Deck 5: Thermochemistry: Energy Changes in Reactions

Question 1

If a mass of 100.0 g moves through a distance of 50.0 m with an acceleration of 25.0 m s^-2, how much work was necessary to move the mass? F = ma, where F is force, m is mass, and a is acceleration. (1 J = 1 kg m² s^-2)

A)125 kJ
B)12.5 kJ
C)125 J
D)12.5 J
E)2.5 J

Answer 1

125 J

Question 2

Energy that an object has by virtue of its motion is called ________

A)kinetic energy.
B)thermal energy.
C)potential energy.
D)orbital energy.
E)mechanical energy.

Answer 2

kinetic energy.

Question 3

According to Coulomb's law, which ionic compound A-D has the smallest electrostatic potential energy (i.e., closest to zero)? The size of the anion increases in the order F < Cl < Br < I.

A)NaF
B)NaCl
C)NaBr
D)NaI
E)All have the same potential energy because the anions all have -1 charges.

Answer 3

NaI

Question 4

The kinetic energy associated with the random motion of molecules is called ________

A)motional energy.
B)work.
C)heat.
D)microscopic energy.
E)thermal energy.

Question 5

Work is done when a force moves an object some distance. Newton defined force as mass times acceleration. Acceleration is the rate at which velocity changes. What are the units of work?

A)kg . m² . s^-2
B)kg . m² . s^-1
C)kg . m . s^-2
D)kg² . m² . s^-2
E)kg . m

Question 6

Work requires ________

A)a use of potential energy.
B)a release of kinetic energy.
C)that a force moves an object.
D)a change in temperature.
E)the application of a force.

Question 7

The capacity to do work is a definition of ________

A)heat.
B)thermochemistry.
C)work.
D)energy.
E)ambition.

Question 8

What is the kinetic energy of a skier weighing 175 lb traveling 60 mph? (2.205 lb = 1 kg, 1 mi = 1.609 km, 1 J = 1 kg m²s^-2)

A)29 kJ
B)57 kJ
C)2.1 kJ
D)1.1 kJ
E)130 kJ

Question 9

Assuming that the distances between the two ions are the same in all cases, which of the following ion pairs has the smallest electrostatic potential energy (i.e., smallest in magnitude)?

A)
B)
C)
D)
E)

Question 10

Heat is best defined as ________

A)a substance that increases the temperature and causes water to boil.
B)a form of potential energy.
C)a form of work.
D)the total energy that a substance has.
E)energy transferred as the result of a temperature difference.

Question 11

Assuming that the distance between ions remains constant in all cases, which of the following ion pairs has the greatest electrostatic potential energy (i.e., largest in magnitude)?

A)
B)
C)
D)
E)

Question 12

Assuming that the charge of the ions remain constant in all cases, which of the following ion pairs has the greatest electrostatic potential energy (i.e., largest in magnitude)?

A)
B)
C)
D)
E)

Question 13

A diver jumps off a diving board. At which point in the diagram below will the diver possess the greatest potential energy?

A)A
B)B
C)C
D)D
E)E

Question 14

According to Coulomb's law, which ionic compound A-D has the largest electrostatic potential energy (i.e., largest in magnitude)?

A)NaCl
B)CaCl₂
C)AlCl₃
D)CoCl₂
E)All have the same potential energy because the chloride anions all have -1 charges.

Question 15

Which statement A-D about a state function is not correct?

A)The value of a state function can change along a path.
B)The final value of a state function is independent of the path taken to reach the final state.
C)All forms of energy must be state functions because energy is conserved in any process.
D)Examples of state functions only occur in chemistry and physics and not in real life.
E)Statements A-D all are correct.

Question 16

Thermochemistry is the study of how ________ is produced and consumed during chemical reactions.

A)kinetic energy
B)temperature
C)energy
D)work
E)potential energy

Question 17

Energy that an object has by virtue of its position is called ________

A)kinetic energy.
B)thermal energy.
C)potential energy.
D)heat.
E)mechanical energy.

Question 18

A diver jumps off a diving board. At which point in the diagram below will the diver possess the greatest kinetic energy?

A)A
B)B
C)C
D)D
E)E

Question 19

Which statement A-D about the relationship between energy and work is not correct?

