Deck 7: Chemical Reactions: Energy, rates, and Equilibrium

Question 1

Based on the reaction shown,which statement is true?
S + O₂ → SO₂ + 70.8 kcal

A)70.8 kcal are produced when 1 g of sulfur reacts.
B)70.8 kcal are consumed when 1 g of sulfur reacts.
C)70.8 kcal are produced when 32.1 g of sulfur reacts.
D)70.8 kcal are consumed when 32.1 g of sulfur reacts.
E)70.8 kcal are produced when 1 g of sulfur dioxide is produced.

Answer 1

70.8 kcal are produced when 32.1 g of sulfur reacts.

Question 2

To simplify comparisons,the energy value of fuels is expressed in units of

A)kcal.
B)kcal/mol.
C)kcal/g.
D)kcal/L.
E)some other unit.

Answer 2

kcal/g.

Question 3

A reaction is said to be ________ if the bonds formed during the reaction are stronger than the bonds broken.

A)exothermic
B)endothermic
C)exergonic
D)endergonic
E)spontaneous

Answer 3

exothermic

Question 4

Based on the reaction shown,which statement is true?
P₄(s)+ 10 Cl₂(g)→ 4 PCl₅(s)ΔH = -435.2 kcal

A)When 1 mol P₄(s)reacts,435.2 kcal are released.
B)When 1 mol PCl_5(s) is produced,435.2 kcal are released.
C)When 30.97 g P₄(s)react,435.2 kcal are released.
D)When 123.88 g P₄(s)react,435.2 kcal are consumed.
E)When 208.22 g PCl_5(s) are produced,435.2 kcal are consumed.

Question 5

Consider the reaction shown:
N₂ + O₂ → 2 NO ΔH = 43.2 kcal
When 50.0 g of N₂ react,________ kcal will be ________.

A)43.2;produced
B)77.1;consumed
C)77.1;produced
D)2160;consumed
E)2160;produced

Question 6

The scientific principle which explains the observation that the amount of heat transfer accompanying a change in one direction is numerically equal but opposite in sign to the amount of heat transfer in the opposite direction is

A)the Law of Conservation of Energy.
B)the Law of Conservation of Mass.
C)the Law of Conservation of Mass and Energy.
D)the Law of Definite Proportions.
E)Avogadro's Law.

Question 7

All of the statements regarding the symbol "ΔH" are correct except it

A)represents the difference between the energy used in breaking bonds and the energy released in forming bonds in a chemical reaction.
B)can be called heat of reaction.
C)can be called enthalpy change.
D)can be called entropy change.
E)has a negative value for an exothermic reaction.

Question 8

Consider the reaction shown:
P₄(s)+ 10 Cl₂(g)→ 4 PCl₅(s)+ 452 kcal
When 50.00 g of P₄ react,________ kcal will be ________.

A)182.4;consumed
B)452.0;produced
C)729.7;produced
D)182.4;produced
E)452.0;consumed

Question 9

If heat is consumed during a reaction,the reaction is said to be

A)endothermic.
B)exothermic.
C)endergonic.
D)energetic.
E)can't tell.

Question 10

Consider the reaction shown:
452 kcal + 4 PCl₅(s)→ P₄(s)+ 10 Cl₂(g)
This reaction is ________ because the sign of ΔH is ________.

A)endothermic;positive
B)exothermic;positive
C)endothermic;negative
D)exothermic;negative
E)exothermic;neither positive nor negative

Question 11

A process or reaction which releases heat to the surroundings is said to be

A)conservative.
B)endothermic.
C)exothermic.
D)isothermal.
E)exergonic.

Question 12

Which of the following contains kinetic energy?

A)bicylce at the top of a hill
B)ball laying on the ground
C)a moving car
D)a battery
E)a piece of chocolate

Question 13

Consider the reaction shown:
2 CO(g)+ O₂(g)→ CO₂(g)+ 135.2 kcal
This reaction is ________ because the sign of ΔH is ________.

A)endothermic;positive
B)exothermic;positive
C)endothermic;negative
D)exothermic;negative
E)exothermic;neither positive nor negative

Question 14

Which of the following contains potential energy?

A)person riding a bicycle
B)a book on a table
C)a bouncing ball
D)a kid jumping rope
E)dancing

Question 15

A process or reaction which takes in heat from the surroundings is said to be

A)conservative.
B)endothermic.
C)exothermic.
D)isothermal.
E)endergonic.

