Ch6 Energy Changes, Reaction Rates, and Complete Test Bank

General, Organic and Biological Chemistry, 4e (Smith)

Chapter 6 Energy Changes, Reaction Rates, and Equilibrium

1) The law of conservation of energy states that ________.

A) the energy of the reactants and products in a chemical reaction are always equal

B) all chemical reactions are reversible

C) energy can be created, but not destroyed

D) energy cannot be created or destroyed

2) A chemical reaction requires 31.39 kJ. How many kilocalories does this correspond to?

A) 7,502 kcal

B) 7.502 kcal

C) 131.3 kcal

D) 0.1313 kcal

E) 31.39 kcal

3) A chemical reaction releases 55.2 kcal. How many kilojoules does this correspond to?

A) 231 kJ

B) 0.231 kJ

C) 13.2 kJ

D) 1,320 kJ

4) Which of the following energy quantities is equivalent to 578 J?

A) 5.78 × 105 kJ

B) 138 kcal

C) 0.138 kcal

D) 1.38 × 105 kcal

5) Which of the following energy quantities is equivalent to 11.9 kcal?

A) 1.19 × 105 cal

B) 49.8 J

C) 49.8 kJ

D) 2.84 × 103 kJ

6) Which of the following energy quantities is equivalent to 258 Cal?

A) 258 cal

B) 1080 J

C) 1080 kJ

D) 6.17 × 104 kJ

7) Which quantity represents the largest amount of stored energy?

A) 10 grams of fat

B) 10 grams of carbohydrate

C) 10 grams of protein

D) 5 grams of carbohydrate plus 5 grams of protein

E) 5 grams of protein plus 5 grams of fat

8) A peanut butter and jelly sandwich contains 9.00 g of fat, 6.00 g of protein, and 25.0 g of carbohydrate. How many Calories does this sandwich provide?

A) 205 Cal

B) 360 Cal

C) 160 Cal

D) 260 Cal

E) 190 Cal

9) Which bond is the strongest?

A) H–Br

B) H–Cl

C) H–F

D) H–I

10) Which bond is the weakest?

A) H–Br

B) H–Cl

C) H–F

D) H–I

11) Which term correctly describes a reaction in which the energy of the products is higher than the energy of the reactants?

A) Oxidation-reduction

B) Endothermic

C) Exothermic

D) Combustion

12) Consider the reaction: C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g), where ΔH = –531 kcal. Which statement concerning this reaction is true?

A) Heat is absorbed.

B) The bonds formed in the products are stronger than the bonds broken in the reactants.

C) The products are higher in energy than the reactants.

D) The reaction is endothermic.

13) Consider the reaction, C2H4(g) + H2(g) → C2H6(g), where ΔH = –137 kJ. How many kilojoules are released when 3.5 mol of C2H4 reacts?

A) 137 kJ are released

B) 570 kJ are released

C) 480 kJ are released

D) 2.0 × 103 kJ are released

14) Consider the reaction, C2H4(g) + H2(g) → C2H6(g), where ΔH = –137 kJ. How many kilojoules are released when 55.3 g of C2H4 reacts?

A) 137 kJ are released

B) 270. kJ are released

C) 1.13 × 103 kJ are released

D) 7.58 × 103 kJ are released

15) Consider the reaction, 3 NO2(g) + H2O(l) → 2 HNO3(aq) + NO(g), where ΔH = –137 kJ. How many kilojoules are released when 92.3 g of NO2 reacts?

A) 2.01 kJ are released

B) 2.75 × 102 kJ are released

C) 91.6 kJ are released

D) 1.26 × 104 kJ are released

16) Which of the following is a true statement about the energy diagram shown below?

A) A labels the Ea of the reaction and B labels ΔH of the reaction.

B) A labels the ΔH of the reaction and B labels Ea of the reaction.

C) C labels the activation energy.

D) D labels the reactants and E labels the products.

