the solution?

Accepted Answer

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

Question 6

Which equation would you use to determine the entropy change of the universe for a spontaneous process at constant temperature?

Accepted Answer

$$\Delta S_{univ} = \Delta S_{sys} + \Delta S_{surr}$$

Question 7

A solution is prepared by dissolving 0.5 mol of NaCl in 1.0 kg of water. What is the molality of the solution?

Accepted Answer

$$m = \frac{0.5}{1.0} = 0.5\ 	ext{mol/kg}$$

Question 8

Which of the following is the correct form of the Arrhenius equation in its linear form?

Accepted Answer

$$\ln k = -\frac{E_a}{R} \left( \frac{1}{T} \right) + \ln A$$

Question 9

If the equilibrium constant $$K_c$$ for a reaction is $$1.0 	imes 10^5$, what does this indicate about the position of equilibrium?

Accepted Answer

The equilibrium favors the products.

Question 10

Which equation would you use to calculate the percent ionization of a weak acid?

Accepted Answer

$$	ext{Percent Ionization} = \frac{[H^+]}{[HA]_{initial}} 	imes 100\%$$

Question 11

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

Accepted Answer

$$T \u003e 500\ 	ext{K}$$

Question 12

Which equation relates the cell potential to the Gibbs free energy change?

Accepted Answer

$$\Delta G^\circ = -n F E^\circ_{cell}$$

Question 13

Which of the following is the correct expression for the acid dissociation constant $$K_a$$?

Accepted Answer

$$K_a = \frac{[H^+][A^-]}{[HA]}$$

Question 14

A solution has a pH of 3. What is the concentration of $$H^+$$ ions in the solution?

Accepted Answer

$$[H^+] = 1 	imes 10$$^{-3}$$\ 	ext{M}$$

Question 15

Which equation would you use to calculate the freezing point depression of a solution?

Accepted Answer

$$\Delta T_f = i K_f m$$

Question 16

Which equation describes the relationship between the rate constant and temperature according to the Arrhenius equation?

Accepted Answer

$$k = A e$$^{-E_a / RT}$$

Question 17

Which equation would you use to calculate the osmotic pressure of a solution?

Accepted Answer

$$\Pi = i M R T$$

Question 18

Which equation would you use to relate the equilibrium constants $$K_p$$ and $$K_c$$ for a reaction involving gases?

Accepted Answer

$$K_p = K_c (RT$$)^{\Delta n}$$

General Chemistry II: Essential Equations and Concepts Study Guide

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