Deck 8: Thermodynamics: the First Law

Question 1

In a system composed of nitrogen gas in a cylinder fitted with a piston,when 2.00 kJ of energy is transferred as heat at an external pressure of 2.00 atm,the nitrogen gas expands from 2.00 to 5.00 L against this constant pressure.What is U for the process?

A)(0.608 kJ)
B)(+1.39 kJ)
C)(+2.61 kJ)
D)0
E)(2.61 kJ)

Answer 1

(+1.39 kJ)

Question 2

What is the total motional contribution to the molar internal energy of gaseous BF₃?

A)RT
B)3.5RT
C)3RT
D)1.5RT
E)2.5RT

Answer 2

3RT

Question 3

If 2.00 mol of an ideal gas at 300 K and 3.00 atm expands from 6.00 L to 18.00 L and has a final pressure of 1.20 atm,isothermally and reversibly,which of the following is correct?

A)w = 5.48 kJ, q = +5.48 kJ, U = 0
B)w = 3.65 kJ, q = +3.65 kJ, U = 0
C)w = +3.65 kJ, q = +3.65 kJ, U = +7.30 kJ
D)w = 5.48 kJ, q = 5.48 kJ, U = 11.0 kJ
E)w = +5.48 kJ, q = +5.48 kJ, U = +11.0 kJ

Answer 3

w = 5.48 kJ, q = +5.48 kJ, U = 0

Question 4

How much work is done by a person of mass 185 kg who climbs a ladder to the top of his house,a total of 15.0 m?

A)2.78 kJ
B)12.3 kJ
C)27.2 kJ
D)No work is done.
E)121 kJ

Question 5

What is the total motional contribution to the molar internal energy of gaseous H₂O at 25C?

A)6.19 kJmol^1
B)7.43 kJmol^1
C)3.72 kJmol^1
D)12.4 kJmol^1
E)2.48 kJmol^1

Question 6

Work is reported in joules; and 1 joule = ____________

Question 7

A CD player and its battery together do 500 kJ of work.The battery also releases 250 kJ of energy as heat,and the CD player releases 50 kJ as heat due to friction from spinning.What is the change in internal energy of the system,with the system regarded as the battery alone? Assume that the battery does 500 kJ of work on the CD player,which then does the same amount of work on the surroundings.

A)+200 kJ
B)(800 kJ)
C)(750 kJ)
D)(50 kJ)
E)(700 kJ)

Question 8

A CD player and its battery together do 500 kJ of work.The battery also releases 250 kJ of energy as heat and the CD player releases 50 kJ as heat due to friction from spinning.What is the change in internal energy of the system,with the system regarded as the CD player alone? Assume that the battery does 500 kJ of work on the CD player,which then does the same amount of work on the surroundings.

A)(-550 kJ)
B)(50 kJ)
C)(950 kJ)
D)(800 kJ)
E)(+450 kJ)

Question 9

Hot coffee in a vacuum flask (thermos)is an example of a(n)__________________ (open,closed,isolated)system.

Question 10

A closed system can exchange energy with the surroundings.True or false?

Question 11

A system had 150 kJ of work done on it and its internal energy increased by 60 kJ.How much energy did the system gain or lose as heat?

A)The system lost 90 kJ of energy as heat.
B)The system lost 210 kJ of energy as heat.
C)The system gained 60 kJ of energy as heat.
D)The system gained 90 kJ of energy as heat.
E)The system gained 210 kJ of energy as heat.

Question 12

If an isolated system contained +5 kJ of energy,after 100 years U =

A)The answer is impossible to determine
B)Slightly less than +5 kJ.
C)+5 kJ.
D)0 kJ.
E)(5 kJ.)

Question 13

A CD player and its battery together do 500 kJ of work.The battery also releases 250 kJ of energy as heat and the CD player releases 50 kJ as heat due to friction from spinning.What is the change in internal energy of the system,with the system regarded as the battery and CD player together?

