Deck 5: Thermochemistry

Question 1

An endothermic reaction causes the surroundings to

A)warm up.
B)become acidic.
C)condense.
D)decrease in temperature.
E)release CO₂.

Answer 1

decrease in temperature.

Question 2

What law states that energy can be converted from one form to another,but cannot be created or destroyed?

A)universal law
B)first law of thermodynamics
C)law of mass conservation
D)law of conservation of energy
E)law of constant energy

Answer 2

first law of thermodynamics

Question 3

For the reaction: 2A + B₂ → 2AB ΔH = +50.0 kJ.

A)The reaction is endothermic.
B)Heat is released to the surroundings.
C)The standard enthalpy of formation for AB is 50.0 kJ.
D)The bond energy for each A-B bond is 50.0 kJ.
E)The molecule AB contains less energy than A or B₂.

Answer 3

The reaction is endothermic.

Question 4

A system contracts from an initial volume of 15.0 L to a final volume of 10.0 L under a constant external pressure of 0.80 atm.What is W? (1 L·atm = 101.3 J)

A)-4.0 J
B)+4.0 J
C)-4.1 ×10² J
D)+4.1 ×10² J
E)+81 J

Question 5

If two solutions are mixed together in a container and the container "feels hot",then

A)the reaction is endothermic.
B)the reaction is exothermic.
C)the energy of the universe is increased.
D)the energy of both the system and the surroundings is decreased.
E)the energy of the system is increased.

Question 6

Which of these is not a state function?

A)volume
B)temperature
C)pressure
D)heat
E)energy

Question 7

An exothermic reaction causes the surroundings to

A)warm up.
B)become acidic.
C)expand.
D)decrease its temperature.
E)release CO₂.

Question 8

Complete the sentence: When heat is transferred to the system,the process is said to be ____________,and the sign of q is __________.

A)exothermic,positive
B)exothermic,negative
C)endothermic,positive
D)endothermic,negative
E)forbidden,indeterminate

Question 9

Which type of system may transfer energy,but not mass,to the surroundings?

A)mass transfer system
B)isolated system
C)closed system
D)nonenergy system
E)open system

Question 10

A system which does work on the surroundings with no heat change has

A)w < 0,ΔU = 0.
B)W > 0,ΔU > 0.
C)W > 0,ΔU < 0.
D)W < 0,ΔU > 0.
E)W < 0,ΔU < 0.

Question 11

How many calories are in 854.3 J? (1 cal = 4.184 J)

A)4.897 × 10^-3 cal
B)204.2 cal
C)1.171 ×10^-3 cal
D)0.2390 cal
E)3574 cal

Question 12

How many joules are in 1.20 ×10³ calories? (1 cal = 4.184 J)

A)8.33 × 10^-4 J
B)3.49 × 10^-3 J
C)2.39 × 10^-1 J
D)2.86 × 10² J
E)5.02 × 10³ J

Question 13

A system that does no work but which transfers heat to the surroundings has

A)q < 0,ΔU > 0.
B)q < 0,ΔU < 0.
C)q > 0,ΔU > 0.
D)q > 0,ΔU < 0.
E)q < 0,ΔU = 0.

Question 14

Which relationship is always correct?

A)potential energy + kinetic energy = constant
B)Δ = q + W
C)ΔU = ΔH - PΔV
D)H = U + PV
E)ΔH = q V

Question 15

An ideal gas (the system)is contained in a flexible balloon at a pressure of 1 atm and is initially at a temperature of 20.°C.The surrounding air is at the same pressure,but its temperature is 25°C.When the system has equilibrated with its surroundings,both system and surroundings are at 25°C and 1 atm.In changing from the initial to the final state,which one of the following relationships regarding the system is correct?

A)ΔU < 0
B)ΔU = 0
C)ΔH = 0
D)W > 0
E)q > 0

Question 16

A system which does work on the surroundings with no heat change has

A)W = ΔU.
B)W = -ΔU.
C)W > 0,ΔU < 0.
D)W < 0,ΔU > 0.
E)W > ΔU.

Question 17

A system that does no work but which receives heat from the surroundings has

A)q < 0,ΔU > 0.
B)q > 0,ΔU < 0.
C)q = ΔU.
D)q = -ΔU.
E)w = ΔU.

