Deck 18: Chemical Equilibrium

Question 1

Which of the following is the best description of the activation energy for the forward reaction for the reaction A₂ + B₂ 2 AB?

A)The difference between the energy of the activated complex and the reactant energies
B)The difference between the product energies and the energy of the activated complex
C)The difference between the product energies and the reactant energies
D)The sum of the energy of the activated complex and the reactant energies
E)The sum of the energy of the activated complex and the product energies

Answer 1

The difference between the energy of the activated complex and the reactant energies

Question 2

Which of the following statements does not correctly describe the character of a chemical equilibrium?

A)As a system comes to equilibrium,the chemical reactions come to a stop
B)In a liquid-gas equilibrium,the number of moles of the gas does not necessarily equal the number of moles of the liquid
C)In a solution equilibrium,the number of moles of the solvent does not necessarily equal the number of moles of the liquid
D)All of the statements above correctly describe a chemical equilibrium
E)None of the statements above correctly describes a chemical equilibrium

Answer 2

As a system comes to equilibrium,the chemical reactions come to a stop

Question 3

Which of the following statements is/are incorrect?
(i)Undissolved sugar in contact with a saturated sugar solution in an open beaker cannot reach equilibrium
(ii)A liquid and its vapor enclosed in two one-liter containers connected by an open glass tube cannot reach equilibrium
(iii)A solution of a weak acid,hydronium ion,and the conjugate base of the weak acid cannot reach equilibrium

A)i only
B)ii only
C)i and ii
D)ii and iii
E)i,ii,and iii

Answer 3

i,ii,and iii

Question 4

Which of the following statements is incorrect?
(i)The collision theory of chemical reactions states that what we see as a chemical reaction is the overall effect of a high number of individual collisions between reacting particles
(ii)A violent,bond-breaking collision is most apt to occur if the colliding molecules are moving at high speed
(iii)Most collisions do not result in a reaction

A)iii only
B)i and iii
C)ii and iii
D)All statements are correct
E)All statements are incorrect

Question 5

If a reaction is carried out in an aqueous solution,which of the following changes would not affect the rate of the reaction?

A)Increasing the temperature
B)Changing the concentration of reactants
C)Increasing the size of the reaction vessel
D)Adding a catalyst
E)More than one would not affect the rate of the reaction

Question 6

How does a catalyst alter the rate of a reaction?

A)Catalysts replace part of the reactants
B)Catalysts provide the activation energy needed
C)A catalyst interferes with the attainment of chemical equilibrium
D)Catalysts provide more heat to the reaction,and the increased temperature leads to an increased reaction rate
E)Catalysts provide a reaction pathway with a lower energy of activation

Question 7

How will the rate of reaction change if the concentration of reactants is decreased?

A)The rate will increase
B)The rate will decrease
C)Products will form more rapidly,so there will be no change in the rate
D)The rate of product formation will increase
E)A change in concentration leads to an unpredictable effect on the rate of reaction

Question 8

How does increasing the temperature increase the rate of a chemical reaction?

A)The fraction of sample with the minimum kinetic energy required to react is increased
B)The activation energy for the reaction is decreased
C)The bond energy of the reactants is decreased
D)The likelihood that molecules and ions will have the required geometry is increased
E)The electrons become more reactive because they spin on their own axes at a higher rate

Question 9

Which of the following conditions is not found in a system that is at equilibrium?

A)Reactants and products are being converted into one another continually
B)The forward rate of reaction is equal to the rate of the reverse reaction
C)The concentration of reactants is equal to the concentration of the products
D)The system is closed and isolated from its surroundings
E)The reaction can be represented by an equation with a double arrow

Question 10

Consider the following reaction coordinate diagram. Based on this diagram,which of the following is correct?

A)2 represents $\Delta$ E and the reaction is exothermic.
B)2 represents $\Delta$ E and the reaction is endothermic
C)3 represents $\Delta$ E and the reaction is endothermic
D)3 represents $\Delta$ E and the reaction is exothermic
E)5 represents $\Delta$ E and the reaction is exothermic

Question 11

A molecular collision is sufficiently energetic to cause a reaction,yet no reaction occurs.Which of the following is the least likely explanation?

A)The proton-proton interaction is too large
B)The molecules have poor orientation
C)One of the molecules is not moving too slowly.
D)One or both the molecules does not have enough energy.
E)All of the above could be an explanation.

Question 12

Consider the diagram given below. Which number point on the diagram indicates the E_a for the forward reaction?

A)1
B)2
C)3
D)4
E)5

Question 13

Consider the hypothetical reaction A + 2 B AB₂ at equilibrium.Which is true?

A)The reverse reaction rate is at a maximum
B)The concentration of A must equal the concentration of B
C)The concentration of A must equal one-half the concentration of B
D)The forward reaction rate is equal to the reverse reaction rate
E)The forward reaction rate is equal to the equilibrium reaction rate

Question 14

Consider the following reaction coordinate diagram. Which numbered point represents the transition state of the reaction?