A)+200 kJ
B)(700 kJ)
C)(800 kJ)
D)(200 kJ)
E)(750 kJ)

Question 14

A battery does 35 kJ of work driving an electric motor and 7 kJ of heat are released.What is the change in internal energy of the system?

A)(35 kJ)
B)+42 kJ
C)(42 kJ)
D)(28 kJ)
E)+28 kJ

Question 15

An isolated system can exchange energy and small particles with the surroundings.True or false?

Question 16

When a gas expands into a vacuum,w = 0.True or false?

Question 17

If 2.00 mol of an ideal gas at 300 K and 3.00 atm expands from 6.00 L to 18.00 L and a final pressure of 1.20 atm in two steps: (1)the gas is cooled at constant volume until its pressure has fallen to 1.20 atm,and (2)it is heated and allowed to expand against a constant pressure of 1.20 atm until its volume reaches 18.00 L,which of the following is correct?

A)w = 0 for step (1)and w = 1.46 kJ for step (2)
B)w = 4.57 kJ for the overall process
C)w = 6.03 kJ for the overall process
D)w = 4.57 kJ for step (1)and w = 1.46 kJ for step (2)
E)w = 0 for the overall process

Question 18

A piece of a newly synthesized material of mass 25.0 g at 80.0C is placed in a calorimeter containing 100.0 g of water at 20.0C.If the final temperature of the system is 24.0C,what is the specific heat capacity of this material?

A)0.30 Jg^1(C)^1
B)7.46 Jg^1(C)^1
C)1.19 Jg^1(C)^1
D)4.76 Jg^1(C)^1
E)0.84 Jg^1(C)^1

Question 19

A piece of a newly synthesized material of mass 12.0 g at 88.0C is placed in a calorimeter containing 100.0 g of water at 20.0C.If the final temperature of the system is 24.0C,what is the specific heat capacity of this material?

A)10.2 Jg^1(C)^1
B)1.58 Jg^1(C)^1
C)2.18 Jg^1(C)^1
D)9.50 Jg^1(C)^1
E)0.54 Jg^1(C)^1

Question 20

What is the total motional contribution to the molar internal energy of gaseous HCN?

A)3RT
B)3.5RT
C)2.5RT
D)RT
E)1.5RT

Question 21

Which of the following is not a state function?

A)H
B)T
C)U
D)S
E)None; they are all state functions.

Question 22

How much heat is required to vaporize 50.0 g of water if the initial temperature of the water is 25.0C and the water is heated to its boiling point,where it is converted to steam? The specific heat capacity of water is 4.18 J(C)^1g^1 and the standard enthalpy of vaporization of water at its boiling point is 40.7 kJmol^1.

A)169 kJ
B)64.2 kJ
C)40.7 kJ
D)193 kJ
E)23.5 kJ

Question 23

Calculate the enthalpy change that occurs when 1 lb (454 g)of mercury freezes at its freezing point (234.3 K).The standard enthalpy of fusion of mercury is 2.29 kJmol^1.

A)(2.29 kJ)
B)(1.04  10³ kJ)
C)+5.18 kJ
D)+2.29 kJ
E)(5.18 kJ)

Question 24

Calculate the final temperature when 2.50 kJ of energy is transferred as heat to 1.50 mol BF₃ at 298 K and 1 atm at constant pressure.

A)82C
B)80C
C)159C
D)75C
E)92C

Question 25

Calculate the change in internal energy when 2.50 kJ of energy is transferred as heat to 1.50 mol N₂ at 298 K and 1 atm at constant volume.

A)(2.50 kJ)
B)+2.50 kJ
C)+1.00 kJ
D)(1.50 kJ)
E)+1.50 kJ

Question 26

Calculate the enthalpy change that occurs when 1.00 kg of acetone condenses at its boiling point (329.4 K).The standard enthalpy of vaporization of acetone is 29.1 kJmol^1.

