Question 1

Why are pure solids and pure liquids omitted from the mathematical expression for an equilibrium constant ($$K_c$$)?

Accepted Answer

Their density, and consequently their molar concentration, remains constant throughout the reaction.

Question 2

Given the following equilibrium data at a certain temperature:
(1) $$A_2(g$$) + $$B_2(g$$) \rightleftharpoons 2AB(g)$$, K$$_{c1} = 0.01$$
(2) 2AB(g$$) + $$B_2(g$$) \rightleftharpoons 2AB_2(g)$$, K$$_{c2} = 100$$
What is the equilibrium constant for the reaction 2AB_2(g$$) \rightleftharpoons $$A_2(g) + 2B_2(g$$)$$ at the same temperature?

Accepted Answer

$$0.0001$$

Question 3

Consider the following system in a $$1.00 L $$container: $$R(g) + S(g) \rightleftharpoons 2T(g). $$The initial equilibrium concentrations at a certain temperature are: $$[R(g)] = 4.0 M$$, $$[S(g)] = 1.0 M$$, and $$[T(g)] = 4.0 M. $$How many moles of $$S(g)$$ must be added to increase the concentration of $$T(g) to$$ $$6.0 M at $$this same temperature?

Accepted Answer

2.5 moles

Question 4

Each reaction is allowed to come to equilibrium, and then the temperature is changed as indicated. Predict the effect of the indicated temperature change.
(a) $$I_2(g$$) \rightleftharpoons 2I(g)$$, $$\Delta H \u003e 0$$, increased
(b) 2H_2S(g$$) \rightleftharpoons 2H_2(g) + $$S_2(g$$)$$, $$\Delta H \u003e 0$$, decreased
(c) I_2$(g) + Cl_2$(g) \rightleftharpoons 2ICl(g)$$, $$\Delta H \u003c 0$$, decreased

Accepted Answer

shifts left, shifts right, shifts left

Question 5

Consider the equilibrium: $$K(g) + L(g) \rightleftharpoons M(g) + N(g). $$Starting with only $$50.0$$ torr of gaseous $$K$$ and $$50.0$$ torr of gaseous $$L$$, an equilibrium is established that leaves only $$20.0$$ torr of $$K(g) at $$equilibrium. What is the equilibrium constant, $$K_p$$?

Accepted Answer

$$2.25$$

Question 6

Consider ionization of a weak base $$B$$:
$$B(aq) + H_2O(\ell) \rightleftharpoons BH^+(aq) + OH^-(aq)$$
The pH of the solution at $$25^\circC is$$ $$10.50. $$Temperature is raised to $$30^\circC $$and new equilibrium is established with a new pH of $$9.00. $$Which of the following is correct about this reaction?

Accepted Answer

It shifts to left when temperature increases

Question 7

A $$0.005 M $$base solution that yields one equivalent of hydroxide ($$OH^-) $$ions per formula unit has a pH of $$11.00 at$$ $$25^\circC. $$Which of the following is correct about this base?

Accepted Answer

Its conjugate acid will react with water to produce an acidic solution.

Question 8

What is the pH of a solution that is $$1.15\%$$ $$Ba(OH)_2 by $$mass at $$25^\circC$$? (Assume that the solution has density of $$1.01 g/mL.)$$

Accepted Answer

$$13.13$$

Question 9

Which one of the following will form a basic solution in water?

Accepted Answer

NaCHO$$_2$$

Question 10

Consider the following solutions: $$Al(NO_3$)_3$$, $$HCl$$, $$KCl$$, $$LiCN. $$Arrange the solutions given above in order of increasing acidity, from the least acidic to the most acidic.

Accepted Answer

$$LiCN \u003c KCl \u003c Al(NO_3$)_3 \u003c HCl$$

Question 11

A laboratory technician needs to prepare $$7.50 L of an $$aqueous $$HClO_4$$ solution with a pH of $$2.74. $$The only source available is a concentrated stock solution of $$HClO_4$$ that is $$70\% by $$mass and has a density of $$1.67 g/mL. $$What volume of this stock solution must be measured out?

Accepted Answer

$$15.1 mL$$

Question 12

Calculate the pH and pOH of a $$0.50 M$$ $$NaCHO_2$$ solution. ($$K_a$$ for $$HCHO_2 is$$ $$1.8 	imes 10$$^{-4}$$)

Accepted Answer

pH = $$8.87$$, pOH = $$5.13$$

Question 13

Consider the equilibrium $$2P(g) + Q(g) \rightleftharpoons R(g) + \frac{1}{4}S(g). An $$initial mixture contains $$[P] = 25.0 M$$, $$[Q] = 14.0 M$$, and $$[S] = 13.0 M. At $$equilibrium, $$[R] = 12.0 M. $$What is the value of $$K_c$$?

Accepted Answer

$$K_c = 0.024$$

Question 14

Which of the following changes will increase the value of the equilibrium constant $$K_c$$ for an exothermic reaction?

Accepted Answer

Decreasing the temperature

Question 15

A student mixes $$0.10$$ mol $$NH_3$$ and $$0.10$$ mol $$HCl in$$ $$1.0 L of $$water. Which statement best describes the resulting solution?

Accepted Answer

The solution will be slightly acidic due to the formation of $$NH_4$$^+$$.

Question 16

Which of the following salts will produce a solution with pH less than 7 when dissolved in water?

Accepted Answer

NH_4Cl

Question 17

Which of the following statements about Le Chatelier's Principle is correct?

Accepted Answer

Removing a reactant will shift the equilibrium to the left.

Question 18

A solution is prepared by dissolving $$0.10$$ mol $$NaF in$$ $$1.0 L of $$water. What is the pH of the solution? ($$K_a$$ for $$HF is$$ $$6.8 	imes 10$$^{-4}$$)

Accepted Answer

pH = $$8.08$$

General Chemistry Practice Exam 2 – Step-by-Step Study Guidance

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