Question 1

What is ΔH°rxn for the decomposition of calcium carbonate to calcium oxide and carbon dioxide? CaCO3(s) → CaO(s) + CO2(g)

Accepted Answer

A)  -2236.0 kJ/mol 
B)  -1449.0 kJ/mol 
C)  -177.8 kJ/mol 
D)  177.8 kJ/mol 
E)  2236.0 kJ/mol 
A)  -2236.0 kJ/mol 
B)  -1449.0 kJ/mol 
C)  -177.8 kJ/mol 
D)  177.8 kJ/mol 
E)  2236.0 kJ/mol

Question 2

Which of the following processes always results in an increase in the energy of a system?

Accepted Answer

A)  The system loses heat and does work on the surroundings. 
B)  The system gains heat and does work on the surroundings. 
C)  The system loses heat and has work done on it by the surroundings. 
D)  The system gains heat and has work done on it by the surroundings. 
E)  None of these is always true. 
A)  The system loses heat and does work on the surroundings. 
B)  The system gains heat and does work on the surroundings. 
C)  The system loses heat and has work done on it by the surroundings. 
D)  The system gains heat and has work done on it by the surroundings. 
E)  None of these is always true.

Question 3

Ethanol, C2H5OH, is promoted as a clean fuel and is used as an additive in many gasoline mixtures. Calculate the ΔH°rxn for the combustion of ethanol.

Accepted Answer

A)  -1235.4 kJ 
B)  -751.8 kJ 
C)  -358.3 kJ 
D)  358.3 kJ 
E)  1235.4 kJ 
A)  -1235.4 kJ 
B)  -751.8 kJ 
C)  -358.3 kJ 
D)  358.3 kJ 
E)  1235.4 kJ

Question 4

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

Accepted Answer

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

Question 5

Consider the following two representations of chemical reactions. Each sphere represents 1 mol of atoms.   What is ΔHºrxn for the following reaction? CS(g) + O(g) → CO(g) + S(g)

Accepted Answer

A)  -359 kJ/mol 
B)  1434 kJ/mol 
C)  -7142 kJ/mol 
D)  -1434 kJ/mol 
E)  7142 kJ/mol 
A)  -359 kJ/mol 
B)  1434 kJ/mol 
C)  -7142 kJ/mol 
D)  -1434 kJ/mol 
E)  7142 kJ/mol

Question 6

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

Accepted Answer

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

Question 7

Which represents the formation reaction for XeF4(g)? Each sphere represents 1 mol of atoms.

Accepted Answer

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

Question 8

Octane (C8H18) undergoes combustion according to the following thermochemical equation. 2C8H18(l) + 25O2(g) → 16CO2(g) + 18H2O(l) ΔH°rxn = -1.0940 × 104 kJ/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

Accepted Answer

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

Question 9

Chemical reactions in a bomb calorimeter occur at constant pressure.

Accepted Answer

A) True 
 B)False

Question 10

In which process is ΔH = ΔU?

Accepted Answer

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. 
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 11

________ is the amount of heat required to raise the temperature of one gram of a substance by one degree Celsius.

Accepted Answer

The answer of ________ is the amount of heat required...

Question 12

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

Accepted Answer

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) 
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 13

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

Accepted Answer

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

Question 14

Sand is converted to pure silicon in a three-step process. The final step in this process is as follows. SiCl4(g) + 2Mg(s) → 2MgCl(s) + Si(s) ΔH°rxn = -625.6 kJ/mol
What is the enthalpy change if 25.0 mol of silicon tetrachloride is converted to elemental silicon?

Accepted Answer

A)  -25.0 kJ 
B)  -626 kJ 
C)  -1.56 × l04 kJ 
D)  -3.13 × 104 kJ 
E)  -3.13 × 103 kJ 
A)  -25.0 kJ 
B)  -626 kJ 
C)  -1.56 × l04 kJ 
D)  -3.13 × 104 kJ 
E)  -3.13 × 103 kJ

Question 15

Which relationship is always correct?

Accepted Answer

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

Question 16

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)?

Accepted Answer

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

Question 17

To which one of the following reactions, occurring at 25oC, does the symbol ΔHof [H2SO4(l)] refer?