Question 16

Based on the reaction shown,which statement is true?
N₂ + O₂ → 2 NO ΔH = 43.2 kcal

A)43.2 kcal are consumed when 1.00 g of N₂ reacts.
B)43.2 kcal are consumed when 1.00 g of O₂ reacts.
C)43.2 kcal are consumed when 1.00 mole of O₂ reacts.
D)43.2 kcal are produced when 1.00 mole of NO is produced.
E)43.2 kcal are consumed when 1.00 g of NO is produced.

Question 17

Consider the reaction shown:
304.0 kcal + 4 PCl₃(l)→ P₄(s)+ 6 Cl₂(g)
When 50.00 g of PCl₃ react,________ kcal will be ________.

A)304.0;produced
B)27.67;produced
C)304.0;consumed
D)110.7;consumed
E)27.67;consumed

Question 18

Based on the bond energies given for each of the following which is the most stable?

A)O=O 498 kJ/mol
B)C=O 745 kJ/mol
C)C=C 614 kJ/mol
D)C≡C 839 kJ/mol
E)N≡N 946 kJ/mol

Question 19

Consider the reaction shown:
C₃H₈ + 5 O₂ → 3 CO₂ + 4 H₂O + 488 kcal
We can say that this reaction is ________ and that the sign of ΔH is ________.

A)endothermic;positive
B)exothermic;positive
C)endothermic;negative
D)exothermic;negative
E)exothermic;neither positive nor negative

Question 20

Based on the reaction shown,which statement is true?
4 PCl₃(l)→ P₄(s)+ 6 Cl₂(g)ΔH = 304.0 kcal

A)When 1 mol PCl₃(l)reacts,304.0 kcal are released.
B)When 1 mol P₄(s)is produced,304.0 kcal are consumed.
C)When 548.56 g PCl₃(l)react,304.0 kcal are released.
D)When 137.14 g PCl₃(l)react,304.0 kcal are consumed.
E)When 123.88 g P₄(s)are produced,304.0 kcal are released.

Question 21

A reaction which is unfavorable with respect to entropy,but favorable with respect to enthalpy could

A)occur at any temperature.
B)not occur regardless of temperature.
C)occur at low temperatures but not at higher temperatures.
D)occur at high temperatures but not at lower temperatures.
E)none of the above

Question 22

Consider the endothermic reaction:
N₂(g)+ 2 H₂(g)→ N₂H₄(l)
The entropy change of this reaction is ________ and the enthalpy change is ________,so at a very high temperature,this reaction is probably ________.

A)favorable;unfavorable;nonspontaneous
B)favorable;unfavorable;spontaneous
C)unfavorable;unfavorable;spontaneous
D)unfavorable;unfavorable;nonspontaneous
E)unfavorable;favorable;spontaneous

Question 23

How much heat is released during the combustion of methane using the given bond dissociation energies:
CH₄ + 2 O₂ → CO₂ + 2H₂O
Number and types of bonds in each molecule:
CH₄ (4 C-H bonds);O₂ (1 O=O); (2 C=O bonds); (2 O-H bonds).
Bond dissociation energies:
C-C (347 kJ/mol);C-H (413 kJ/mol);O=O (498 kJ/mol;C=O (799 kJ/mol);O-H (467 kJ/mol)

A)-382 kJ
B)-8181 kJ
C)282 kJ
D)818 kJ
E)696 kJ

Question 24

In the process of dissolving sugar in water,the entropy increases.This means that the sign of ΔS is ________,and that the randomness of the system ________.

A)undetermined;increases
B)positive;decreases
C)positive;increases
D)negative;decreases
E)negative;increases

Question 25

A process which is unfavorable with respect to enthalpy,but favorable with respect to entropy could

A)occur at low temperatures,but not at higher temperatures.
B)occur at high temperatures,but not at lower temperatures.
C)not occur regardless of temperature.
D)occur at any temperature.
E)none of the above

Question 26

Entropy is used to

A)explain how energy is stored.
B)explain how an exothermic reaction can become endothermic.
C)indicate the disorder of a system.
D)explain why most chemical reactions are exothermic.
E)none of the above

Question 27

The label on a package of cookies states that there are 100 calories per serving.Explain the different meanings of this statement to a chemist and to a nutritionist.Be sure your answer explains the difference between kilocalories and Calorie.

Question 28

Which of the following processes involve an increase in entropy of the system?
I.Mothballs vaporize in a closet.
II.Blocks are assembled into a house.
III.Crystals grow from a sugar solution.
IV.Recyclable plastics are sorted.
V.Cake mix is manufactured from five basic ingredients.