17) In the reaction: 2 C2H6(g) + 7 O2(g) → 4 CO2(g) + 6 H2O(g), increasing the concentration of C2H6(g) will ________.

A) increase the activation energy of the reaction

B) decrease the activation energy of the reaction

C) decrease the ΔH of the reaction

D) increase the reaction rate

E) decrease the reaction rate

18) Catalysts accelerate a reaction by ________.

A) lowering the enthalpy of the reaction

B) lowering the energy of activation

C) raising the enthalpy of the reaction

D) raising the energy of activation

19) Which value (if any) in each pair corresponds to a faster reaction?

A) Ea = 1 kcal

B) Ea = 10 kcal

C) Ea = 100 kcal

D) Reaction rate is independent of Ea value.

20) Which value (if any) in each pair corresponds to a slower reaction?

A) Ea = 1 kcal

B) Ea = 10 kcal

C) Ea = 100 kcal

D) Reaction rate is independent of Ea value.

21) What is the expression for the equilibrium constant for the reaction: 2 C2H6(g) + 7 O2(g)  4 CO2(g) + 6 H2O(g)?

A)

B)

C)

D)

22) An equilibrium constant with a value of 8.0 × 106 indicates that at equilibrium ________.

A) the reactants are favored

B) the products are favored

C) approximately equal concentrations of reactants and products are present

D) there are more reactants present than products

23) An equilibrium constant with a value of 1.5 × 10–9 indicates that at equilibrium ________.

A) the reactants are favored

B) the products are favored

C) approximately equal concentrations of reactants and products are present

D) there are more products present than reactants

24) Which K value below is consistent with an equilibrium system in which the products are favored?

A) K = 1

B) K = 5.2 x 104

C) K = 3.8 x 10–6

D) K = 0.100

25) Which K value below is consistent with an equilibrium system in which the reactants are favored?

A) K = 1

B) K = 1.8 x 103

C) K = 3.7 x 10–8

D) K = 500

26) When the pressure of a reaction at equilibrium decreases, in which direction does the equilibrium shift?

A) The equilibrium shifts in the direction that increases the number of moles of gas.

B) The equilibrium shifts in the direction that decreases the number of moles of gas.

C) The equilibrium does not shift.

D) The equilibrium shifts always shifts to the right.

E) The equilibrium shifts always shifts to the left.

27) For an endothermic reaction at equilibrium, increasing the temperature ________.

A) does not shift the equilibrium since K is a constant

B) increases the rate of the reverse reaction to form more reactants

C) increases the rate of the forward reaction to form more products

D) increases the rate of the reverse reaction to form more products

28) What is the gas phase chemical reaction that corresponds to the equilibrium constant expression shown below? 

A) 2 A + 4 B  2 C

B) A + B  C

C) 2 C 2 A + 4 B

D) 2 C  4 A + 2 B

E) 4 A + 2 B  2 C

29) The molecular art depicts the following reversible reaction at equilibrium: CO(g) + Cl2(g)   COCl2(g). What can be inferred about the equilibrium constant, K, for this reaction? 

A) K < 1

B) K ~ 1

C) K > 1

D) K = 0

30) The reversible reaction: PCl3(g) + Cl2(g)   PCl5(g), has K = 0.5. Based on the molecular art shown below, what can be inferred about the reaction conditions?  

A) The reaction has not yet reached equilibrium.

B) The reaction mixture is at equilibrium.

C) The reaction will shift to the left to reach equilibrium.

D) The forward reaction is favorable.

31) Consider the reaction: PCl3(g) + Cl2(g)  PCl5(g). If [PCl3] = 0.78 M, [Cl2] = 0.44 M, and [PCl5] = 0.88 at equilibrium, what is the value of K?

A) 0.39

B) 1.4

C) 2.6

D) 0.72

32) Consider the reaction: N2(g) + O2(g)   2 NO(g). If [N2] = 0.520 M, [O2] = 0.0662 M, and [NO] = 0.00956 at equilibrium, what is the value of K?

