Deck 6: Energy Changes, Reaction Rates, and Equilibrium

Question 1

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

Answer 1

B

Question 2

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

A)A labels the E_a of the reaction and B labels $\Delta$ H of the reaction.
B)A labels the $\Delta$ H of the reaction and B labels E_a of the reaction.
C)C labels the activation energy.
D)D labels the reactants and E labels the products.

Answer 2

A labels the E_a of the reaction and B labels $\Delta$ H of the reaction.

Question 3

In the reaction: 2 C₂H₆(g)+ 7 O₂(g) $\rightarrow$ 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 $\Delta$ H of the reaction.
D)increase the reaction rate.
E)decrease the reaction rate.

Answer 3

increase the reaction rate.

Question 4

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.

Question 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

Question 6

Consider the reaction, C₂H₄(g)+ H₂(g) $\rightarrow$ C₂H₆(g), where $\Delta$ H = -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

Question 7

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

Question 8

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

Question 9

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

Question 10

Which bond is the weakest?

A)H-Br
B)H-Cl
C)H-F
D)H-I

Question 11

Consider the reaction, C₂H₄(g)+ H₂(g) $\rightarrow$ C₂H₆(g), where $\Delta$ H = -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

Question 12

Which bond is the strongest?

A)H-Br
B)H-Cl
C)H-F
D)H-I

Question 13

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.

Question 14

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

Question 15

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.

Question 16

Consider the reaction: C₃H₈(g)+ 5 O₂(g) $\rightarrow$ 3 CO₂(g)+ 4 H₂O(g), where $\Delta$ H = -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.

Question 17

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

Question 18

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

Question 19

Consider the reaction, 3 NO₂(g)+ H₂O(l) $\rightarrow$ 2 HNO₃(aq)+ NO(g), where $\Delta$ H = -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

Question 20

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.

Question 21

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) $\Delta$ H= -25kJ
D)The reaction is favorable.

Question 22

Consider the combustion reaction of propane: C₃H₈(g)+ 5 O₂(g) $\rightarrow$ 3 CO₂(g)+ 4 H₂O(g), where $\Delta$ H = -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

Question 23

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

Question 24

Consider the reaction: C₃H₈(g)+ 5 O₂(g) $\rightarrow$ 3 CO₂(g)+ 4 H₂O(g), where $\Delta$ H = -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

Question 25

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

Question 26

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

Question 27

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

Question 28

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

Question 29

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

Question 30

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

Question 31

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.

Question 32

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

Question 33

The rusting of iron is described by the reaction: 4 Fe(s)+ 3 O₂(g) $\rightarrow$ 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.

Question 34

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.

Question 35

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.

Question 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 the above changes will increase the rate of a reaction.

Question 37

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.

Question 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 $\Delta$ H of a chemical reaction.
D)A catalyst is recovered unchanged in the reaction it catalyzes.

Question 39

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

Question 40

Consider the combustion reaction of propane: C₃H₈(g)+ 5 O₂(g) $\rightarrow$ 3 CO₂(g)+ 4 H₂O(g), where $\Delta$ H = -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

Question 41

In the energy diagram shown below, the $\Delta$ H of the reaction is labeled by D.

Question 42

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

Question 43

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

Question 44

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.

Question 45

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.

Question 46

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

Question 47

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

Question 48

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

Question 49

Breaking a chemical bond requires energy.

Question 50

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.

Question 51

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

Question 52

Changes in potential energy occur in chemical reactions.

Question 53

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.

Question 54

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

Question 55

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

Question 56

Reactions with high E_a are generally fast reactions.

Question 57

Energy is the capacity to do work.

Question 58

An endothermic reaction is one in which energy is absorbed and $\Delta$ H is negative (-).

Question 59

Bond breaking is endothermic.

Question 60

Bond dissociation energies are always positive numbers.

Question 61

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

Question 62

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

Question 63

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

Question 64

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.

Question 65

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

Question 66

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.

Question 67

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) $\rightarrow$ 2 Hg(l)+ O₂(g) $\Delta$ H = 182 kJ

Question 68

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

Question 69

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

Question 70

Consider the reversible reaction: CO(g)+ Cl₂(g) COCl₂(g). The reverse reaction is COCl₂(g) $\rightarrow$ CO(g)+ Cl₂(g).

Question 71

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

Question 72

When $\Delta$ H is negative, the bonds formed in the products are _____ than the bonds broken in the reactants.

Question 73

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

Question 74

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

Question 75

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

Question 76

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.

Question 77

Consider the following reversible reaction at equilibrium: CO(g)+ Cl₂(g) COCl₂(g), where $\Delta$ H = -108.6 kJ. When the temperature of the reaction vessel decreases, the system responds by forming more COCl₂.

Question 78

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.

Question 79

Enzymes are proteins that act as biological catalysts.

Question 80

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