A)(502 kJ)
B)(29.1 kJ)
C)(2.91  10⁴ kJ)
D)+502 kJ
E)+29.1 kJ

Question 27

A reaction known to release 4.00 kJ of heat takes place in a calorimeter containing 0.200 L of solution and the temperature rose by 6.14C.When 200 mL of hydrochloric acid was added to a small piece of calcium carbonate in the same calorimeter,the temperature rose by 4.25C.What is the heat output for this reaction?

A)0.0257 kJ(C)^1
B)0.941 kJ(C)^1
C)0.651 kJ(C)^1
D)2.77 kJ(C)^1
E)2.12 kJ(C)^1

Question 28

Calculate the change in internal energy when 2.50 kJ of energy is transferred as heat to 1.50 mol BF₃ at 298 K and 1 atm at constant volume.

A)+1.00 kJ
B)+2.50 kJ
C)(1.50 kJ)
D)(2.50 kJ)
E)+1.50 kJ

Question 29

A reaction known to release 2.00 kJ of heat takes place in a calorimeter containing 0.200 L of solution and the temperature rose by 4.46C.When 100 mL of nitric acid and 100 mL of sodium hydroxide were mixed in the same calorimeter,the temperature rose 2.01C.What is the heat output for the neutralization reaction?

A)0.0186 kJ(C)^1
B)0.448 kJ(C)^1
C)0.816 kJ(C)^1
D)17.9 kJ(C)^1
E)0.901 kJ(C)^1

Question 30

Calculate the change in internal energy when 2.50 kJ of energy is transferred as heat to 1.50 mol N₂ at 298 K and 1 atm at constant pressure.

A)+2.14 kJ
B)(1.79 kJ)
C)+2.50 kJ
D)(2.50 kJ)
E)+1.79 kJ

Question 31

Calculate the change in internal energy when 2.50 kJ of energy is transferred as heat to 1.50 mol BF₃ at 298 K and 1 atm at constant pressure.

A)+1.56 kJ
B)+2.50 kJ
C)1.87 kJ
D)(2.50 kJ)
E)(1.87 kJ)

Question 32

When a solution of 1.691 g of silver nitrate is mixed with an excess of sodium chloride in a calorimeter of heat capacity 216 J(C)^1,the temperature rises 3.03C.What is the reaction enthalpy?

A)(65.7 kJmol^1 )
B)(0.654 kJmol^1 )
C)+111 kJmol^1
D)+65.7 kJmol^1
E)+0.654 kJmol^1

Question 33

Calculate the final temperature when 2.50 kJ of energy is transferred as heat to 1.50 mol BF₃ at 298 K and 1 atm at constant volume.

A)100C
B)80C
C)67C
D)125C
E)92C

Question 34

The combustion of one mole of octane,C₈H₁₈(l),in a bomb calorimeter released 5460 kJ of heat at 298 K.The products of the reaction are carbon dioxide and liquid water.What is the enthalpy change for this reaction?

A)+5471 kJmol^1 )
B)(5460 kJmol^1 )
C)(5471 kJmol^1 )
D)(5449 kJmol^1 )
E)(+5460 kJmol^1 )

Question 35

The combustion of 1 mole of ethanol,C₂H₅OH(l),in a bomb calorimeter released 1240 kJ of heat.The products of the reaction are carbon dioxide and liquid water.What is the enthalpy change for this reaction?

A)(1245 kJmol^1 )
B)(1235 kJmol^1 )
C)(+1235 kJmol^1 )
D)(+1240 kJmol^1 )
E)(1240 kJmol^1 )

Question 36

The combustion of 1 mole of octane,C₈H₁₈(l),to produce carbon dioxide and liquid water has H_r = 5471 kJmol^1 at 298 K.What is the change in internal energy for this reaction?

