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AP Chemistry Unit 7: Equilibrium

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Unit 7: Equilibrium

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Question 1

For the dissolution of calcium fluoride, $Ca F_{2} (s) ⇌ C a^{2 +} (aq) + 2 F^{-} (aq)$ , the $K_{s p} = 3.9 \times 1 0^{- 11}$ . What is the molar solubility of $Ca F_{2}$ ?

2.1 \times 1 0^{- 4} M

3.9 \times 1 0^{- 11} M

6.2 \times 1 0^{- 6} M

1.3 \times 1 0^{- 4} M

Question 2

For the equilibrium $N_{2} (g) + 3 H_{2} (g) ⇌ 2 N H_{3} (g)$ , which expression correctly represents $K_{c}$ ?

K_{c} = \frac{[ N H _{3} ] ^{2}}{[ N _{2} ] [ H _{2} ] ^{3}}

K_{c} = \frac{[ N _{2} ] [ H _{2} ] ^{3}}{[ N H _{3} ] ^{2}}

K_{c} = \frac{[ N H _{3} ]}{[ N _{2} ] [ H _{2} ]}

K_{c} = \frac{[ N H _{3} ] ^{2}}{[ N _{2} ] ^{2} [ H _{2} ] ^{3}}

Question 3

At equilibrium, increasing the pressure on a gas-phase reaction by reducing volume will shift the equilibrium in the direction that:

A.Decreases the total number of moles of gas.B.Increases the total number of moles of gas.C.Has no effect, since gases are compressible.D.Increases temperature.

Question 4

The common-ion effect predicts that the molar solubility of AgCl ( $K_{s p} = 1.8 \times 1 0^{- 10}$ ) in a $0.10 M$ NaCl solution is:

A.Greater than

1.3 \times 1 0^{- 5} M

1.3 \times 1 0^{- 5} M

(unchanged)C.

1.8 \times 1 0^{- 9} M

1.8 \times 1 0^{- 10} M

Question 5

According to Le Châtelier's principle, what happens to the equilibrium position of $N_{2} (g) + 3 H_{2} (g) ⇌ 2 N H_{3} (g)$ ( $Δ H = - 92 kJ$ ) when the temperature is increased?

A.Shifts forward; more NH

_{3}

is produced.B.Shifts reverse;

K_{c}

decreases.C.No effect; temperature does not affect

K_{c}

.D.Shifts forward;

K_{c}

increases.

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Question 6

The solubility product of silver chloride is $K_{s p} (AgCl) = 1.8 \times 1 0^{- 10}$ at $25° C$ . What is the molar solubility (in mol/L) of AgCl in pure water?

1.8 \times 1 0^{- 10} M

1.3 \times 1 0^{- 5} M

9.0 \times 1 0^{- 21} M

3.6 \times 1 0^{- 10} M

Question 7

Adding an inert gas to a gaseous equilibrium system at constant volume has what effect on the equilibrium position?

A.Shifts toward the side with more moles of gas.B.Shifts toward the side with fewer moles of gas.C.No shift; the equilibrium position is unchanged.D.Shifts forward to consume the extra pressure.

Question 8

For a reaction with $K_{c} = 5.0 \times 1 0^{- 8}$ , which statement best characterizes the equilibrium?

A.At equilibrium, the mixture contains mostly products.B.At equilibrium, reactants and products are present in roughly equal amounts.C.At equilibrium, the mixture is predominantly reactants.D.The reaction does not reach equilibrium because

K_{c}

is too small.

Question 9

The relationship between $K_{c}$ and $K_{p}$ for a gas-phase equilibrium is $K_{p} = K_{c} (R T)^{Δ n}$ , where $Δ n$ is the change in moles of gas. For the reaction $2 S O_{3} (g) ⇌ 2 S O_{2} (g) + O_{2} (g)$ , $Δ n =$ ?

- 1

+ 1

+ 2

0

Question 10

For the equilibrium $A (g) ⇌ 2 B (g)$ , an ICE table gives the following initial and change rows:

	A	B
Initial	$0.600 M$	$0$
Change	$- x$	$+ 2 x$
Equilibrium	$0.600 - x$	$2 x$

If $K_{c} = 0.040$ , what is the equilibrium concentration of A?

0.550 M

0.600 M

0.200 M

0.0500 M

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Question 11

For the reaction $PC l_{5} (g) ⇌ PC l_{3} (g) + C l_{2} (g)$ , $K_{c} = 1.8 \times 1 0^{- 2}$ at a certain temperature. If a reaction mixture has $[PC l_{5}] = 0.50 M$ , $[PC l_{3}] = 0.15 M$ , and $[C l_{2}] = 0.15 M$ , in which direction will the reaction proceed?

A.Forward, toward products, because

Q < K_{c}

.B.Reverse, toward reactants, because

Q > K_{c}

.C.Neither; the system is at equilibrium because all concentrations are nonzero.D.Forward, because the products have lower concentrations than the reactant.

Question 12

Removing a product from a reaction system at equilibrium will:

A.Shift the equilibrium to the left (toward reactants) to replenish what was removed.B.Shift the equilibrium to the right (toward products) to partially restore the product concentration.C.Have no effect because

K_{c}

does not change.D.Decrease

K_{c}

to account for the lower product concentration.

AP Chemistry Unit 7: Equilibrium — Free with Answer Explanations | Test Practice Hub