Question 18

What is the change in internal energy in joules for a system that releases 154 J of heat and does 125 J of work on its surroundings?

A)-29 J
B)279 J
C)29 J
D)1.23 J
E)-279 J

Question 19

When heat is absorbed by the system and work is done by the system on the surroundings then

A)q is negative and w is positive.
B)both q and w are positive.
C)both q and w are negative.
D)q is positive and w is negative.
E)both q and W are zero.

Question 20

A system expands from a volume of 1.00 L to 2.00 L against a constant external pressure of 1.00 atm.What is the work (W)done by the system? (1 L·atm = 101.3 J)

A)1.00 J
B)2.00 J
C)1.01 × 10² J
D)1.01 × 10⁵ J
E)3.00 J

Question 21

What is the equation for the formation reaction for gaseous hydrazine,N₂H₄,at 25ºC and 1 atm pressure?

A)2N₂H₄(g)→ 2NH₃(g)+ H₂(g)
B)2NH₃(g)+ H₂(g)→ N₂H₄(g)
C)N₂(g)+ 2H₂O(g)→ N₂H₄(g)+ O₂(g)
D)N₂(g)+2H₂(g)→ N₂H₄(g)
E)2NO₂(g)+ 6H₂(g)→ N₂H₄(g)+ 4H₂O(g)

Question 22

Which is not a state function?

A)internal energy
B)volume
C)work
D)pressure
E)enthalpy

Question 23

A system delivers 1275 J of heat while the surroundings perform 854 J of work on it.What is ΔU of the system?

A)-2129 J
B)-421 J
C)+421 J
D)+2129 J
E)-1275 J

Question 24

For which reaction is ΔH approximately (or exactly)equal to ΔU?

A)H₂(g)+ Br₂(g)→ 2HBr(g)
B)H₂O(l)→ H₂O(g)
C)CaCO₃(s)→ CaO(s)+ CO₂(g)
D)2H(g)+ O(g)→ H₂O(l)
E)CH₄(g)+ 2O₂(g)→ CO₂(g)+ 2H₂O(l)

Question 25

Two solutions (the system),each with a volume of 25.0 mL at 25.0°C,are mixed in a beaker.A reaction occurs between them,and the temperature rises to 35.0°C.After the products have equilibrated with the surroundings,the temperature is again 25.0°C and the total volume is 50.0 mL.No gases are involved in the reaction.Which relationship concerning the change from initial to final states (both at 25.0°C)is correct?

A)ΔU = 0
B)ΔH = 0
C)ΔU > 0
D)q = 0
E)W = 0

Question 26

The dissolution of barium hydroxide in water is an exothermic process.Which statement is correct?

A)The enthalpy of solid barium hydroxide plus pure water is less than that of the solution,at the same temperature.
B)The enthalpy of solid barium hydroxide plus pure water is greater than that of the solution,at the same temperature.
C)The enthalpy of solid barium hydroxide plus pure water is the same as that of the solution,at the same temperature.
D)The temperature of the solution is lower than of the barium hydroxide and water before mixing.
E)When barium hydroxide dissolves in water,the system does work on the surroundings.

Question 27

A Snickers candy bar contains 280 Calories,of which the fat content accounts for 120 Calories.What is the energy of the fat content,in kJ? (1 cal = 4.184 J)

A)5.0 × 10^-1 kJ
B)1.2 kJ
C)5.0 × 10² kJ
D)1.2 × 10³ kJ
E)1.6 × 10³ kJ

Question 28

What is q if 28.6 g of water is heated from 22.0°C to 78.3°C? The specific heat of water is 4.184 J/g·°C.

A)2.60 J
B)2.63 kJ
C)6.74 kJ
D)9.37 kJ
E)3.94×10⁴ kJ

Question 29

A system delivers 222 J of heat to the surroundings while delivering 645 J of work.What is the change in the internal energy,ΔU,of the system?