Accepted Answer

A)  H2(g) + S(s) + 2 O2(g)  H2SO4(l) 
B)  H2SO4(l)  H2(g) + S(s) + 2 O2(g) 
C)  H2(g) + S(g) + 2 O2(g)  H2SO4(l) 
D)  H2SO4(l)  2 H(g) + S(s) + 4 O(g) 
E)  2 H(g) + S(g) + 4 O(g)  H2SO4(l) 
A)  H2(g) + S(s) + 2 O2(g)  H2SO4(l) 
B)  H2SO4(l)  H2(g) + S(s) + 2 O2(g) 
C)  H2(g) + S(g) + 2 O2(g)  H2SO4(l) 
D)  H2SO4(l)  2 H(g) + S(s) + 4 O(g) 
E)  2 H(g) + S(g) + 4 O(g)  H2SO4(l)

Question 18

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

Accepted Answer

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 
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 19

How much heat is released if 35.0 g of ethanol (C2H5OH) burns in excess oxygen? C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l) ΔH°rxn = -1367 kJ/mol

Accepted Answer

A)  1797 kJ 
B)  1367 kJ 
C)  9.61 × 10-4 kJ 
D)  4.78 × 104 kJ 
E)  1040 kJ 
A)  1797 kJ 
B)  1367 kJ 
C)  9.61 × 10-4 kJ 
D)  4.78 × 104 kJ 
E)  1040 kJ

Question 20

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

Accepted Answer

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 
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

Exam 5: Thermochemistry

What is ΔH°rxn for the decomposition of calcium carbonate to calcium oxide and carbon dioxide? CaCO3(s) → CaO(s) + CO2(g)

Which of the following processes always results in an increase in the energy of a system?

Ethanol, C2H5OH, is promoted as a clean fuel and is used as an additive in many gasoline mixtures. Calculate the ΔH°rxn for the combustion of ethanol.

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

Consider the following two representations of chemical reactions. Each sphere represents 1 mol of atoms. What is ΔHºrxn for the following reaction? CS(g) + O(g) → CO(g) + S(g)

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

Which represents the formation reaction for XeF4(g)? Each sphere represents 1 mol of atoms.

Octane (C8H18) undergoes combustion according to the following thermochemical equation. 2C8H18(l) + 25O2(g) → 16CO2(g) + 18H2O(l) ΔH°rxn = -1.0940 × 104 kJ/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

Chemical reactions in a bomb calorimeter occur at constant pressure.

In which process is ΔH = ΔU?

________ is the amount of heat required to raise the temperature of one gram of a substance by one degree Celsius.

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

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

Sand is converted to pure silicon in a three-step process. The final step in this process is as follows. SiCl4(g) + 2Mg(s) → 2MgCl(s) + Si(s) ΔH°rxn = -625.6 kJ/mol What is the enthalpy change if 25.0 mol of silicon tetrachloride is converted to elemental silicon?

Which relationship is always correct?

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)?

To which one of the following reactions, occurring at 25oC, does the symbol ΔHof [H2SO4(l)] refer?

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

How much heat is released if 35.0 g of ethanol (C2H5OH) burns in excess oxygen? C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l) ΔH°rxn = -1367 kJ/mol

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

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What is ΔH°_rxn for the decomposition of calcium carbonate to calcium oxide and carbon dioxide? CaCO₃(s) → CaO(s) + CO₂(g)

Ethanol, C₂H₅OH, is promoted as a clean fuel and is used as an additive in many gasoline mixtures. Calculate the ΔH°_rxn for the combustion of ethanol.

Consider the following two representations of chemical reactions. Each sphere represents 1 mol of atoms. What is ΔHº_rxn for the following reaction? CS(g) + O(g) → CO(g) + S(g)

Which represents the formation reaction for XeF₄(g)? Each sphere represents 1 mol of atoms.

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

Sand is converted to pure silicon in a three-step process. The final step in this process is as follows. SiCl₄(g) + 2Mg(s) → 2MgCl(s) + Si(s) ΔH°_rxn = -625.6 kJ/mol What is the enthalpy change if 25.0 mol of silicon tetrachloride is converted to elemental silicon?

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)?

To which one of the following reactions, occurring at 25^oC, does the symbol ΔH^o_f [H₂SO₄(l)] refer?

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

How much heat is released if 35.0 g of ethanol (C₂H₅OH) burns in excess oxygen? C₂H₅OH(l) + 3O₂(g) → 2CO₂(g) + 3H₂O(l) ΔH°_rxn = -1367 kJ/mol

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