A) 3.60

B) 0.278

C) 377

D) 0.00265

33) A catalytic converter uses a catalyst to catalyze three reactions that clean up the exhaust from an auto engine. Which element is not used as a catalyst in catalytic converters?

A) Platinum

B) Rhodium

C) Sulfur

D) Palladium

34) Consider the combustion reaction of propane: C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g), where ΔH = –531 kcal. If 1.24 × 105 kcal of energy is released in the reaction, how many moles of propane were burned?

A) 234 mol of C3H8

B) 6.58 × 107 mol of C3H8

C) 0.00428 mol of C3H8

D) 0.0179 mol of C3H8

35) Consider the combustion reaction of propane: C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g), where ΔH = –531 kcal. If 6.70 × 104 kcal of energy is released in the reaction, how many grams of oxygen were consumed?

A) 63.1 g of O2

B) 2.02 × 104 g of O2

C) 12.6 g of O2

D) 404 g of O2

36) Which of the following will increase the rate of a reaction?

A) Increasing the temperature

B) Increasing the concentration of a reactant

C) Adding a catalyst

D) Ensuring that the reactants are properly aligned when they collide

E) All of these changes will increase the rate of a reaction.

37) Consider the reversible reaction at equilibrium: N2(g) + O2(g)   2 NO(g). What is the effect of removing some N2(g) from the equilibrium system?

A) The concentration of O2(g) increases

B) The concentration of O2(g) decreases

C) The concentration of NO(g) increases

D) The equilibrium system shifts to the right

38) Which statement about catalysts is NOT true?

A) A catalyst increases the rate of a chemical reaction.

B) A catalyst lowers the activation energy of a chemical reaction.

C) A catalyst lowers the ΔH of a chemical reaction.

D) A catalyst is recovered unchanged in the reaction it catalyzes.

39) Walking at a brisk pace burns off about 280 Cal/h. How long would you have to walk to burn off the Calories obtained from eating a candy bar that contained 3 g of protein, 12 g of fat, and 28 g of carbohydrates?

A) 55 minutes

B) 230 minutes

C) 50 minutes

D) 210 minutes

40) Consider the reaction: C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g), where ΔH = –531 kcal/mol. How much heat is released when 3.40 × 1020 molecules of C3H8(g) is burned?

A) 3.33 kcal

B) 0.300 kcal

C) 6.40 × 1017 kcal

D) 1.50 kcal

41) Which of the following is ALWAYS necessary for a chemical reaction to occur between two reactants, A and B?

A) Equal amounts of A and B must be present

B) A and B must be present in the same physical state

C) The reaction must be carried out at a temperature higher than room temperature

D) A and B must collide with the proper orientation and with a certain minimum amount of energy

42) Which of the following is NOT a reasonable assumption about the chemical reaction whose energy diagram is depicted below?

A) The activation energy for the reaction is 100kJ.

B) The reaction is exothermic.

C) ΔH= –25kJ

D) The reaction is favorable.

43) The rusting of iron is described by the reaction: 4 Fe(s) + 3 O2(g) → 2 Fe2O3(s). The formation of rust on an exposed piece of iron typically takes several months. Which of the following is NOT a reasonable assumption about this chemical reaction?

A) The formation of rust has a low reaction rate.

B) The formation of rust has a low activation energy.

C) The formation of rust would occur more slowly at higher altitudes where the concentration of oxygen is lower.

D) The formation of rust would occur faster in the warmer summer months than in the cooler winter months.

44) The rate of a chemical reaction increases with an increase in the concentration of one or more reactants. This is best explained by which statement?

A) The higher concentration of reactants increases the potential energy of the molecules.

B) The higher concentration of reactants increases the activation energy of the reaction.

C) The higher concentration of reactants increases the temperature of the molecules.