A)-423 J
B)+423 J
C)-867 J
D)+867 J
E)-222 J

Question 30

Your favorite candy bar,Gummy Beakers,contains 1.2 × 10⁶ J of energy while your favorite soft drink,Bolt,contains 6.7 × 10⁵ J.If you eat two packs of Gummy Beakers a day and drink 3 cans of Bolt,what percent of your 2000 Calorie daily food intake is left for broccoli,beans,beef,etc.? (1 cal = 4.184 J)

A)53%
B)47%
C)27%
D)11%
E)0%

Question 31

The specific heat (capacity)is

A)amount of energy needed to change 1 g of a substance by 1°C.
B)amount of energy needed to change 1 mol of a substance by 1°C.
C)amount of energy required to melt 1 g of substance.
D)amount of substance that is heated by 1°C.
E)the temperature increase,in K,associated with heating 1 g of a substance for 1 minute.

Question 32

For a particular process,28 kJ of heat is absorbed and 15 kJ of work is done on the surroundings.What is ΔU?

A)ΔU = +43 kJ
B)ΔU = -43 kJ
C)ΔU = -13 kJ
D)ΔU = +13 kJ
E)ΔU = +28 kJ

Question 33

A system receives 575 J of heat and delivers 424 J of work.What is the change in the internal energy,ΔU,of the system?

A)-150.J
B)150.J
C)-1000.J
D)1000.J
E)575 J

Question 34

In which process is ΔH = ΔU?

A)Two moles of ammonia gas are cooled from 325°C to 300°C at a constant pressure of 1.2 atm.
B)One gram of water is vaporized at 100°C and 1 atm.
C)Two moles of hydrogen iodide gas react to form hydrogen gas and iodine gas in a 40-L container.
D)Solid calcium carbonate is heated to form solid calcium oxide and carbon dioxide gas in a container with variable volume.
E)One mole of solid carbon dioxide sublimes to the gas phase.

Question 35

A system absorbs 21.6 kJ of heat while performing 6.9 kJ of work on the surroundings.If the initial internal energy,U,is 61.2 kJ,what is the final value of U?

A)32.7 kJ
B)46.5 kJ
C)61.2 kJ
D)75.9 kJ
E)89.7 kJ

Question 36

Ethylene glycol,used as a coolant in automotive engines,has a specific heat capacity of 2.42 J/g°C.Calculate q when 3.65 kg of ethylene glycol is cooled from 132°C to 85°C.

A)-1900 kJ
B)-420 kJ
C)-99 kJ
D)-0.42 kJ
E)-4.2 × 10^-6 kJ

Question 37

Natural gas,or methane,is an important fuel.Combustion of one mole of methane releases 802.3 kJ of energy.How much energy does that represent in kcal? (1 cal = 4.184 J)

A)1.92 × 10^-1 kcal
B)1.92 × 10² kcal
C)3.36 × 10³ kcal
D)1.92 × 10⁵ kcal
E)3.36 × 10⁶ kcal

Question 38

In which reaction would you expect ΔH to be substantially greater than ΔU (i.e.,ΔH > ΔU)?

A)H₂(g)+ Br₂(g)→ 2HBr(g)
B)CO₂(s)→ CO₂(g)
C)C₂H₂(g)+ H₂(g)→ C₂H₄(g)
D)H₂O(s)→ H₂O(l)
E)HCl(aq)+ NaOH(aq)→ NaCl(aq)+ H₂O(l)

Question 39

A system initially has an internal energy U of 504 J.It undergoes a process during which it releases 111 J of heat energy to the surroundings,and does work of 222 J.What is the final energy of the system,in J?

A)171 J
B)393 J
C)504 J
D)615 J
E)837 J

Question 40

If,as a pioneer,you wished to warm your room by taking an object heated on top of a pot-bellied stove to it,which of the following 15-pound objects,each heated to 100°C,would be the best choice? The specific heat capacity (in J/g·°C)for each substance is given in parentheses.Iron (0.450),copper (0.387),granite (0.79),gold (0.129),water (4.184).

A)iron
B)copper
C)granite
D)gold
E)H₂O

Question 41

A common laboratory reaction is the neutralization of an acid with a base.When 50.0 mL of 0.500 M HCl at 25.0°C is added to 50.0 mL of 0.500 M NaOH at 25.0°C in a coffee cup calorimeter,the temperature of the mixture rises to 28.2°C.What is the heat of reaction per mole of acid? Assume the mixture has a specific heat capacity of 4.18 J/g·°C and that the densities of the reactant solutions are both 1.00 g/mL.