A)It takes energy to do work.
B)When work is done, the energy of something must increase.
C)When a force moves an object some distance, the energy of the object increases.
D)When water turns a waterwheel, work is done and the energy of the water decreases.
E)Statements A-D all are correct.

Question 20

Assuming that the distances between the two ions are the same in all cases, which of the following ion pairs has the greatest electrostatic potential energy (i.e., largest in magnitude)?

A)
B)
C)
D)
E)

Question 21

Which arrow in the following diagrams represents an exothermic phase transition?

A)I and II only
B)II only
C)I, II, and IV only
D)III only
E)All represent endothermic transitions.

Question 22

Internal energy is defined as ________

A)the total kinetic energy of all the system components.
B)the total potential energy of all the system components.
C)the total of the potential and kinetic energies of all the system components.
D)the total potential energy minus the total kinetic energy of all the system components.
E)the total kinetic energy minus the total potential energy of all the system components.

Question 23

Which of the following bar charts shows the correct internal energy changes that occur in a pitcher of iced tea (system), the refrigerator (surroundings), and the universe as the iced tea in the refrigerator cools?

A)
B)
C)
D)

Question 24

What is the change in internal energy ( $\Delta$ E) when a system is heated with 35 J of energy while it does 15 J of work?

A)(+50 J)
B)(+20 J)
C)(-20 J)
D)(-50 J)
E)(+35 K)

Question 25

Which of the changes A-D will always increase the internal energy of a system?

A)The system gains energy and performs work.
B)The system gains energy and work is performed on it.
C)The system loses energy and performs work.
D)The system loses energy and work is performed on it.
E)None of the changes A-D will always increase the internal energy of a system.

Question 26

The first law of thermodynamics implies that ________

A)energy is transferred from the surroundings to the system during a combustion reaction.
B)if a system loses energy to the surroundings, then the surroundings must do an equal amount of work on the system.
C)if the surroundings gain energy from the system, then the system must lose an equal amount of energy.
D)energy is transferred from the system to the surroundings during a combustion reaction.
E)if a system does work on the surroundings, then the surroundings must transfer an equal amount of energy to the system.

Question 27

When solid sodium hydroxide (NaOH) pellets are dissolved in water, the temperature of the water and beaker rises. This is an example of ________

A)an exothermic process.
B)an endothermic process.
C)a combustion reaction.
D)a thermodynamic cycle.
E)all solvation processes.

Question 28

Which statement A-D about a system and its surroundings is not correct?

A)A capped thermos bottle is an example of an isolated system.
B)A metal box on a table is an example of a closed system.
C)A cup of coffee is an example of an open system.
D)No matter or energy can be exchanged between the surroundings and a closed system.
E)Statements A-D all are correct.

Question 29

During a(n) ________ process, energy is transferred from the system to the surroundings.

A)exothermic
B)endothermic
C)thermodynamic
D)thermochemical
E)physical

Question 30

Which of the following is an endothermic process for the system? In each case, the "system" is underlined.

A)a block of cheese being cooled in a refrigerator
B)a hot pack being used to warm a sore muscle
C)a heat pump being used to warm a house
D)a candle burning at a dinner table
E)ice cubes freezing in the refrigerator

Question 31

If a chemical reaction causes the temperature of the container to drop, it is a(n) ________ reaction.

A)endothermic
B)exothermic
C)spontaneous
D)fast
E)slow

Question 32

During a(n) ________ process, energy is transferred to the system from the surroundings.

A)exothermic
B)endothermic
C)thermodynamic
D)thermochemical
E)physical

Question 33

Which statement A-D about the first law of thermodynamics is not correct?

A)( is the change in the internal energy of a system.)
B)q is the energy added to or removed from the system.
C)q usually is called heat.
D)w is the energy added to or removed from the system by a deformation; that is, a force moves something.
E)The statements A-D are all correct.

Question 34

Which one of the following statements is not correct?

A)When dry ice sublimes to form CO₂(g), the internal energy of the surroundings decreases.
B)In any physical process, such as dew forming on grass or carbon dioxide subliming, the internal energy of the system does not change.
C)When dew forms on grass overnight, the energy of the water molecules decreases.
D)When dew forms on grass overnight, the energy of the surroundings (grass, air, etc.) increases.
E)When dry ice sublimes to form CO₂(g), the energy of the carbon dioxide increases.

