Deck 13: When Reactants Turn Into Products

Question 1

Which of the following is not true when the temperature of the reaction mixture is decreased?

A) The average kinetic energy of both the reactant and product molecules is decreased.
B) The rate of the reaction is decreased.
C) The fraction of reactant molecules that have a low kinetic energies is increased.
D) The activation energy of the reaction is increased.

Answer 1

The activation energy of the reaction is increased.

Question 2

Which statement is true about the reaction energy profile?

A) plots the relative energies of both the reactants and products
B) plots energy on the y-axis
C) traces the progress of the reaction on the x-axis
D) All of the above are true.

Answer 2

All of the above are true.

Question 3

Which of the following is true about enzymes?

A) They speed up reactions in a selective fashion.
B) They are very large proteins.
C) They contain specifically shaped pockets that fit only specific reactant molecules.
D) All of the above are true.

Answer 3

All of the above are true.

Question 4

Consider the reaction X → Y with the following data: Energy of reactants = 50 kJ/mole;
Energy of reaction = -30 kJ/mole;
Energy of transition state = 90 kJ/mole.
The energy of products for the reaction is ________ kJ/mole.

A) -30
B) 20
C) 30
D) 80

Question 5

Which of the following is not a substitution reaction?

A) NaOH + HCl→ NaCl + H₂O
B) AgNO₃ + NaCl → NaNO₃ + AgCl
C) 2Fe + O₂ → 2FeO
D) CH₃OH + HCl → CH₃Cl + H₂O

Question 6

In order for a chemical reaction to occur, ________.

A) the reactants must be in sufficient concentration
B) the products must be of lower energy than the reactants
C) the reactants must be of lower energy than the products
D) the reactants must possess sufficient energy to overcome the barrier of the activation energy

Question 7

Which of the following is an example of a substitution reaction?

A) OH + → Br +
B) - + + → + + O
C) 2Mg + → 2MgO
D) + → 2HI

Question 8

Which of the following does not influence the speed of a chemical reaction?

A) concentration of the reactants
B) molecular mass of the reactants
C) surface area of solid reactants
D) temperature

Question 9

Which of the following is endothermic?

A) melting ice
B) freezing water
C) dry ice formed from carbon dioxide
D) condensing water vapor

Question 10

If the products have a higher energy than the reactants ________.

A) the reaction is exothermic
B) the reaction is endothermic
C) the reactants have less energy than the products
D) both B and C

Question 11

Consider the reaction C → D with the following data: Energy of reactants = 30 kJ/mole;
Energy of products = 20 kJ/mole;
Energy of transition state = 60 kJ/mole.
The reaction is ________, has a heat of reaction of ________kJ/mole, and the energy of activation is ________ kJ/mole.

A) exothermic; -10; 30
B) endothermic; 10; 30
C) exothermic; 40; 30
D) endothermic; 40; 30

Question 12

Which of the following "adjustments" can be made to a chemical reaction system to increase the rate of reaction?

A) increase the reaction temperature
B) increase the concentrations of the reactants
C) add a catalyst
D) All of the above will increase the rate of reaction.
E) None of the above will increase the rate of reaction.

Question 13

Consider the reaction X → Y with the following data: Energy of reactants = 25 kJ/mole;
Energy of products = 75 kJ/mole;
Energy of transition state = 100 kJ/mole.
The energy of activation for the reverse reaction is ________ kJ/mole.

A) 25
B) 50.
C) 75
D) 100

Question 14

If the reaction has a negative overall energy change, then ________.

A) the reaction is exothermic
B) energy is absorbed by the reactants
C) the reaction is endothermic
D) the products are not stable

Question 15

Consider the reaction A → B with the following data: Energy of reactants = 50 kJ/mole;
Energy of products = 70 kJ/mole;
Energy of transition state = 80 kJ/mole.
The reaction is ________, has a heat of reaction of ________ kJ/mole, and the energy of activation is ________ kJ/mole.