D) The higher concentration of reactants increases the frequency of collisions between molecules.

45) A reversible reaction has reached equilibrium when which condition is established?

A) the reverse reaction begins to occur

B) the concentrations of reactants and products become equal

C) all of the reactants have been converted into products

D) the forward and reverse reaction rates become equal

46) The hydrolysis of sucrose depicted below has K = 1.4 × 105. Which of the following is a reasonable assumption about this reaction once equilibrium is established?

sucrose + H2O   glucose + fructose

A) The equilibrium mixture contains equal amounts of sucrose, glucose, and fructose.

B) The equilibrium mixture contains mostly glucose and fructose.

C) The equilibrium mixture contains mostly sucrose.

D) The equilibrium shifts to the left due to the high value for K.

47) Which statement concerning the reversible reaction 2 NO2(g)  N2O4(g) is true?

A) NO2 is the product of the forward reaction.

B) The reverse reaction produces N2O4.

C) At the start of the reaction, the forward and reverse reaction rates are equal.

D) As the forward reaction progresses and more N2O4 is formed, the reverse reaction rate increases.

48) One step in the metabolism of glucose is depicted below. Which statement best describes how the equilibrium system would respond if the amount of dihydroxyacetone phosphate is decreased?

A) The system would shift to the left, consuming more dihydroxyacetone phosphate.

B) The system would shift to the right, producing more dihydroxyacetone phosphate and glyceraldehyde 3-phosphate.

C) The system would shift to the left, producing more fructose 1,6-bisphosphate.

D) The system would shift to the right, consuming some glyceraldehyde 3-phosphate and producing more dihydroxyacetone phosphate.

49) Energy is the capacity to do work.

50) Ammonia (NH3) is synthesized by the reaction of nitrogen and hydrogen in the presence of an iron catalyst according to the equation below. Removing the iron catalyst would decrease the reaction rate. 

51) Breaking a chemical bond requires energy.

52) An endothermic reaction is one in which energy is absorbed and ΔH is negative (–).

53) Bond dissociation energies are always positive numbers.

54) Bond breaking is endothermic.

55) Exothermic reactions involve the formation of products having lower energy than the reactants.

56) The stronger the bond, the higher its bond dissociation energy.

57) Changes in potential energy occur in chemical reactions.

58) The energy of the reacting molecules affects whether a particular collision will lead to a chemical reaction.

59) The difference in energy between the reactants and the transition state is called the energy of activation, symbolized by Ea.

60) Reactions with high Ea are generally fast reactions.

61) In the energy diagram shown below, the ΔH of the reaction is labeled by D. 

62) Chemical reactions are considered favorable if the products have a higher energy than the reactants.

63) Activation energy is the minimum amount of energy necessary for a reaction to occur.

64) Increasing the concentration of the reactants in a chemical reaction increases the number of collisions, and the reaction rate increases.

65) Increasing the temperature of a reaction mixture usually results in a decrease in the reaction rate.

66) Enzymes are proteins that act as biological catalysts.

67) Once equilibrium is reached in a chemical reaction, reactants stop forming products.

68) The expression for the equilibrium constant, K, for the general reaction: a A + b B   c C + d D is .

69) When the equilibrium constant for a reaction is much less than one (K < 1), the concentration of the products is larger than the concentration of the reactants.

70) Le Châtelier's principle is a general rule used to explain the effect of a change in reaction conditions on equilibrium.

71) Consider the following reversible reaction at equilibrium: CO(g) + Cl2(g)   COCl2(g). If chlorine gas is added to the reaction vessel, the equilibrium will shift to the right.

72) Consider the following reversible reaction at equilibrium: CO(g) + Cl2(g)   COCl2(g). If chlorine gas is added to the reaction vessel, the concentration of carbon monoxide will decrease.