Question 35

A student dissolving some ammonium nitrate (NH₄NO₃) in water notices that the beaker gets cooler as the solid dissolves. This is an example of ________

A)an exothermic process.
B)an endothermic process.
C)a combustion reaction.
D)a thermodynamic cycle.
E)all solvation processes.

Question 36

The following diagrams illustrate the flow of energy (q) and work (w) in different processes. Which one is definitely not an endothermic process?

A)
B)
C)
D)
E)

Question 37

Which arrow in the following diagrams represents an endothermic phase transition?

A)I and II only
B)I and III only
C)II and IV only
D)III and IV only
E)All represent exothermic transitions.

Question 38

The following diagrams illustrate the flow of energy (q) and work (w) in different processes. Which one is definitely an exothermic process?

A)
B)
C)
D)

Question 39

According to the first law of thermodynamics, which of the changes A-D will always increase the internal energy of a system? (q = energy transferred, and w = work done)

A)q > 0, w < 0
B)q > 0, w > 0
C)q < 0, w < 0
D)q < 0, w > 0
E)None of the changes A-D will always increase the internal energy of a system.

Question 40

Which of the following bar charts shows the correct internal energy changes that occur when a propane grill is used to cook a steak? (Consider the propane combustion reaction to be the system. Consider the grill, steak, and everything else to be the surroundings.)

A)
B)
C)
D)

Question 41

A cooling curve for some substance is shown below. Which of the line segments (I-V) represents cooling of the gas?

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

Question 42

The change in enthalpy and the change in internal energy of a system always will be equal when ________

A)the process is exothermic.
B)the process is endothermic.
C)the process is isothermal.
D)the pressure is constant.
E)the volume is constant.

Question 43

Which statement A-D about the first law of thermodynamics is not correct?

A)q is the energy added to or removed from the system by a temperature difference.
B)w is the energy added to or removed from the system by a deformation; that is, a force moves something.
C)If the only work that is done is P-V work, then q = the change in enthalpy.
D)( $\Delta$ E_system is the change in the Gibbs free energy of the system.)
E)The statements A-D are all correct.

Question 44

A cooling curve for some substance is shown below. Which of the line segments (I-V) represents the liquid-to-solid transition?

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

Question 45

You heat a cup of coffee in a microwave oven. It absorbs 40 kJ of energy from the microwave, and the volume expands. Which one of the following statements correctly describes the relationship between the change in enthalpy $\Delta$ H and the change in internal energy $\Delta$ E of the coffee? (> means greater than, < means less than)

A)( $\Delta$ H 40 kJ, $\Delta$ E 40 kJ)
B)( $\Delta$ H 40 kJ, $\Delta$ E 40 kJ)
C)( $\Delta$ H 40 kJ, $\Delta$ E 40 kJ)
D)( $\Delta$ H 40 kJ, $\Delta$ E 40 kJ)
E)( $\Delta$ H 40 kJ, $\Delta$ E 40 kJ)

Question 46

Which statement below regarding the various heat capacities is not correct?

A)A heterogeneous object cannot be characterized by a specific heat capacity.
B)The molar heat capacity of a substance always is larger than the specific heat capacity of the substance.
C)The heat capacity of an object depends on the mass of the object.
D)The specific heat capacity of an object does not depend on the mass of the object.
E)The difference between the specific heat capacity and heat capacity of an object does not depend on the mass of the object.

Question 47

How much work does a gas do when it expands against a constant pressure of 0.500 atm from a volume of 50.00 mL to a volume of 350.00 mL? (101.3 J = 1 L atm)

A)15.2 J
B)0.150 J
C)(-15.2 J)
D)(-0.152 J)

Question 48

The best definition of the enthalpy change is ________

A)the energy that is transferred into or out of a system because of a temperature difference when the pressure is constant and only PV work is done.
B)the change in internal energy of a system when the pressure is constant.
C)the change in internal energy of a system when the volume is constant.
D)the energy that is transferred into or out of a system when the pressure is constant and no work is done.
E)the change in internal energy of a system when the pressure is constant and no work is done.