A) exothermic; 20; 30
B) endothermic; 20; 30
C) exothermic; 30; 20
D) endothermic; 30; 20

Question 16

Which of the following represents a reaction coordinate diagram for a chemical reaction whose ΔErxn = 0?

A)
B)
C)
D)

Question 17

Which of the following reaction coordinate diagrams represents a chemical reaction that is exothermic?

A)
B)
C)
D)

Question 18

The difference in energy between the reactants and products in a chemical reaction is called ________.

A) the heat of reaction
B) the activation energy
C) the energy of products
D) either B or C

Question 19

Which of the following reaction coordinate diagrams represents a chemical reaction that is endothermic?

A)
B)
C)
D)

Question 20

Which of the following is an exothermic reaction?

A) burning propane gas in a barbecue
B) burning gasoline when driving a car
C) creating an explosion by detonating nitroglycerine
D) All of the above are exothermic reactions.

Question 21

Which of the following is true about the activation energy?

A) It may increase by decreasing the temperature.
B) It may decrease by decreasing the temperature.
C) It may increase by increasing the concentration of reactants.
D) It is practically independent of both temperature and concentration of reactants.

Question 22

Which of the following is true about a catalyst?

A) It increases the rate of a reaction.
B) It can be used in trace amounts.
C) It is not used up in the process.
D) All of the above are true.

Question 23

Which of the following may be considered as biochemical catalysts?

A) carbohydrates
B) DNA
C) enzymes
D) lipids

Question 24

If the kinetic energy of the reactant molecules is not high enough to overcome the activation energy barrier, ________.

A) the reverse reaction will occur
B) no reaction takes place
C) the reaction will occur anyway
D) the products will form at a slower rate

Question 25

This factor depends on concentration and can be manipulated.

A) the total number of collisions that occur per unit time
B) the fraction of collisions with energy larger than the energy of activation
C) the fraction of collisions with the proper orientation
D) All of the above are correct.

Question 26

Which of the following does not affect the rate of a reaction?

A) the concentration of the reactants
B) the energy of activation
C) the temperature
D) the external pressure

Question 27

In each of the following diagrams, the x-axis is the reaction coordinate and the y-axis is the potential energy. Which diagram corresponds to a reaction that has an activation energy of 35 kJ and an overall reaction energy of -110 kJ?

A)
B)
C)
D)

Question 28

The energy of activation may be affected by ________.

A) increasing the concentration of the reactants
B) higher temperature
C) decreasing the concentration of the reactants
D) the presence of a catalyst

Question 29

In a catalyzed reaction the activation energy is ________ when compared to the uncatalyzed reaction.

A) identical
B) less
C) more
D) either less or more depending on the reaction

Question 30

The units for the rate of a reaction are ________.

A) concentration per unit of time
B) concentration multiplied by the unit of time
C) unit of time per unit of concentration
D) One cannot say with certainty since rate laws vary from reaction to reaction.

Question 31

In the diagram above, the containers shown (Box A and Box B) contain exactly the same number of the same reactant molecules and are at the same temperature. In which box will the rate of reaction be faster?

A) Box A
B) Box B
C) Rate is about the same in each box.
D) No way to tell which is faster from this picture.

Question 32

Generally in a biochemical reaction the first step involves ________.

A) the reaction of the enzyme with the active site of the substrate
B) the reaction of the substrate with the active site of the enzyme
C) the reaction of the substrate with the enzyme-substrate complex
D) the reaction of the enzyme with the enzyme-substrate complex

Question 33

In the diagram above, the two containers shown (Box A and Box B) have exactly the same size (volume), are held at the same temperature, and contain the same reactant molecules (dots). In which box will the rate of reaction be faster?

A) Box A
B) Box B
C) The rate will be about the same in each box.
D) There is no way to tell which will be faster from this diagram.

Question 34

Which of the following can be done to increase the likelihood that a chemical reaction will take place?