A)II,IV
B)I,II,III
C)II,III,IV
D)I,V
E)I,III,V

Question 29

A reaction that is spontaneous can be described as

A)proceeding in both the forward and reverse directions.
B)having the same rate in both the forward and reverse directions.
C)releasing heat to the surroundings.
D)proceeding without external influence once it has begun.
E)increasing in disorder.

Question 30

Which of the following states of matter should have the lowest entropy value?

A)a crystalline solid
B)a liquid
C)a gas
D)Two of these have virtually the same entropy.
E)all of the above

Question 31

All of the statements regarding the symbol ΔG are true except it

A)refers to the free energy of the reaction.
B)allows us to predict the spontaneity of a reaction.
C)allows us to identify an exothermic reaction.
D)allows us to identify an endergonic reaction.
E)describes the effect of both enthalpy and entropy on a reaction.

Question 32

Entropy can be defined as the

A)amount of energy required to rearrange chemical bonds.
B)amount of energy required to initiate a reaction.
C)number of chemical bonds which are changed during a reaction.
D)state of equilibrium in a system.
E)amount of disorder in a system.

Question 33

Calculate the enthalpy for the combustion of propane shown using the given bond dissociation energies:
C₃H₈ + 5 O₂ → 3 CO₂ + 4H₂O
Number and types of bonds in each molecule:
C₃H₈ (2 C-C,8 C-H bonds);O₂ (1 O=O); (2 C=O bonds); (2 O-H bonds).
Bond dissociation energies:
C-C (347 kJ/mol);C-H (413 kJ/mol);O=O (498 kJ/mol;C=O (799 kJ/mol);O-H (467 kJ/mol)

A)-1962 kJ
B)1962 kJ
C)-2042 kJ
D)-50 kJ
E)-1242 kJ

Question 34

A solid sample at room temperature spontaneously sublimes forming a gas.This change in state is accompanied by which of the changes in the sample?

A)Entropy and energy decrease.
B)Entropy and energy increase.
C)Entropy decreases and energy increases.
D)Entropy increases and energy decreases.

Question 35

2 Al₂O₃(s)→ 4 Al(s)+ 3 O₂(g)ΔG = +138 kcal
Consider the contribution of entropy to the spontaneity of this reaction.As written,the reaction is ________,and the entropy of the system ________.

A)spontaneous;increases
B)spontaneous;decreases
C)non-spontaneous;increases
D)non-spontaneous;decreases
E)non-spontaneous;does not change

Question 36

For the reaction given below,what quantity of heat will be produced if 90.0 g of C₃H₈ are consumed in the reaction?
C₃H₈ + 5 O₂ → 3 CO₂ + 4 H₂O + 488 kcal

A)996 kcal
B)488 kcal
C)332 kcal
D)239 kcal
E)976 kcal

Question 37

Calculate the enthalpy for the following reaction: N₂ + O₂ → 2 NO given the following bond dissociation energies:
N₂ = 226 kcal/mol O₂ = 119 kcal/mol NO = 145 kcal/mol.

A)55 kcal/mol
B)-55 kcal/mol
C)235 kcal/mol
D)-235 kcal/mol

Question 38

All of the statements are true for spontaneous reactions except

A)the value of ΔG is less than zero.
B)the value of ΔG is unaffected by a catalyst.
C)they are said to be exergonic.
D)if the enthalpy change is unfavorable,they occur at a high temperature.
E)the reaction rate is determined by the value of ΔG.

Question 39

All of the statements concerning free energy and spontaneity are true except

A)if the value of ΔG for a reaction is 55.2 kcal,the value of ΔG for the reverse reaction will be -55.2 kcal.
B)if the value of ΔG for a reaction is negative,the reaction is said to be spontaneous.
C)a reaction which is nonspontaneous at low temperature cannot be spontaneous at higher temperatures.
D)enthalpy and entropy are of equal importance in determining the spontaneity of a reaction.
E)the speed of a reaction is not influenced by its spontaneity.

Question 40

The concept of free energy allows prediction of spontaneity of a process by considering the changes in ________ and ________ during the process.

A)enthalpy;entropy
B)enthalpy;mass
C)entropy;mass
D)enthalpy;temperature
E)entropy;temperature

Question 41

Which statement best describes the way a catalyst works?

A)It decreases the value of ΔH.
B)It increases the value of ΔH.
C)It decreases the value of E_act.
D)It increases the value of E_act.
E)It increases the value of ΔG.

Question 42

Which of the following statements can be assumed to be true about how reactions occur?

A)Catalysts must be present in the reaction.
B)Energy must be absorbed as the reaction proceeds.
C)Reactant particles must collide with each other.
D)More than one statement can be true.