A)670 J
B)1300 J
C)27 kJ
D)54 kJ
E)> 100 kJ

Question 42

How much heat is required to raise the temperature of 22.8 g of copper from 20.0°C to 875.0°C? The specific heat of copper is 0.385 J/g·°C.

A)14.4 J
B)176 J
C)7.51 kJ
D)7.68 kJ
E)9.90 kJ

Question 43

When 0.7521 g of benzoic acid was burned in a calorimeter containing 1000.g of water,a temperature rise of 3.60°C was observed.What is the heat capacity of the bomb calorimeter,excluding the water? The heat of combustion of benzoic acid is -26.42 kJ/g.

A)15.9 kJ/°C
B)4.2 kJ/°C
C)5.5 kJ/°C
D)1.3 kJ/°C
E)752 kJ/°C

Question 44

Naphthalene combustion may be used to calibrate the heat capacity of a bomb calorimeter.The heat of combustion of naphthalene is -40.1 kJ/g.When 0.8210 g of naphthalene was burned in a bomb calorimeter containing 1.000 kg of water,a temperature rise of 4.21°C was observed.What is the heat capacity of the bomb calorimeter excluding the water?

A)32.9 kJ/°C
B)7.8 kJ/°C
C)3.64 kJ/°C
D)1.76 kJ/°C
E)15.3 kJ/°C

Question 45

When Karl Kaveman adds chilled grog to his new granite mug,he removes 10.9 kJ of energy from the mug.If it has a mass of 625 g and was at 25°C,what is its new temperature? Specific heat capacity of granite = 0.79 J/g·°C.

A)3°C
B)14°C
C)22°C
D)47°C
E)None of these choices is correct.

Question 46

What is the change in temperature if a 25.0-g block of aluminum absorbs 10.0 kJ of heat? The specific heat of aluminum is 0.900 J/g·°C.

A)0.44°C
B)22.5°C
C)225°C
D)360°C
E)444°C

Question 47

If 75.4 J of energy is absorbed by 0.25 mol of CCl₄ at constant pressure,what is the change in temperature? The specific heat of CCl4 is 0.861 J/g·°C.

A)17.8°C
B)21.9°C
C)2.3°C
D)9.1°C
E)44.6°C

Question 48

A 307-g sample of an unknown mineral was heated to 98.7°C and placed into a calorimeter containing 72.4 g of water at 23.6°C.The heat capacity of the calorimeter was 15.7 J/°C.The final temperature in the calorimeter was 32.4°C.What is the specific heat capacity of the mineral?

A)0.124 J/g·°C
B)0.131 J/g·°C
C)0.138 J/g·°C
D)0.145 J/g·°C
E)None of these choices is correct.

Question 49

The specific heat of gold is 0.129 J/g·°C.What is the molar heat capacity of gold?

A)0.0394 J/mol·°C
B)0.129 J/mol·°C
C)25.4 J/mol·°C
D)39.4 kJ/mol·°C
E)197 J/mol·°C

Question 50

The heat of solution of ammonium chloride is 15.2 kJ/mol.If a 6.134-g sample of NH₄Cl is added to 65.0 mL of water in a calorimeter at 24.5°C,what is the final temperature of the solution? The specific heat of water is 4.18 J/g·°C and the heat capacity of the calorimeter is 365 J/°C.

A)27.1°C
B)18.6°C
C)19.7°C
D)21.8°C
E)30.4°C

Question 51

A 275-g sample of nickel at l00.0°C is placed in 100.0 g of water at 22.0°C.What is the final temperature of the water? Assume no heat transfer with the surroundings.The specific heat of nickel is 0.444 J/g·°C and the specific heat of water is 4.184 J/g·°C.

A)39.6°C
B)40.8°C
C)61.0°C
D)79.2°C
E)82.4°C

Question 52

A piece of copper metal is initially at 100.0°C.It is dropped into a coffee cup calorimeter containing 50.0 g of water at a temperature of 20.0°C.After stirring,the final temperature of both copper and water is 25.0°C.Assuming no heat losses,and that the specific heat (capacity)of water is 4.18 J/g·°C,what is the heat capacity of the copper in J/°C?