A) decrease the average speed of the reacting molecules
B) induce more collisions between reacting molecules
C) remove all the water from the reaction mixture
D) break the reaction up into a series of steps

Question 35

In each of the following diagrams, the x-axis is the reaction coordinate and the y-axis is the potential energy. Which diagram corresponds to a reaction that has an activation energy of 40 kJ and an overall reaction energy of -125 kJ?

A)
B)
C)
D)

Question 36

The fraction of collisions with the proper orientation depends on ________.

A) the strength of the bonds that are to be broken
B) the molecular shape of the molecule
C) the concentration
D) both A and B

Question 37

The rate of a reaction may be increased by ________.

A) increasing the concentration of reactants
B) increasing the temperature
C) adding a catalyst
D) all of the above

Question 38

Which of the following factors could increase the reaction rate? 2A + B2 → 2AB
(I) decreasing the temperature
(II) adding a catalyst
(III) increasing the surface area of solid reactants

A) I and II
B) I, II, and III
C) I and III
D) II and III
E) III only

Question 39

Which of the following is not a term involved in determining the overall rate of a chemical reaction?

A) the total number of collisions per unit time
B) the total number of collisions in the gas phase
C) the fraction of collisions with energy greater than the activation energy
D) the fraction of collisions which occur with a favorable orientation

Question 40

Which of the following statements is true?

A) Lowering the concentration of the reactants increases the number of collisions.
B) Increasing the concentration of the reactants decreases the rate of reaction.
C) Increasing the collision rate increases the rate of the reaction.
D) Decreasing the collision rate occurs at higher temperatures.

Question 41

If the concentration of A is doubled while the concentration of B is unchanged, the rate will ________. A (g) + 3 B (g) → C (g) + 2 D (g)
Rate = k[A][B]3

A) stay the same
B) be reduced by a factor of 8
C) double
D) be increased by a factor of 8

Question 42

The slow step in the multistep mechanism of a reaction ________.

A) controls the rate at which the products are formed
B) is the only step that involves the breaking of bonds
C) is equally significant in measuring the rate
D) is insignificant in the formation of products

Question 43

An endothermic reaction usually leads to cooling.

Question 44

Which of the following statements regarding reaction mechanisms is true?

A) A mechanism is a series of steps whereby reactants are converted to products.
B) Reaction mechanisms must be determined experimentally.
C) Neither A nor B is true.
D) Both A and B are true.

Question 45

The following data was obtained at 100 °C. 2 Y (g) + X (g) → Z (g) The rate law for this reaction is ________..

A) Rate = k[Y]2[X]
B) Rate = k[Y][X]2
C) Rate = k[Y][X]
D) Rate = k[Y]2[X]2

Question 46

The order of the reaction with respect to A, B, and the total order respectively is ________. A + B → Products
Rate = k[A]3[B]0

A) 3, 1, 1
B) 3, 0, 2
C) 3, 0, 3
D) 3, 1, 4

Question 47

If the concentration of B is doubled while the concentration of A is unchanged, the rate will ________. A (g) + 3B (g) → C (g) + 2D (g)
Rate = k[A][B]3

A) stay the same
B) be increased by a factor of 6
C) double
D) be increased by a factor of 8

Question 48

Doubling the concentration of A leads to doubling the rate, while doubling the concentration of B has no effect on the rate. The rate equation is, therefore, ________. A + B → C

A) Rate = k[A][B]
B) Rate = k[A]
C) Rate = k[A]2
D) Rate = k[A]2[B]

Question 49

Doubling the concentration of A leads to doubling the rate, while doubling the concentration of B quadruples the rate. The rate equation is, therefore, ________. A + B → C

A) Rate = k[A][B]2
B) Rate = k[A]
C) Rate = k[A]2
D) Rate = k[A]2[B]

Question 50

The overall order is ________. Rate = k[A]2[B]1

A) -1
B) 0
C) 2
D) 3

Question 51

The overall order is ________. Rate = k[A]3[B]-1

A) -1
B) 0
C) 2
D) 3

Question 52

The following data was obtained at 20 °C. 2Y (g) → Z (g) The rate law for this reaction is ________.