Question 43

Activation energy can best be described as the

A)energy level of the products.
B)maximum energy level of the reaction.
C)energy level of the reactants.
D)difference in energy between reactants and products.
E)difference in energy between reactants and the maximum energy.

Question 44

Select the correct figure to match the description.
A slow reaction with a negative free energy change

A)
B)
C)
D)
E)

Question 45

For a chemical reaction to occur,all of the following must happen except

A)chemical bonds in the reactants must break.
B)reactant particles must collide with enough energy for change to occur.
C)reactant particles must collide with the correct orientation.
D)a large enough number of collisions must occur.
E)chemical bonds in the products must form.

Question 46

Which factors would increase the rate of a chemical reaction?
I.Increasing the temperature
II.Removing products as they are formed
III.Adding a catalyst

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

Question 47

In the reaction energy diagrams shown,reaction A is ________,and it occurs ________ reaction B.

A)endergonic;faster than
B)exergonic;faster than
C)endergonic;slower than
D)exergonic;slower than
E)exergonic;at the same rate as

Question 48

Which of the following can affect the activation energy of a reaction?

A)increase in concentration of products
B)increase in concentration of reactants
C)surface area of reactants
D)use of a catalyst
E)temperature of the reaction

Question 49

Sketch a diagram to illustrate the role of orientation in determining whether a collision between molecules of two different diatomic elements will lead to formation of a compound.How could you illustrate the influence of energy considerations on this reaction?

Question 50

Select the correct figure to match the description.
A fast reaction with a small positive free energy change

A)
B)
C)
D)
E)

Question 51

The function of a catalyst in a reaction system is to

A)increase the yield of product.
B)decrease the amount of heat produced.
C)decrease the amount of energy consumed in the reaction.
D)increase the rate of the reaction.
E)decrease the amount of reactants consumed.

Question 52

In the reaction A + B → AB,which of the following will not increase the rate?

A)adding A
B)adding B
C)increasing the temperature
D)decreasing the temperature
E)adding a catalyst

Question 53

In the reaction energy diagrams shown,reaction B is ________,and it occurs ________ reaction B.

A)endergonic;faster than
B)exergonic;faster than
C)endergonic;slower than
D)exergonic;slower than
E)exergonic;at the same rate as

Question 54

Select the correct figure to match the description.
A slow reaction with a large negative free energy change

A)
B)
C)
D)
E)

Question 55

Which of the following will affect all reaction rates?

A)the temperature of the reactants
B)the concentrations of the reactants
C)the presence of a catalyst
D)All are correct.

Question 56

Select the correct figure to match the description.
A slow reaction with a large positive free energy change

A)
B)
C)
D)
E)

Question 57

A rapid reaction is distinguished by

A)being unaffected by catalysts.
B)having a large heat of reaction.
C)having a small heat of reaction.
D)having a large value of activation energy.
E)having a small value of activation energy.

Question 58

Reaction rates are determined by all of the following factors except the

A)number of collisions between molecules.
B)force of collisions between molecules.
C)orientation of collisions between molecules.
D)spontaneity of the reaction.
E)activation energy of the reaction.

Question 59

Select the correct figure to match the description.
A fast reaction with a large negative free energy change

A)
B)
C)
D)
E)

Question 60

Which factors would decrease the rate of a reaction?
I.Lowering the temperature
II.Increasing the concentration of reactants
III.Adding a catalyst

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

Question 61

In order to determine if a reaction is at equilibrium which of the following must be true?

A)The concentrations of the reactants and products must be equal.
B)The concentration of the products must be greater than the reactants.
C)The forward and reverse reactions have stopped.
D)The rate at which the forward and reverse reactions are proceeding are equal.
E)All of the above are true.

Question 62

For the following reaction,increasing the pressure will cause the equilibrium to
2 SO₂(g)+ O₂(g) 2 SO₃(g)+ heat

A)shift to the right,towards products.
B)shift to the left,towards reactants.
C)remain unchanged,but the reaction mixture will get warmer.
D)remain unchanged,but the reaction mixture will get cooler.
E)Pressure has no effect on equilibrium.

Question 63

Calculate the equilibrium constant for the reaction below if a tank was found to contain 0.106 M O₂,0.00652 M SO_3, and 0.00129 M SO₂.
2 SO₃(g)2 SO₂(g)+ O₂(g)

A)6.78 × 10^-2
B)1.34 × 10^-2
C)4.15 × 10^-3
D)4.35 × 10^-2
E)9.66 × 10^-3

Question 64

Which process is not likely to be considered reversible?