A)(5460 kJmol^1 )
B)(5482 kJmol^1 )
C)(5449 kJmol^1 )
D)(5471 kJmol^1 )
E)(5493 kJmol^1 )

Question 37

Calculate the final temperature when 2.50 kJ of energy is transferred as heat to 1.50 mol N₂ at 298 K and 1 atm at constant volume.

A)80C
B)145C
C)159C
D)120C
E)105C

Question 38

The combustion of 1 mole of ethanol,C₂H₅OH(l),to produce carbon dioxide and gaseous water has H_r = 1235 kJmol^1 at 298 K.What is the change in internal energy for this reaction?

A)(1237 kJmol^1 )
B)(1240 kJmol^1 )
C)(1230 kJmol^1 )
D)(1247 kJmol^1 )
E)(1223 kJmol^1 )

Question 39

Calculate the final temperature when 2.50 kJ of energy is transferred as heat to 1.50 mol N₂ at 298 K and 1 atm at constant pressure.

A)75C
B)159C
C)80C
D)82C
E)92C

Question 40

Calculate the standard enthalpy of vaporization of liquid bromine if the standard enthalpy of sublimation of solid bromine is +40.1 kJmol^1 and the standard enthalpy of fusion of solid bromine is +10.6 kJmol^1.

A)(50.7 kJmol^1 )
B)(29.5 )kJmol^1
C)(+50.7 kJmol^1 )
D)(+14.8 kJmol^1 )
E)(+29.5 kJmol^1 )

Question 41

Calculate the standard reaction enthalpy for the reaction. N₂H₄(l)+ H₂(g) 2NH₃(g)
Given:
N₂H₄(l)+ O₂(g) N₂(g)+ 2H₂O(g)
H° = 543 kJmol^1
2H₂(g)+ O₂(g) 2H₂O(g)
H° = 484 kJmol^1
N₂(g)+ 3H₂(g) 2NH₃(g)
H° = 92.2 kJmol^1

A)(935 kJmol^1 )
B)(1119 kJmol^1 )
C)(151 kJmol^1 )
D)(59 kJmol^1 )
E)(243 kJmol^1 )

Question 42

What mass of propane,C₃H₈(g),must be burned to supply 2580 kJ of heat? The standard enthalpy of combustion of propane at 298 K is 2220 kJmol^1.

A)25.6 g
B)51.2 g
C)102 g
D)75.9 g
E)37.9 g

Question 43

Match the values with the correct enthalpy change.
Enthalpy
Value
H_f(C(g))
1300 kJmol^1
H_f(C(s),(graphite))
+717 kJmol^1
H_c(C₂H₂(g))
+31 kJmol^1
H_f(Br₂(g))
0

Question 44

Calculate the lattice enthalpy of silver chloride from the following data. enthalpy of formation of Ag(g): +284 kJmol^1
First ionization energy of Ag(g): +731 kJmol^1
Enthalpy of formation of Cl(g): +122 kJmol^1
Electron affinity of Cl(g): +349 (H = 349)kJmol^1
Enthalpy of formation of AgCl(s): 127 kJmol^1

A)1613 kJmol^1
B)915 kJmol^1
C)1037 kJmol^1
D)1359 kJmol^1
E)661 kJmol^1

Question 45

If the standard enthalpy of combustion of ethanol,C₂H₅OH(l),at 298 K is 1368 kJmol^1,what is the standard enthalpy of formation of ethanol? The standard enthalpies of formation of carbon dioxide and liquid water are 393.51 and 285.83 kJmol^1,respectively.

A)+688.7 kJmol^1
B)(344.3 kJmol^1
C)+276.5 kJmol^1 )
D)(276.5 kJmol^1 )
E)(688.7 kJmol^1 )

Question 46

The standard enthalpy of formation of NaCl(s)is 411 kJ/mol.In a Born-Haber cycle for the formation of NaCl(s),which enthalpy change(s)is/are endothermic?

