Question 1

Using Hess' law, what is ΔH°rxn at 25°C for the following reaction? ClF(g) + F2(g) → ClF3(g)

Accepted Answer

A)  -217.5 kJ/mol 
B)  -130.2 kJ/mol 
C)  217.5 kJ/mol 
D)  -108.7 kJ/mol 
E)  465.4 kJ/mol 
A)  -217.5 kJ/mol 
B)  -130.2 kJ/mol 
C)  217.5 kJ/mol 
D)  -108.7 kJ/mol 
E)  465.4 kJ/mol

Question 2

The heat absorbed by a system at constant pressure is equal to ΔU + PΔV.

Accepted Answer

A) True 
 B)False

Question 3

Which equation has a ΔHrxn that is not equal to ΔHof of the product?

Accepted Answer

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) 
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 4

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.

Accepted Answer

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

Question 5

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

Accepted Answer

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) 
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 6

In an endothermic reaction, in going from the reactants to the products at the same temperature, the value of q is negative.

Accepted Answer

A) True 
 B)False

Question 7

How much heat is evolved if 0.600 kg of SO2 is burned in excess oxygen? 2SO2(g) + O2(g) → 2SO3(g) ΔH°rxn= -198 kJ/mol

Accepted Answer

A)  5.46 × 10-2 kJ 
B)  927 kJ 
C)  1.85 × 103 kJ 
D)  59,400 kJ 
E)  3.71 × 103 kJ 
A)  5.46 × 10-2 kJ 
B)  927 kJ 
C)  1.85 × 103 kJ 
D)  59,400 kJ 
E)  3.71 × 103 kJ

Question 8

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

Accepted Answer

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

Question 9

Given the following ΔH° values
H2(g) + ½O2(g) → H2O(l) ΔH°f = -285.8 kJ
H2O2(l) → H2(g) + O2(g) ΔH°rxn = 187.6 kJ
calculate ΔH°rxn for the reaction H2O2(l) → H2O(l) + ½O2(g),

Accepted Answer

Question 10

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

Accepted Answer

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

Question 11

Solid sodium peroxide (Na2O2) reacts with liquid water yielding aqueous sodium hydroxide and oxygen gas. How much heat is released if 327.2 g of oxygen gas is produced from the reaction of sodium peroxide and water under standard-state conditions?

Accepted Answer

A)  46,630 kJ 
B)  1457 kJ 
C)  6689 kJ 
D)  3345 kJ 
E)  2914 kJ 
A)  46,630 kJ 
B)  1457 kJ 
C)  6689 kJ 
D)  3345 kJ 
E)  2914 kJ

Question 12

Using Hess's law, what is ΔH°rxn for the following reaction? WO3(s) + 3H2(g) → W(s) + 3H2O(g)

Accepted Answer

A)  117.5 kJ/mol 
B)  235.0 kJ/mol 
C)  359.3 kJ/mol 
D)  1202.2 kJ/mol 
E)  2169.4 kJ/mol 
A)  117.5 kJ/mol 
B)  235.0 kJ/mol 
C)  359.3 kJ/mol 
D)  1202.2 kJ/mol 
E)  2169.4 kJ/mol

Question 13

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

Accepted Answer

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

Question 14

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?

Accepted Answer

A)  ΔU  0 
E)  q > 0 
A)  ΔU  0 
E)  q > 0

Question 15

What is ΔH°rxn for the following reaction? H3AsO4(aq) + 4H2(g) → AsH3(g) + 4H2O(l)

Accepted Answer

A)  -1876.3 kJ/mol 
B)  -1018.9 kJ/mol 
C)  -790.3 kJ/mol 
D)  -410.1 kJ/mol 
E)  -67.1 kJ/mol 
A)  -1876.3 kJ/mol 
B)  -1018.9 kJ/mol 
C)  -790.3 kJ/mol 
D)  -410.1 kJ/mol 
E)  -67.1 kJ/mol

Question 16

What is ΔH°rxn for the following reaction? SiO2(s) + 4HCl(g) → SiCl4(g) + 2H2O(g)

Accepted Answer

A)  -1856.2 kJ/mol 
B)  -1372.6 kJ/mol 
C)  -47.0 kJ/mol 
D)  82.1 kJ/mol 
E)  530.6 kJ/mol 
A)  -1856.2 kJ/mol 
B)  -1372.6 kJ/mol 
C)  -47.0 kJ/mol 
D)  82.1 kJ/mol 
E)  530.6 kJ/mol

Question 17

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

Accepted Answer

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. 
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.