A)a round trip to Las Vegas
B)melting wax to make candles
C)a reaction using the symbol "↔"
D)cutting down a tree
E)dissolving salt in water

Question 65

Match the following.
A process or reaction which releases heat

A)exothermic
B)activation energy
C)chemical equilibrium
D)endergonic
E)exergonic
F)endothermic

Question 66

Match the following.
A process or reaction that has a negative value of ΔG

A)exothermic
B)activation energy
C)chemical equilibrium
D)endergonic
E)exergonic
F)endothermic

Question 67

Consider the reaction:
A + 2 B 2 C + D
The equilibrium expression for this reaction is:

A)
B)
C)
D)
E)

Question 68

2 SO₂(g)+ O₂(g) 2 SO₃(g)+ heat K = 4.8 ×
Which statement about this system is not true?

A)At equilibrium
Is the predominant substance.
B)Heating the system will cause breakdown of
.
C)Adding
Will cause an increase in the amount of

.
D)Removing
Will cause an increase in the amount of

.
E)The large value of K means that the reaction essentially goes to completion.

Question 69

Write the equilibrium expression for the following reaction:
4 HNO₃(l)4 NO₂(g)+ 2 H₂O(g)+ O₂(g)

A)[NO₂]⁴ [H₂O]² [O₂]/[HNO₃]⁴
B)1/[NO₂]⁴ [H₂O]² [O₂]
C)[HNO₃]^4/[NO₂]⁴ [H₂O]² [O₂]
D)[NO₂]⁴ [H₂O]² [O₂]
E)[NO₂]⁴ + [H₂O]² + [O₂]

Question 70

Which change to this reaction system would cause the equilibrium to shift to the right?
N₂(g)+ 3 H₂(g) 2 NH₃(g)+ heat

A)addition of a catalyst
B)addition of NH₃(g)
C)removal of H₂(g)
D)heating the system
E)lowering the temperature

Question 71

The position of the equilibrium for a system where K = 4.6 × 10^-15 can be described as being favored to ________;the concentration of products is relatively ________.

A)the right;large
B)the right;small
C)the left;large
D)the left;small
E)neither direction;large

Question 72

Match the following.
A process or reaction which consumes heat

A)exothermic
B)activation energy
C)chemical equilibrium
D)endergonic
E)exergonic
F)endothermic

Question 73

Consider the reaction:
2 CO(g)+ O₂(g) 2 CO₂(g)
The equilibrium expression for this reaction is:

A)
B)
C)
D)
E)

Question 74

Match the following.
A process or reaction that has a positive value of ΔG

A)exothermic
B)activation energy
C)chemical equilibrium
D)endergonic
E)exergonic
F)endothermic

Question 75

Diatomic nitrogen is added to the equilibrium system:
N₂(g)+ H₂(g) 2 NH₃(g)+ heat
When a new equilibrium is established the concentration of H₂ will be ________ the amount at the original equilibrium,and the amount of NH₃ will be ________ the amount at the original equilibrium.

A)greater than;greater than
B)greater than;less than
C)less than;greater than
D)less than;less than
E)Both changes will be impossible to determine.

Question 76

Which of the following conditions characterizes a system in a state of chemical equilibrium?

A)Concentrations of reactants and products are equal.
B)Rate of forward reaction has dropped to zero.
C)Reactants are being consumed at the same rate they are being produced.
D)Reactant molecules no longer react with each other.
E)Product concentrations are greater than reactant concentrations.

Question 77

If we add a catalyst to the following equation,CO + H₂O + heat CO₂ + H₂,which way will the equilibrium shift?

A)to the left
B)no effect
C)to the right
D)not enough information

Question 78

Given the following reaction,the equilibrium expression will be:
C(s)+ 2 H₂(g) CH₄(g)

A) [CH₄]/[C] [H₂]²
B)k[C][H₂]
C)[CH₄]/[H₂]²
D)[H₂]²[C]/[CH₄]
E) [CH₄][C] [H₂]²

Question 79

Match the following.
A state in which the rate of the forward reaction is exactly equal to the rate of the reverse reaction

A)exothermic
B)activation energy
C)chemical equilibrium
D)endergonic
E)exergonic
F)endothermic

Question 80

When a reaction system is at equilibrium

A)there is no more chemistry happening.
B)the amounts of reactants and products are exactly equal.
C)the reaction rate in the forward direction is at a maximum.
D)the reaction rate in the reverse direction is at a minimum.
E)the rates of the reaction in the forward and reverse directions are exactly equal.