Question 49

In a steam engine, steam in a cylinder expands against a piston, exerting 10 atm of external pressure. The volume of the cylinder increases by 10 L and simultaneously the steam cools, losing 3,000 kJ of energy to the surroundings. What is the change in energy of the steam? (101.3 J = 1 L atm)

A)(-3,010 kJ)
B)(-3,001 kJ)
C)(-3,100 kJ)
D)(-13,135 kJ)
E)(-2,990 kJ)

Question 50

What is the heat capacity (C_p) of a 7.5 g piece of tin if its temperature changes by 12.3 ^$\circ$
C when it is supplied with 20 J from a Bunsen burner?

A)
B)
C)
D)
E)

Question 51

At a certain elevation, the boiling point of water is 98.5 . How much energy is needed to heat 35.0 mL of water to the boiling point at this elevation if the water initially was at 23.4 ^$\circ$
C? (C_P = 75.38 J/(mol · ), d = 1.00 g/mL)

A)8.5 kJ
B)11.0 kJ
C)0.93 kJ
D)1.0 kJ
E)25.6 kJ

Question 52

The heating curve for a substance is shown below. The substance initially is a solid. It then becomes a liquid and a gas. Which of the line segments (I-V) represents the solid-to-liquid phase transition?

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

Question 53

A pot of water is heated with 10 J of energy at constant pressure. What is the enthalpy change ( $\Delta$ H) for this process?

A)(-10 J)
B)(> 10 J)
C)(+10 J)
D)(< 10 J)
E)0

Question 54

Which statement A-D about energy units is not correct?

A)The SI unit of energy is the Joule (J).
B)In terms of SI base units, 1 J = 1 kg m² s^-2.
C)A nutritional calorie (1 Cal) is equal to 1,000 cal.
D)A nutritional calorie (1 Cal) is 4.184 kJ.
E)Statements A-D all are correct.

Question 55

What is the change in internal energy ( $\Delta$ E) of a system when it loses 10 kJ of energy and 5,000 J of work is done on the system?

A)(+15 kJ)
B)(-10 kJ)
C)(-5 kJ)
D)(+5,010 J)
E)(+4,990 J)

Question 56

What will be the final temperature of a 10.0 g piece of iron (C_P =25.09 J/(mol · ) initially at 25 ^$\circ$
C, if it is supplied with 9.5 J from a stove?

A)
B)
C)
D)
E)

Question 57

During an exothermic process, ________ for the system.

A)q > 0
B)w > 0
C)( $\Delta$ H > 0)
D)( $\Delta$ H < 0)
E)q + w = 0

Question 58

An expanding gas does 175 kJ of work on its surroundings at a constant pressure of 5.55 atm. If the gas initially occupied 125 mL, what is the final volume of the gas? (101.3 J = 1 L atm)

A)31.5 L
B)31,500 mL
C)311 mL
D)311 L
E)31,500 L

Question 59

A heating curve for some substance is shown below. Which of the line segments (I-V) represents heating of the liquid?

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

Question 60

Steam in a cylinder is compressed by a piston exerting a constant pressure of 5 atm. The volume of the cylinder decreases by 15 L and simultaneously the steam is cooled, losing 105 kJ of energy as heat. How much energy, total, was gained or lost by the steam in this process? (101.3 J = 1 L atm)

A)(-30.0 kJ)
B)(-97.4 kJ)
C)(-113 kJ)
D)(-180.0 kJ)
E)113 kJ

Question 61

In an experiment, 30.0 g of metal was heated to 98.0 ^$\circ$ C and then quickly transferred to 50.0 g of water in a calorimeter. The heat capacity of the calorimeter with the water was 211 J/ ^$\circ$ C. The initial temperature of the calorimeter was 27.0 ^$\circ$ C, and the final temperature after addition of the metal was 32.5 ^$\circ$ C. What is the value of the specific heat capacity of the metal?