A) Rate = k[Y]2
B) Rate = k[Y]
C) Rate = k[Y]0
D) Rate = k[Y]-1

Question 53

The overall order of this reaction is ________. A + B + C → Products
Rate = k[A]1[B]-1[C]2

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

Question 54

The order of the reaction with respect to A, B, and the total order respectively is ________. A + B → Products
Rate = k[A][B]

A) 1, 1, 1
B) 1, 1, 2
C) 1, 2, 2
D) 1, 2, 3

Question 55

The following data was obtained at 20 °C. X (g) → Y (g) The rate law for this reaction is ________.

A) Rate = k[X]2
B) Rate = k[X]
C) Rate = k[X]0
D) Rate = k[X]-1

Question 56

Which of the following statements is false?

A) The rate determining step is always the slowest step in a multistep mechanism.
B) The rate constant always changes with a variation in temperature.
C) The energy of activation affects the speed of reaction.
D) The rate of a reaction is independent of the concentration of reactants.

Question 57

Knowing the mechanism of a reaction is advantageous because one may influence its rate to make the reaction useful.

Question 58

The following data was obtained at 20 °C. 2W (g) → V (g) The rate law for this reaction is ________.

A) Rate = k[W]2
B) Rate = k[W]
C) Rate = k[W]0
D) Rate = k[W]-1

Question 59

The following data was obtained at 100 °C. 2Y (g) + X (g) → Z (g) The rate law for this reaction is ________.

A) Rate = k[Y]2[X]
B) Rate = k[Y][X]2
C) Rate = k[Y]3[X]
D) Rate = k[Y]3[X]0

Question 60

Which of the following responses contains the two rate factors that comprise the rate constant (k) for a given chemical reaction?

A) the temperature and the number of collisions per unit volume
B) the number of collisions per unit volume and the fraction of collisions with a favorable orientation
C) the number of collisions with energy greater than the activation energy and the fraction of collisions with a favorable orientation
D) the number of collisions with energy greater than the activation energy and the temperature

Question 61

Enzymes serve as catalysts in biochemical reaction systems.

Question 62

In an endothermic reaction, the top of the energy barrier to the products is a higher value than the top of the energy barrier to the reactants.

Question 63

A catalyst works by providing a new mechanism, higher in energy that the original reaction.

Question 64

The reaction energy profile can tell if a reaction is exothermic or endothermic.

Question 65

For chemical reactions to occur at all, "old" bonds must be broken and "new" bonds must form.

Question 66

The transition state for a reaction occurs at the bottom of the energy barrier.

Question 67

For an endothermic reaction, the value for ΔErxn is a negative number.

Question 68

The reaction: HCl + NaOH → H₂O + NaCl is a substitution reaction.

Question 69

A catalyst need not be present in large quantities.

Question 70

The value of Ea(reaction) is equal to the difference Ea(reactants) - Ea(products).

Question 71

A catalyst can be recovered at the end of the reaction.

Question 72

Adding a catalyst increases the rate of reaction by providing the additional energy needed to overcome a large energy of activation.

Question 73

For an exothermic reaction, the energy level of the products is lower than the energy level of the reactants..

Question 74

In an exothermic reaction, more energy is absorbed on the reactant bonds breaking than is released as the product bonds form.

Question 75

When the products are higher in energy than the reactants, the reaction is endothermic.

Question 76

A catalyst lowers the activation energy for a chemical reaction.

Question 77

If the forward reaction is exothermic, the reverse is endothermic.

Question 78

The magnitude (size) of the energy of activation for the reverse reaction is exactly identical as it is for the forward reaction in an exothermic (or endothermic) process.

Question 79

An exothermic reaction always leads to a release in energy.

Question 80

A lower energy of activation leads to more products favored in the reaction.