A)2.79 J/°C
B)3.33 J/°C
C)13.9 J/°C
D)209 J/°C
E)None of these choices is correct.

Question 53

If 325 g of water at 4.2°C absorbs 12.28 kJ,what is the final temperature of the water? The specific heat of water is 4.184 J/g·°C.

A)4.21°C
B)4.8°C
C)9.0°C
D)13.2°C
E)2938°C

Question 54

Suppose a 50-g block of silver (specific heat = 0.2350 J/g·°C)at 100°C is placed in contact with a 50-g block of iron (specific heat = 0.4494 J/g·°C)at 0°C,and the two blocks are insulated from the rest of the universe.The final temperature of the two blocks

A)will be higher than 50°C.
B)will be lower than 50°C.
C)will be exactly 50°C.
D)is unrelated to the composition of the blocks.
E)cannot be predicted.

Question 55

Benzene is a starting material in the synthesis of nylon fibers and polystyrene (styrofoam).Its specific heat capacity is 1.74 J/g·°C.If 16.7 kJ of energy is absorbed by a 225-g sample of benzene at 20.0°C,what is its final temperature?

A)-22.7°C
B)37.7°C
C)42.7°C
D)62.7°C
E)80.1°C

Question 56

A glass containing 200.0 g of H₂O at 20.0°C was placed in a refrigerator.The water loses 11.7 kJ as it cools to a constant temperature.What is its new temperature? The specific heat of water is 4.184 J/g·°C.

A)0.0°C
B)4.0°C
C)6.0°C
D)14.0°C
E)34.0°C

Question 57

A 1.00-g sample of octane (C₈H₁₈)is burned in a bomb calorimeter that has a heat capacity of 5.80 kJ/°C.The temperature of the calorimeter rises from 25.00°C to 33.20°C.What is ΔU per mole for the combustion of octane?

A)-47.6 kJ/mol
B)-416 kJ/mol
C)-707 kJ/mol
D)-5.43 ×10³ kJ/mol
E)-1.86 ×10⁵ kJ/mol

Question 58

How much heat is required to raise the temperature of 1500 g of water from 25°C to 52°C? The specific heat of water is 4.184 J/g·°C.

A)1500 kJ
B)170 kJ
C)6.3 kJ
D)41 J
E)41 kJ

Question 59

A piece of copper with a mass of 218 g has a heat capacity of 83.9 J/°C.What is the specific heat of copper?

A)0.385 J/g·°C
B)1.83 × 10⁴ J/g·°C
C)2.60 J/g·°C
D)1.32 J/g·°C
E)24.5 J/g·°C

Question 60

How much heat is required to raise the temperature of 12.0 g of water from 15.4°C to 93.0°C? The specific heat of water is 4.184 J/g·°C.

A)223 J
B)773 J
C)503 J
D)4.67 ×10³ J
E)3.90 ×10³ J

Question 61

Pentaborane B₅H₉(s)burns vigorously in O₂ to give B₂O₃(s)and H₂O(l).What is ΔH° for the combustion of 1 mol of B₅H₉(s)? Substance ΔH°_f (kJ/mol)
B₂O₃(s) -1273.5
B₅H₉(s) +73.2
H₂O(l) -285.8

A)-1486.1 kJ
B)-1632.5 kJ
C)-4396.7 kJ
D)-4652.85 kJ
E)-9086.1 kJ

Question 62

When 0.560 g of Na(s)reacts with excess F₂(g)to form NaF(s),13.8 kJ of heat is evolved at standard-state conditions.What is the standard enthalpy of formation (ΔH°_f)of NaF(s)?

A)567 kJ/mol
B)-24.8 kJ/mol
C)-7.8 kJ/mol
D)24.8 kJ/mol
E)-567 kJ/mol

Question 63

What is ΔH°_rxn for the following reaction? 2C₈H₁₈(l)+ 17O₂(g)→ 16CO(g)+ 18H₂O(l)
2C₈H₁₈(l)+ 25O₂(g)→ 16CO₂(g)+ 18H₂O(l)
ΔH°_rxn = -11020.kJ/mol
2CO(g)+ O₂(g)→ 2CO₂(g)
ΔH°_rxn = -566.0 kJ/mol