Question 18

A 100.-g sample of Cu is heated to 400.oC and then plunged into 1000. g of water at 22.6oC. What is the final temperature? Specific heat capacity: Cu: 0.385 J/g·°C;water: 4.184 J/g·°C

Accepted Answer

Question 19

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

Accepted Answer

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) 
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 20

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?

Accepted Answer

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

Exam 5: Thermochemistry

Using Hess' law, what is ΔH°rxn at 25°C for the following reaction? ClF(g) + F2(g) → ClF3(g)

The heat absorbed by a system at constant pressure is equal to ΔU + PΔV.

Which equation has a ΔHrxn that is not equal to ΔHof of the product?

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.

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

In an endothermic reaction, in going from the reactants to the products at the same temperature, the value of q is negative.

How much heat is evolved if 0.600 kg of SO2 is burned in excess oxygen? 2SO2(g) + O2(g) → 2SO3(g) ΔH°rxn= -198 kJ/mol

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

Given the following ΔH° values H2(g) + ½O2(g) → H2O(l) ΔH°f = -285.8 kJ H2O2(l) → H2(g) + O2(g) ΔH°rxn = 187.6 kJ calculate ΔH°rxn for the reaction H2O2(l) → H2O(l) + ½O2(g),

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

Solid sodium peroxide (Na2O2) reacts with liquid water yielding aqueous sodium hydroxide and oxygen gas. How much heat is released if 327.2 g of oxygen gas is produced from the reaction of sodium peroxide and water under standard-state conditions?

Using Hess's law, what is ΔH°rxn for the following reaction? WO3(s) + 3H2(g) → W(s) + 3H2O(g)

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

What is ΔH°rxn for the following reaction? H3AsO4(aq) + 4H2(g) → AsH3(g) + 4H2O(l)

What is ΔH°rxn for the following reaction? SiO2(s) + 4HCl(g) → SiCl4(g) + 2H2O(g)

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

A 100.-g sample of Cu is heated to 400.oC and then plunged into 1000. g of water at 22.6oC. What is the final temperature? Specific heat capacity: Cu: 0.385 J/g·°C;water: 4.184 J/g·°C

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

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?

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Filters

Using Hess' law, what is ΔH°_rxnat 25°C for the following reaction? ClF(g) + F₂(g) → ClF₃(g)

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

How much heat is evolved if 0.600 kg of SO₂ is burned in excess oxygen? 2SO₂(g) + O₂(g) → 2SO₃(g) ΔH°_rxn= -198 kJ/mol

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

Given the following ΔH° values H₂(g) + ½O₂(g) → H₂O(l) ΔH°_f = -285.8 kJ H₂O₂(l) → H₂(g) + O₂(g) ΔH°_rxn = 187.6 kJ calculate ΔH°_rxn for the reaction H₂O₂(l) → H₂O(l) + ½O₂(g),

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

Solid sodium peroxide (Na₂O₂) reacts with liquid water yielding aqueous sodium hydroxide and oxygen gas. How much heat is released if 327.2 g of oxygen gas is produced from the reaction of sodium peroxide and water under standard-state conditions?

Using Hess's law, what is ΔH°_rxn for the following reaction? WO₃(s) + 3H₂(g) → W(s) + 3H₂O(g)

What is ΔH°_rxn for the following reaction? H₃AsO₄(aq) + 4H₂(g) → AsH₃(g) + 4H₂O(l)

What is ΔH°_rxn for the following reaction? SiO₂(s) + 4HCl(g) → SiCl₄(g) + 2H₂O(g)

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

A 100.-g sample of Cu is heated to 400.^oC and then plunged into 1000. g of water at 22.6^oC. What is the final temperature? Specific heat capacity: Cu: 0.385 J/g·°C;water: 4.184 J/g·°C

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