A)0.140 J/(g . ^$\circ$ C)
B)83.0 J/(g . ^$\circ$ C)
C)0.540 J/(g . ^$\circ$ C)
D)0.591 J/(g . ^$\circ$ C)
E)29.5 J/(g . ^$\circ$ C)

Question 62

If 7.3 kJ of energy are required to change the temperature of water from 5.0 to 70.0 , what was the volume of water? (c_s = 4.184 J/(g . ), d = 1.00 g/mL)

A)27 mL
B)37 mL
C)110 mL
D)0.73 mL
E)75 mL

Question 63

Ammonium nitrate sometimes is used in cold packs because its enthalpy of solvation in water is +21 kJ/mol. What is the minimum amount of ammonium nitrate (80.05 g/mol) that is needed to cool a 1.0 L soft drink (d = 1.0 g/mL, specific heat 4.5 J g^-1 ) and its plastic bottle (heat capacity 50 J/K) from 30 to 5 .

A)540 g
B)320 g
C)110 g
D)430 g
E)250 g

Question 64

Which of the following objects will cool the fastest from the same initial temperature, assuming you had equal masses of each?

A)an aluminum pan (c_s = 0.90 J/(g . ))
B)a copper pot (c_s = 0.39 J/(g . ))
C)an iron skillet (c_s = 0.45 J/(g . ))
D)a container of water (4.2 J/(g . ))
E)a container of ethanol (2.5 J/(g . ))

Question 65

Given the following thermochemical equation detailing the combustion of methane CH₄(g) 2O₂(g) CO₂(g) 2H₂O(g) $\Delta$ H_rxn = -802kJ/mol CH₄
Determine the amount of energy released when 25.0 g of methane undergoes combustion.

A)1.95 kJ
B)3.12 kJ
C)453 kJ
D)1250 kJ
E)2.01 kJ

Question 66

When 1.14 g of octane (molar mass = 114 g/mol) reacts with excess oxygen in a constant volume calorimeter, the temperature of the calorimeter increases by 10.0 ^$\circ$ C. The heat capacity of the calorimeter is 6.97 kJ/ ^$\circ$ C. Determine the energy flow, q (reaction).

A)(+69.7 kJ)
B)(+6,970 kJ)
C)(-69.7 kJ)
D)(-6,970 kJ)
E)(+6.97 kJ)

Question 67

A 15 g piece of iron (C_P = 25.09 J/(mol · ^$\circ$ C)) is heated to a temperature of 95 ^$\circ$ C and placed into a bucket containing 4.5 gal of water (C_P = 75.38 J/(mol · ^$\circ$ C)) initially at 25 ^$\circ$ C. Eventually, ________

A)the water will be warmer than the iron.
B)the iron will be warmer than the water.
C)the iron will be colder than the water.
D)the iron and the water will be at the same temperature.
E)the temperature will be the average of 95 ^$\circ$ C and 25 ^$\circ$ C.

Question 68

Given the following thermochemical equation detailing the combustion of glucose C₆H₁₂O₆(s) 6O₂(g) CO₂(g) 6H₂O(g) $\Delta$ H_rxn = -2803 kJ/mol C_6-H₁₂O₆
Determine the amount of glucose needed to release 30 kJ of energy.

A)11.58 g
B)1.93 g
C)467 g
D)1,930 g
E)5.35 g

Question 69

When 2.50 g of sucrose (molar mass = 342.30 g/mol) reacts with excess oxygen in a constant volume calorimeter, the temperature of the calorimeter increases by 9.17 ^$\circ$ C. The heat capacity of the calorimeter is 4.90 kJ/ ^$\circ$ C. Determine the heat of combustion per mole of sucrose.

A)(-44.9 kJ/mol)
B)(+44.9 kJ/mol)
C)(+1,030 kJ/mol)
D)(-6,150 kJ/mol)
E)(+6,150 kJ/mol)

Question 70

The cooling system in an automobile holds 10.0 L of ethylene glycol antifreeze. How much energy is absorbed when the temperature of the ethylene glycol goes from 20 to 100 ? The density and specific heat capacity of ethylene glycol are 1.11 g/mL and 2.42 J/(g . ), respectively.

A)2,150 J
B)2,150 kJ
C)1,940 kJ
D)1,940 J
E)215 J

Question 71

In an experiment, 5.0 g of ice at -12 is converted into steam with a temperature of 120 . How much energy is required for this process? V_vap = 2,260 J/g; H_fus = 334 J/g; c_s(ice)= 2.06 J/(g . ); c_s(water) = 4.18 J/(g . ); c_s(steam) =1.99 J/(g . ))

A)11.3 kJ
B)2.09 kJ
C)0.199 kJ
D)15.4 kJ
E)30.8 kJ

Question 72

A 150 g piece of iron (C_P = 25.09 J/(mol . )) was heated to a temperature of 47 and then placed in contact with a 275 g piece of copper at 20 (C_P = 25.46 J/(mol . )). What was the final temperature of the two pieces of metal?