A)-11020.kJ/mol
B)+6492 kJ/mol
C)-1964 kJ/mol
D)-6492 kJ/mol
E)-11586 kJ/mol

Question 64

What is the standard enthalpy change for the decomposition of one mole of SO₃? 2SO₂ + O₂→ 2SO₃ ΔH°_rxn = -198 kJ/mol

A)198 kJ/mol
B)-99.0 kJ/mol
C)99.0 kJ/mol
D)396 kJ/mol
E)-396 kJ/mol

Question 65

What is ΔH°_rxn for the following reaction? 2H₂O₂(l)→ 2H₂O(l)+ O₂(g)
ΔH°_f(H₂O(l))= -285.8 kJ/mol,ΔH°_f(H₂O₂(l))= -187.6 kJ/mol

A)-196.4 kJ/mol
B)98.2 kJ/mol
C)-98.2 kJ/mol
D)-473.4 kJ/mol
E)-946.8 kJ/mol

Question 66

Which represents an enthalpy change at 25 °C and 1 atm that is equal to ΔH^o_f for H₂O(l)?

A)O₂(g)+ 2H₂(g)→ 2H₂O(l)
B)½O₂(g)+ H (g)→ H₂O(g)
C)H₂(g)+ ½O₂(g)+ → H₂O(l)
D)2H₂O(l)→ O₂(g)+ 2H₂(g)
E)H₂O(l)→ ½O₂(g)+ H₂(g)

Question 67

Based on the following thermochemical equations,what is the heat of vaporization of titanium(IV)chloride? Ti(s)+ 2 Cl₂(g)→ TiCl₄(l)
ΔH = -804.2 kJ/mol
TiCl₄(g)→ 2 Cl₂(g)+ Ti(s)
ΔH = 763.2 kJ/mol

A)+41.0 kJ/mol
B)-1567.4 kJ/mol
C)1567 kJ/mol
D)-41.0 kJ/mol
E)-763.7 kJ/mol

Question 68

Glycine,C₂H₅O₂N,is important for biological energy.The combustion reaction of glycine is described by the following thermochemical equation. 4C₂H₅O₂N(s)+ 9O₂(g)→ 8CO₂(g)+ 10H₂O(l)+ 2N₂(g)ΔH°_rxn = -3896 kJ/mol
What is the standard enthalpy of formation of solid glycine?

A)-51.90 kJ/mol
B)-527.5 kJ/mol
C)-974.0 kJ/mol
D)-1502 kJ/mol
E)-2476 kJ/mol

Question 69

Octane (C₈H₁₈)undergoes combustion according to the following thermochemical equation. 2C₈H₁₈(l)+ 25O₂(g)→ 16CO₂(g)+ 18H₂O(l)ΔH°_rxn = -1.0940 × 10⁴kJ/mol
What is the standard enthalpy of formation of liquid octane?
ΔH°_f(CO₂(g))= -393.5 kJ/mol and ΔH°_f(H₂O(l))= -285.8 kJ/mol

A)-250 kJ/mol
B)-10,940.kJ/mol
C)-2188 kJ/mol
D)-495 kJ/mol
E)495 kJ/mol

Question 70

Which equation has a ΔH_rxn that is not equal to ΔH^o_f of the product?

A)O₂(g)+ H₂(g)→ H₂O₂(g)
B)½O₂(g)+ H₂(g)→ H₂O(g)
C)H₂(g)+ ½O₂(g)+ → H₂O(l)
D)NO(g)+ ½O₂(g)→ NO₂(l)
E)½H₂(g)+ ½Cl₂(g)→ HCl(g)

Question 71

Styrene,C₈H₈,is one of the substances used in the production of synthetic rubber.When styrene burns in oxygen to form carbon dioxide and liquid water under standard-state conditions at 25°C,42.15 kJ are released per gram of styrene.Find the standard enthalpy of formation of styrene at 25°C. ΔH°_f(CO₂(g))= -393.5 kJ/mol,ΔH°_f(H₂O(l))= -285.8 kJ/mol

A)-4390 kJ/mol
B)-1044 kJ/mol
C)-8681 kJ/mol
D)+99 kJ/mol
E)+637 kJ/mol

Question 72

Which equation has a ΔH_rxn that is not equal to ΔH^o_f of the product? rev: 04_28_2015_QC_CS-14747

A)F₂(g)+ ½O₂(g)→ F₂O(g)
B)O₂(g)+ 2H₂(g)→ 2 H₂O(g)
C)H₂(g)+ ½O₂(g)+ → H₂O(l)
D)Ti(s)+ 2Cl₂(g)→ TiCl₄(l)
E)½H₂(g)+ ½ Cl₂(g)→ HCl(g)

Question 73

Which of the following has a standard enthalpy of formation value (ΔH°_f)of zero at 298 K?