A)the lattice enthalpy of NaCl(s)
B)the electron affinity of chlorine
C)the reverse of the lattice enthalpy of NaCl(s)
D)All of the enthalpy changes are endothermic except for the standard enthalpy of formation of NaCl(s).

Question 47

Calculate the standard reaction enthalpy for the following reaction. CH₄(g)+ H₂O(g) CO(g)+ 3H₂(g)
Given:
2H₂(g)+ CO(g) CH₃OH(l)
H° = 128.3 kJmol^1
2CH₄(g)+ O₂(g) 2CH₃OH(l)
H° = 328.1 kJmol^1
2H₂(g)+ O₂(g) 2H₂O(g)
H° = 483.6 kJmol^1

A)+155.5 kJmol^1
B)+ 216 kJmol^1
C)+412.1 kJmol^1
D)+42.0 kJmol^1
E)+206.1 kJmol^1

Question 48

The lattice enthalpy of calcium bromide is the energy change for the reaction

A)CaBr₂(s) Ca(g)+ 2Br(g)
B)CaBr₂(s) Ca²⁺(g)+ 2Br^(g)
C)Ca(s)+ Br₂(l) CaBr₂(s)
D)CaBr₂(s) Ca(g)+ Br₂(g)
E)Ca(g)+ 2Br(g) CaBr₂(g)

Question 49

Calculate the standard enthalpy of combustion of butane,C₄H₁₀(g),at 298 K from standard enthalpy of formation data.

Question 50

What mass of ethanol,C₂H₅OH(l),must be burned to supply 500 kJ of heat? The standard enthalpy of combustion of ethanol at 298 K is 1368 kJmol^1.

A)126 g
B)2.74 g
C)16.8 g
D)10.9 g
E)29.7 g

Question 51

Calculate the standard enthalpy of combustion of ethanol at 298 K from standard enthalpy of formation data.

A)(957.0 kJmol^1 )
B)(1367 kJmol^1 )
C)(687.5 kJmol^1 )
D)(1922 kJmol^1 )
E)(401.7 kJmol^1 )

Question 52

Calculate the lattice enthalpy of potassium chloride given the following enthalpy data.
K(s) K(g)
+89 kJmol^1
K(g) K⁺(g)+ e^
+418 kJmol^1
½Cl₂(g) Cl(g)
+122 kJmol^1
Cl(g)e^  Cl^(g)
349 kJmol^1
K(s)+ ½Cl₂(g) KCl(s)
437 kJmol^1

Question 53

Given the standard reaction enthalpies below: N₂(g)+ O₂  2NO(g)
H° = +180.5 kJmol^1
2NO₂(g) N₂(g)+ 2O₂(g)
H° = 66.4 kJmol^1
Calculate the standard reaction enthalpy for the oxidation of nitric oxide to nitrogen dioxide,shown below:
2NO(g)+ O₂(g) 2NO₂(g)

A)(114.1 kJmol^1 )
B)(246.9 kJmol^1 )
C)(114.1 kJmol^1 )
D)(294.6 kJmol^1 )
E)(246.9 kJmol^1 )

Question 54

If the standard enthalpy of combustion of octane,C₈H₁₈(l),at 298 K is 5471 kJmol^1,calculate the standard enthalpy of formation of octane.The standard enthalpies of formation of carbon dioxide and liquid water are 393.51 and 285.83 kJmol^1,respectively.

Question 55

Calculate the lattice enthalpy of calcium oxide from the following data. enthalpy of formation of Ca(g): +178 kJmol^1
First ionization energy of Ca(g): +590 kJmol^1
Second ionization energy of Ca(g): +1150 kJmol^1
Enthalpy of formation of O(g): +249 kJmol^1
First electron affinity of O(g): +141 (H = 141)kJmol^1
Second electron affinity of O(g): 844 (H = +844)kJmol^1
Enthalpy of formation of CaO(s): 635 kJmol^1

A)1817 kJmol^1
B)1391 kJmol^1
C)2235 kJmol^1
D)3754 kJmol^1
E)3505 kJmol^1

Question 56

The standard enthalpy of formation of ammonium perchlorate at 298 K is 295.31 kJmol^1.Write the equation that corresponds to this value.