A)25
B)20
C)30
D)47
E)33

Question 73

In an experiment, 10.0 g of ice at -20 ^$\circ$ C is converted into steam with a temperature of 110 . How much energy is required for this process? ^$\circ$
_vap 2,260 J/g; H_fus = 334 J/g; c_s(ice) = 2.06 J/(g . ); c_s(water) = 4.18 J/(g . ); c_s(steam) = 1.99 J/(g . ))

A)30.7 kJ
B)26.8 kJ
C)34.9 kJ
D)30.3 kJ
E)38.7 kJ

Question 74

The energy content of a Big Mac is 540 Cal. How much water can be heated from 20 to 90 by this amount of energy? (c_P(water) = 1.00 g/mL, c_s(water) = 4.18 J/(g . ), 1 Cal = 1,000 cal = 4.184 kJ)

A)2.2 mL
B)6.0 L
C)7.7 mL
D)7.7 L
E)6.0 mL

Question 75

You hold a 50 g sphere of copper in one hand and a 25 g sphere of aluminum in the other hand. If both absorb energy at the same rate, which will come to your body temperature first and why? The specific heat capacities are 0.4 J/(g . ) for copper and 0.9 J/(g . ) for aluminum.

A)copper, because the specific heat is smaller
B)aluminum, because the specific heat is larger
C)aluminum, because the mass is smaller
D)copper, because the heat capacity is smaller
E)Both reach body temperature at the same time because they absorb energy at the same rate.

Question 76

A food sample was burned in a bomb calorimeter containing 524 mL water. How much thermal energy was produced when the temperature of the water and the calorimeter rose from 20.0 ^$\circ$ C to 25.0 ^$\circ$ C? The metal calorimeter had a heat capacity of 725 J/ ^$\circ$ C without the water. The specific heat capacity of water is 4.184 J/(g ^$\circ$ C).

A)3.63 kJ
B)14.6 kJ
C)58.4 kJ
D)45.8 kJ
E)46.1 kJ

Question 77

You have a summer job in a lead foundry. Your task is to identify how energy efficiency can be improved. You therefore need to know the minimum amount of energy it takes to raise 1 pound of lead (454 g) from room temperature (25 ) to its melting point (327 ) and then melt it. The specific heat capacity of lead is 0.159 J/(g . ), the enthalpy of fusion is 24.7 J/g, and the molar mass is 207 g/mol.

A)3.39 MJ
B)21.9 kJ
C)21.0 kJ
D)33.0 kJ
E)11.0 kJ

Question 78

In an experiment, 74.3 g of metallic copper was heated to 100.0 ^$\circ$ C and then quickly dropped into 200.0 mL of water in a calorimeter. The heat capacity of the calorimeter with the water was 875 J/ ^$\circ$ C. The initial temperature of the calorimeter was 27.5 ^$\circ$ C, and the final temperature after addition of the metal was 29.8 ^$\circ$ C. What is the value of the molar heat capacity of copper?

A)4.18 J/(mol . ^$\circ$ C)
B)8.17 J/(mol . ^$\circ$ C)
C)49.0 J/(mol . ^$\circ$ C)
D)12.3 J/(mol . ^$\circ$ C)
E)24.5 J/(mol . ^$\circ$ C)

Question 79

Using the following data for water, determine the final temperature when 100 g of ice at -10 is heated with 350 kJ of energy.

A)309
B)100
C)382
D)225
E)325

Question 80

In an experiment, 7.5 g of liquid water at 35 is converted into steam with a temperature of 145 ^$\circ$
C. How much energy is required for this process?( H_vap= 2,260 J/g; H_fus = 334 J/g; c_s(ice) = 2.06 J/(g . ); c_s(water) = 4.18 J/(g . ); c_s(steam) = 1.99 J/(g . ))

A)2.04 kJ
B)17.0 kJ
C)19.7 kJ
D)5.40 kJ
E)125 kJ