A)H₂O(g)
B)O(g)
C)H₂O(l)
D)O₂(g)
E)O₃(g)

Question 74

The heat of solution of ammonium nitrate is 26.2 kJ/mol.If a 5.368 g sample of NH₄NO₃ is added to 40.0 mL of water in a calorimeter at 23.5°C,what is the final temperature of the solution? The specific heat of water is 4.18 J/g·°C and the heat capacity of the calorimeter is 0.650 kJ/°C.

A)14.3°C
B)20.8°C
C)-7.7°C
D)25.6°C
E)21.4°C

Question 75

Given that CaO(s)+ H₂O(l)→ Ca(OH)₂(s),ΔH°_rxn = -64.8 kJ/mol,how many grams of CaO must react in order to liberate 525 kJ of heat?

A)6.92 g
B)56.1 g
C)454 g
D)606 g
E)3.40 × 10⁴ g

Question 76

What is ΔH°_rxn for the reaction 2Al₂O₃(s)→ 4Al(s)+ 3O₂(g)? ΔH°_f(Al₂O₃(s))= -1670 kJ/mol

A)3340 kJ/mol
B)1670 kJ/mol
C)-3340 kJ/mol
D)-1670 kJ/mol
E)-835 kJ/mol

Question 77

What is the standard enthalpy of formation of liquid methanol,CH₃OH(l)? C(graphite)+ O₂(g)→ CO₂(g)
ΔH°_rxn = -393.5 kJ/mol
H₂(g)+ ½O₂→ H₂O(l)
ΔH°_rxn = -285.8 kJ/mol
CH₃OH(l)+ 3/2O₂(g)→ CO₂(g)+ 2H₂O(l)
ΔH°_rxn = -726.4 kJ/mol

A)-1691.5 kJ/mol
B)-238.7 kJ/mol
C)1691.5 kJ/mol
D)47.1 kJ/mol
E)-47.1 kJ/mol

Question 78

Calculate the standard enthalpy change for the reaction 2C₈H₁₈(l)+ 21O₂(g)→ 8CO(g)+ 8CO₂(g)+ 18H₂O(l).Given:
2C₈H₁₈(l)+ 25O₂(g)→ 16CO₂(g)+ 18H₂O(l)
ΔH° = -11,020.kJ/mol
2CO(g)+ O₂(g)→ 2CO₂(g)
ΔH° = -566.0 kJ/mol

A)1.0454 × 10⁴ kJ/mol
B)-8756 kJ/mol
C)1.1586 × 10⁴ kJ/mol
D)-6492 kJ/mol
E)-1.0454 × 10⁴ kJ/mol

Question 79

The combustion of pentane produces heat according to the following thermochemical equation. C₅H₁₂(l)+ 8O₂(g)→ 5CO₂(g)+ 6H₂O(l)ΔH°_rxn = -3510 kJ/mol
How many grams of CO₂ is produced per 2.50 × 10³ kJ of heat released?

A)6.27 g
B)31.3 g
C)61.8 g
D)157 g
E)220 g

Question 80

What is ΔH°_rxn for the following reaction? C₆H₆(l)+ 15/2 O₂(g)→ 6CO₂(g)+ 3H₂O(l)
6C(graphite)+ 3H₂(g)→ C₆H₆(l)
ΔH°_rxn = +49.0 kJ/mol
C(graphite)+ O₂(g)→ CO₂(g)
ΔH°_rxn = -393.5 kJ/mol
H₂(g)+ ½O₂(g)→ H₂O(l)
ΔH°_rxn = -285.8 kJ/mol

A)-630.3 kJ/mol
B)-2597.8 kJ/mol
C)-3169.4kJ/mol
D)-3267.4 kJ/mol
E)630.3 kJ/mol