Question 57

The lattice enthalpy of calcium oxide is the energy change for the reaction

A)CaO(s) Ca(g)+ O(g)
B)CaO(s) Ca(g)+ ½O₂(g)
C)Ca(g)+ O(g) CaO(g)
D)CaO(s) Ca²⁺(g)+ O^2(g)
E)Ca(s)+ ½O₂(g) CaO(s)

Question 58

Calculate the lattice enthalpy of potassium fluoride from the following data. enthalpy of formation of K(g): +89 kJmol^1
First ionization energy of K(g): +418 kJmol^1
Enthalpy of formation of F(g): +79 kJmol^1
Electron affinity of F(g): +328 (H = 328)kJmol^1
Enthalpy of formation of KF(s): 567 kJmol^1

A)1481 kJmol^1
B)825 kJmol^1
C)904 kJmol^1
D)497 kJmol^1
E)347 kJmol^1

Question 59

What equation corresponds to the standard enthalpy of formation of gaseous hydrogen atoms,which,at 298 K is +217 kJmol^1?

Question 60

If the standard reaction enthalpy for the reaction NO₂(g) NO(g)+ O(g)
Is needed,calculate it from the standard enthalpy of formation of ozone,+142.7 kJmol^1,and from the reactions listed below:
O₂(g) 2O(g)
H° = +498.4 kJmol^1
NO(g)+ O₃(g) NO₂(g)+ O₂(g)
H° = 200 kJmol^1

A)+355 kJmol^1
B)+555 kJmol^1
C)+192 kJmol^1
D)+592 kJmol^1
E)+306 kJmol^1

Question 61

Use the following information to determine the standard enthalpy of formation of NH₃(g). N-H bond enthalpy = 390 kJmol^1
H_f(H(g))= 217.9 kJmol^1
H_f(N(g))= 472.6 kJmol^1

A)(44 kJmol^1 )
B)(691 kJmol^1 )
C)(516 kJmol^1 )
D)(83 kJmol^1 )
E)(1170 kJmol^1 )

Question 62

The formation of solid calcium chloride from a gas of its ions is an exothermic process.True or false?

Question 63

The standard enthalpy of formation of gaseous water is 241.82 kJmol^-1 at 298 K.Estimate this value at 370 K.The molar heat capacities of hydrogen,oxygen,and gaseous water are 28.82,29.36,and 33.58 JK^1mol^1.

A)(241.82 kJmol^1 )
B)(243.25 kJmol^1 )
C)(242.54 kJmol^1 )
D)(240.39 kJmol^1 )
E)(241.10 kJmol^1 )

Question 64

Calculate the standard enthalpy of formation of bicyco[1.1.0]butane (shown below) given the standard enthalpies of formation of C(g)and H(g),717 and 218 kJmol^-1,respectively,and the average C-H and C-C bond enthalpies,412 and 348 kJmol^-1,respectively.

A)+175 kJmol^1
B)(472 kJmol^1 )
C)+312 kJmol^1
D)(36 kJmol^1 )
E)(124 kJmol^1 )

Question 65

Calculate the average H-S bond enthalpy in H₂S(g)given the standard enthalpies of formation for H₂S(g),H(g),and S(g): 20.1,218,and 223 kJmol^1,respectively.