A)1
B)2
C)3
D)4
E)5

Question 15

Which of the following statements is/are correct?
(i)An object hanging motionless on a spring is in a static equilibrium
(ii)In a dynamic equilibrium,the reversible changes occur continuously,even though there is no appearance of change
(iii)The amounts of substances present in a system at equilibrium are equal

A)i only
B)ii only
C)iii only
D)i and ii
E)ii and iii

Question 16

Which of the following is the primary reason for a higher reaction rate at higher temperatures?

A)Molecules move faster at higher temperatures,producing more violent collisions
B)Electrons occupy higher principal energy levels and are therefore more reactive
C)There is a larger fraction of molecules with sufficient energy to react
D)Molecules increase in size with increasing temperature,providing more surface area for potential collisions
E)The higher temperature creates a lower activation energy,so more molecules can pass over the potential energy barrier

Question 17

Which of the following statements are incorrect?
(i)When opposing reversible reactions occur at different rates,the faster reaction gradually becomes slower.
(ii)Equilibrium is established when forward and reverse reaction rates become equal
(iii)In the development of a chemical equilibrium,the reverse reaction rate decreases over time until equilibrium is established

A)iii only
B)i and ii
C)i and iii
D)ii and iii
E)i,ii,and iii

Question 18

Consider the particulate level representation of a reaction of the form:
Based on just this diagram,which of the following does not correctly describes this reaction?

A)The collision was ineffective.
B)Product did not form.
C)The orientation of the reactants to with respect to each other was wrong.
D)The molecules had too much potential energy.
E)All of the above do describe this reaction.

Question 19

What kind of molecular collisions will not lead to the formation of product in a reaction?

A)Only those without sufficient kinetic energy
B)Only those with the wrong orientation,regardless of the kinetic energy
C)Collisions between molecules that have more energy than the minimum required
D)Those without sufficient kinetic energy and with the wrong orientation
E)Those with effective collisions

Question 20

Consider the following reaction coordinate diagram. The energy value corresponding to which point(s)will change if a catalyst is added to this reaction?

A)1 and 5
B)1,3,and 5
C)2,3,and 4
D)2 and 4
E)All will change their energy value.

Question 21

Which of the following statements is/are correct?
(i)The forward reaction in an equilibrium reaction is exactly the reverse of the reverse reaction
(ii)A dynamic equilibrium is established when two molecules collide
(iii)As reactant concentrations in a chemical equilibrium reaction decrease,the forward reaction rate declines

A)ii only
B)i and ii
C)i and iii
D)ii and iii
E)i,ii,and iii

Question 22

If a copper(II)nitrate solution is added to a sodium sulfide solution the following equilibrium will be attained: Cu²⁺(aq)+ S^2-(aq) CuS(s).For this equilibrium,K = 6.3*10⁴⁷.Choose the correct equilibrium constant expression and the correct direction favored at equilibrium.

A)K = forward
B)K = reverse
C)K = forward
D)K = reverse
E)K = appreciable quantities of all species are present at equilibrium

Question 23

What will happen if the temperature is decreased after equilibrium has been established in the reaction below? 2 C₂H₆(g)+ 7 O₂(g) 4 CO₂(g)+ 6 H₂O(g)+ 2855 kJ

A)There will be no change in the system
B)The concentration of ethane will increase
C)The partial pressure of oxygen will increase
D)The number of water molecules will decrease
E)More carbon dioxide will form

Question 24

What will happen if the temperature is increased after equilibrium has been established in the reaction shown? 2 Cl₂(g)+ 2 H₂O(g)+ 113 kJ 4 HCl(g)+ O₂(g)

A)The position of equilibrium shifts to the left
B)More HCl will form
C)More Cl₂ will form
D)The partial pressure of oxygen will decrease
E)The concentration of H₂O will increase

Question 25

K = 1.3 * 10^-10 for the reaction HC₆H₅O(aq) H⁺(aq)+ C₆H₅O^-(aq).In which direction is the equilibrium favored?

A)Forward
B)Reverse
C)Appreciable quantities of all species are present at equilibrium
D)No direction is favored
E)There is not enough information to determine the direction

Question 26

Which of the following statements is/are correct?
(i)If an equilibrium constant is very large,the reverse reaction is favored
(ii)If an equilibrium constant is very small,the forward reaction is favored
(iii)If an equilibrium constant is neither large nor small,appreciable quantities of all species are present at equilibrium

A)iii only
B)i and ii
C)ii and iii
D)All statements are incorrect
E)All statements are correct

Question 27

If one is trying to change the amount of reactants and products in a gaseous equilibrium system,which of the following will probably not have the desired effect?

A)addition of a catalyst
B)addition of a reactant
C)removal of a product
D)altering the temperature
E)changing the volume of the container

Question 28

In writing the expression for the equilibrium constant for a reaction,which of the following should not be done?