73) Consider the following reversible reaction at equilibrium: CO(g) + Cl2(g)   COCl2(g). If the pressure inside the reaction vessel is increased, the equilibrium will shift to the left.

74) Consider the following reversible reaction at equilibrium: C­6­H12O6 (aq) + 6 O2(g)  6 CO2(g) + 6 H2O(l).  If oxygen gas is removed from the reaction vessel, the equilibrium will shift to the right.

75) Consider the following reversible reaction at equilibrium: C­6­H12O6 (aq) + 6 O2(g)  6 CO2(g) + 6 H2O(l). If carbon dioxide gas is removed from the reaction vessel, the equilibrium will shift to the right.

76) Consider the following reversible reaction at equilibrium: 2 NO(g) + O2(g)  2 NO2(g).  If oxygen gas is added to the reaction vessel, the equilibrium will shift to the left.

77) Consider the following reversible reaction at equilibrium: 2 NO(g) + O2(g)  2 NO2(g). If the pressure inside the reaction vessel is increased, the equilibrium will shift to the right.

78) Consider the following reversible reaction at equilibrium: CO(g) + Cl2(g)   COCl2(g), where ΔH = –108.6 kJ. When the temperature of the reaction vessel decreases, the system responds by forming more COCl2.

79) The larger the K for a reaction, the faster the reaction.

80) A reversible reaction in which K = 9.65 × 10–14 contains a negligible amount of reactants at equilibrium.

81) Kinetic energy is the energy associated with movement; potential energy is the energy inherent in an object due to its position or composition.

82) A manufacturing company requires 157 kJ of energy to power one of its machines for a day. The reaction shown below would be able to provide a sufficient amount of energy for this purpose.

2 HgO(s) → 2 Hg(l) + O2(g) ΔH = 182 kJ

83) Consider the reaction: 2 C2H6(g) + 7 O2(g) → 4 CO2(g) + 6 H2O(g). Decreasing the concentration of C2H6(g) will decrease the reaction rate.

84) Consider the reaction: 2 C2H6(g) + 7 O2(g) → 4 CO2(g) + 6 H2O(g). Increasing the concentration of C2H6(g) will decrease the activation energy.

85) Consider the reversible reaction: CO(g) + Cl2(g)   COCl2(g). The reverse reaction is COCl2(g) → CO(g) + Cl2(g).

86) When the equilibrium constant for a reversible reaction is much greater than one (K > 1), the equilibrium is said to lie to the right.

87) Consider the reversible reaction: PCl3(g) + Cl2(g)  PCl5(g), where K = 0.5. Since K < 1, [PCl5] must be less than 1 M.

88) The equilibrium constant expression for the reversible reaction: CHCl3(g) + 3 HCl(g)   CH4(g) + 3 Cl2(g) is  .

89) A reversible reaction is said to have reached equilibrium when the concentrations of the reactants and products become equal.

90) In order to cause an endothermic equilibrium reaction to shift in a direction to form more products, the reaction must be heated.

91) In order to cause an endothermic equilibrium reaction to shift in a direction to form more reactants, the reaction must be heated.

92) When ΔH is negative, the bonds formed in the products are ________ than the bonds broken in the reactants.

93) Heat is absorbed in an ________ reaction.

94) In an ________ reaction, the products are lower in energy than the reactants.

95) In the energy diagram shown below, C labels the ________. 

96) As a general rule, a reaction rate ________ for each 10 °C the temperature is raised.

97) When reactants can come together and form products, and products can come together to re-form reactants, the reaction is called a ________ reaction.

98) When heat is added to an exothermic equilibrium reaction, the reaction shifts to form more ________.

99) An enzyme contains a region called its ________ that binds a reactant, which then undergoes a very specific reaction with an enhanced rate.

100) Biological catalysts held together in a very specific three-dimensional shape are called ________.

101) The enzyme lactase aids in the digestion of ________.

102) The ΔH for the reaction depicted by the energy diagram below is ________.