A)340 kJmol^1
B)231 kJmol^1
C)10.1 kJmol^1
D)679 kJmol^1
E)461 kJmol^1

Question 66

Give H_r values for each of the following reactions from the information below.
H_f(HCl(g))= 92.31 kJmol^1
H-Cl bond enthalpy = +431 kJmol^1
O-H bond enthalpy = +463 kJmol^1
H_f(H₂O(g))= 241.8 kJmol^1
(a)2H(g)+ O(g) H₂O(g)
(b)H₂(g)+ Cl₂(g) 2HCl(g)
(c)H(g)+ Cl(g) HCl(g)

Question 67

Calculate the standard enthalpy of formation of potassium chloride given the following enthalpy data.
K(s) K(g)
+89 kJmol^1
K(g) K⁺(g)+ e^
+418 kJmol^1
½Cl₂(g) Cl(g)
+122 kJmol^1
Cl(g)e^  Cl^(g)
349 kJmol^1
KCl(s) K⁺(g)+ Cl^(g)
+717 kJmol^1

Question 68

Determine H_f(HCl(g))from the following data. H-Cl bond enthalpy = +431 kJmol^1
H_f(H(g))= +217.9 kJmol^1
H_f(Cl(g))= +121.4 kJmol^1

A)+92 kJmol^1
B)(261 kJmol^1 )
C)(431 kJmol^1 )
D)+431 kJmol^1
E)(92 kJmol^1 )

Question 69

Calculate the H-Br bond enthalpy given the standard enthalpies of formation for HBr(g),H(g),and Br(g): 36.2,218,and 112 kJmol^1,respectively.

A)320 kJmol^1
B)366 kJmol^1
C)124 kJmol^1
D)284 kJmol^1
E)196 kJmol^1

Question 70

For any isothermal process,U > 0 for an ideal gas.True or false?

Question 71

The formation of solid calcium oxide from a gas of its ions is an exothermic process and is equal to the reverse of the lattice enthalpy.

Question 72

For the reaction CO₂(aq) CO₂(g),H_r = 19.4 kJmol^1 at 298.At constant temperature and pressure,which of the following statements is true?

A)w = 0
B)(U = 2.48 kJ
C)(H <  U)
D)(H = U)
E)(H > U)

Question 73

An isothermal change is one that occurs at a constant temperature.True or false?

Question 74

Combustion reactions can be exothermic or endothermic.True or false?

Question 75

The enthalpy of sublimation of a substance is related to its enthalpy of vaporization and enthalpy of fusion by the equation,H_sublimation = H_vaporization  H_fusion.True or false?

Question 76

At constant pressure and temperature,which of the following statements is true for the reaction: N₂O₅(s) 2NO₂(g)+ ½O₂(g),H_r = 109.5 kJmol^1 at 298 K.

A)(H is independent of the physical states of the reactants.)
B)(H = U)
C)w = 0
D)(H < U)
E)(H > U)

Question 77

Calculate the Br-Br bond enthalpy given the standard enthalpies of formation for Br₂(g)and Br(g),30.7 and 112 kJmol^1,respectively.

A)193 kJmol^1
B)255 kJmol^1
C)143 kJmol^1
D)81 kJmol^1
E)30.7 kJmol^1

Question 78

The standard enthalpy of formation of ammonia gas is 46.11 kJmol^1 at 298 K.What is the standard reaction enthalpy for the Haber process at 500C? The molar heat capacities of nitrogen,hydrogen,and ammonia are 29.12,28.82,and 35.06 JK^1mol^1 respectively.

A)(97.65 kJmol^1 )
B)(113.81 kJmol^1 )
C)(56.91 kJmol^1 )
D)(92.22 kJmol^1 )
E)(103.09 kJmol^1 )

Question 79

The heat flow for the reaction C₂H₆(g)+ 3.5O₂(g) 2CO₂(g)+ 3H₂O(l)
Measured in a bomb calorimeter is 1553.5 kJ/mol at 298 K.At this temperature,U is

A)(1553.5 kJ/mol)
B)(1552.3 kJ/mol)
C)(1547.3 kJ/mol)
D)(1559.7 kJ/mol)

Question 80

The molar heat capacity of a monatomic ideal gas is independent of temperature and pressure.True or false?