A)The concentration of products is placed in the numerator.
B)The concentration of reactants is placed in the demoninator.
C)There are terms for liquids,gases and solutions are included but not solids.
D)The coefficients from the chemical reaction are the exponents for the concentration term.
E)All of these are correct and should be observed.

Question 29

Choose the correct equilibrium constant expression for the equilibrium H₂(g)+ I₂(g) 2 HI(g)

A)K =
B)K =
C)K =
D)K =
E)K =

Question 30

Choose the correct equilibrium constant expression for the equilibrium CO(g)+ Cl₂(g) COCl₂(g).

A)K =
B)K =
C)K =
D)K =
E)K =

Question 31

Calculate the molar solubility of aluminum phosphate in water given that K_sp = 1.3 *10^-20.

A)1.1 * 10^-10 M
B)1.5 *10^-7 M
C)1.7 *10^-40 M
D)5.9 * 10³⁹ M
E)7.7 * 10¹⁹ M

Question 32

If an aluminum nitrate solution is added to a sodium fluoride solution the following equilibrium will be reached: Al³⁺(aq)+ 6 F^-(aq) AlF₆^3-(aq).For this equilibrium,K = 5.0 *10²³.Choose the correct equilibrium constant and the correct direction favored at equilibrium.

A)K = reverse
B)K = forward
C)K = reverse
D)K = forward
E)K = forward

Question 33

Choose the correct equilibrium constant expression for the hypothetical equilibrium 2 A(g)+ 3 B(g) 4 C(g)+ 5 D(g).

A)K =
B)K =
C)K =
D)K =
E)K =

Question 34

If the position of equilibrium shifts to the left,what will happen?

A)The concentration of products will increase
B)The concentration of reactants will increase
C)The temperature will rise
D)The temperature will decrease
E)The concentrations of both products and reactants will increase

Question 35

Calculate the molar solubility of magnesium fluoride (K_sp = 6.9 *10^-9)in a solution that also 0.010 M NaF.

A)6.9 * 10^-5 M
B)6.9 *10^-7 M
C)6.9 * 10^-11 M
D)1.7 *10^-5 M
E)3.5 * 10^-7 M

Question 36

Consider the hypothetical reaction A₂ + B₂ 2 AB When will the forward reaction rate be at a maximum,and when will the reverse reaction rate be at a maximum?

A)The forward reaction rate will be at a maximum when equilibrium is established,and the reverse reaction rate will be at a maximum when equilibrium is established
B)The forward reaction rate will be at a maximum when equilibrium is established,and the reverse reaction rate will be at a maximum at time zero
C)The forward reaction rate will be at a maximum at time zero,and the reverse reaction rate will be at a maximum when equilibrium is established
D)The forward reaction rate will be at a maximum between time zero and when equilibrium is established,and the reverse reaction rate will be at a maximum when equilibrium is established
E)The forward reaction rate will be at a maximum when equilibrium is established,and the reverse reaction rate will be at a maximum between time zero and when equilibrium is established

Question 37

Choose the correct equilibrium constant expression for the equilibrium 2 H₂(g)+ O₂(g) 2 H₂O( ).

A)K =
B)K =
C)K =
D)K =
E)K =

Question 38

Predict what will happen if the partial pressure of nitrogen is increased after the reaction N₂(g)+ 3 H₂(g) 2 NH₃(g)has reached equilibrium.

A)The position of equilibrium will shift to the left
B)The molar concentration of H₂ will increase
C)The partial pressure of H₂ will increase
D)The concentration of NH₃ will decrease
E)More ammonia will form

Question 39

What will happen to the position of equilibrium if the volume of the system is decreased in the reaction shown? N₂(g)+ 3 H₂ 2 NH₃(g)

A)It will shift to the left
B)There will be no shift in the position of equilibrium
C)The position will shift left and then return to its original place
D)It will shift to the right
E)It will shift so that the system volume is increased again

Question 40

Choose the correct equilibrium constant expression for the equilibrium 4 NO(g)+ 6 H₂O(g) 4 NH₃(g)+ 5 O₂(g)

A)K =
B)K =
C)K =
D)K =
E)K =

Question 41

Find the pH of a 0.10 M solution of benzoic acid,C₆H₅COOH,if the solution is also 0.15 M in C₆H₅COO^-.K_a = 6.3 *10^-5.

A)9.62
B)5.20
C)4.02
D)4.20
E)4.38

Question 42

What is the pH of a 0.20 M solution of nitrous acid? K_a = 4.5 *10^-4

A)9.02
B)4.66
C)4.05
D)2.02
E)0.70

Question 43

K_a = 1.8 *10^-5 for the ionization of HC₂H₃O₂(aq).Determine the [HC₂H₃O₂]/[C₂H₃O₂^-] ratio that will produce a buffer at pH = 5.00.

A)3.6 * 10^-6
B)9.0 *10^-5
C)0.18
D)0.56
E)1.8

Question 44

Which of the following correctly expresses K_a for the weak acid HF(aq)?

A)K_a = [HF]
B)K_a =
C)K_a =
D)K_a = [H⁺][F^-]
E)K_a =