Question 1

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 2

Use Hess's Law to calculate the enthalpy change for the reaction WO3(s) + 3H2(g) → W(s) + 3H2O(g)
From the following data:
2W(s) + 3O2(g) → 2WO3(s) ΔH = −1685.4 kJ
2H2(g) + O2(g) → 2H2O(g) ΔH = −477.84 kJ

Accepted Answer

A) 125.9 kJ 
B) 252.9 kJ 
C) 364.9 kJ 
D) 1207.6 kJ 
E) None of these choices are correct. 
A) 125.9 kJ 
B) 252.9 kJ 
C) 364.9 kJ 
D) 1207.6 kJ 
E) None of these choices are correct.

Question 3

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

Accepted Answer

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

Question 4

Calculate the ΔH°rxn for the following reaction. (ΔH°f [SiO2(s)] = −910.9 kJ/mol; ΔH°f [SiCl4(g)] = −657.0 kJ/mol; ΔH°f [HCl(g)] = −92.3 kJ/mol; ΔH°f [H2O(g)] = −241.8 kJ/mol)
SiO2(s) + 4HCl(g) → SiCl4(g) + 2H2O(g)

Accepted Answer

A) −139.5 kJ 
B) −137.4 kJ 
C) −104.4 kJ 
D) 104.4 kJ 
E) 139.5 kJ 
A) −139.5 kJ 
B) −137.4 kJ 
C) −104.4 kJ 
D) 104.4 kJ 
E) 139.5 kJ

Question 5

The Starship Enterprise is caught in a time warp and Spock is forced to use the primitive techniques of the 20th century to determine the specific heat capacity of an unknown mineral. The 307-g sample 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/K. The final temperature in the calorimeter was 32.4°C. What is the specific heat capacity of the mineral?

Accepted Answer

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

Question 6

Cold packs, whose temperatures are lowered when ammonium nitrate dissolves in water, are carried by athletic trainers when transporting ice is not possible. Which of the following is true of this reaction?

Accepted Answer

A) Δ H  0, process is exothermic 
C) Δ H  0, process is endothermic 
E) Δ H = 0, since cold packs are sealed 
A) Δ H  0, process is exothermic 
C) Δ H  0, process is endothermic 
E) Δ H = 0, since cold packs are sealed

Question 7

Which one of the following statements about standard states is incorrect?

Accepted Answer

A) The standard state of a solid compound is the pure solid. 
B) The standard state of a liquid compound is the pure liquid. 
C) The standard state of a gaseous compound is the gas at a pressure of 1 atmosphere. 
D) The standard state of an aqueous solute is a saturated solution in water. 
E) The standard state of an element is the form in which it is stable at 1 atm and a specified temperature, usually 25°C. 
A) The standard state of a solid compound is the pure solid. 
B) The standard state of a liquid compound is the pure liquid. 
C) The standard state of a gaseous compound is the gas at a pressure of 1 atmosphere. 
D) The standard state of an aqueous solute is a saturated solution in water. 
E) The standard state of an element is the form in which it is stable at 1 atm and a specified temperature, usually 25°C.

Question 8

Calculate q when 28.6 g of water is heated from 22.0°C to 78.3°C.

Accepted Answer

A) 0.385 kJ 
B) 1.61 kJ 
C) 6.74 kJ 
D) 9.37 kJ 
E) 1.61 × 10 3 kJ 
A) 0.385 kJ 
B) 1.61 kJ 
C) 6.74 kJ 
D) 9.37 kJ 
E) 1.61 × 10 3 kJ

Question 9

In which one of the following reactions would you expect ΔH to be substantially greater than ΔE (i.e., ΔH > ΔE)?

Accepted Answer

A) H 2( g)+ Br 2( g)→ 2HBr( g) 
B) CO 2( s)→ CO 2( g) 
C) C 2H 2( g)+ H 2( g)→ C 2H 4( g) 
D) H 2O( s)→ H 2O( l) 
E) HCl( aq)+ NaOH( aq)→ NaCl( aq)+ H 2O( l) 
A) H 2( g)+ Br 2( g)→ 2HBr( g) 
B) CO 2( s)→ CO 2( g) 
C) C 2H 2( g)+ H 2( g)→ C 2H 4( g) 
D) H 2O( s)→ H 2O( l) 
E) HCl( aq)+ NaOH( aq)→ NaCl( aq)+ H 2O( l)

Question 10

A system delivers 225 J of heat to the surroundings while delivering 645 J of work. Calculate the change in the internal energy, ΔE, of the system.

Accepted Answer

A) −420 J 
B) 420 J 
C) −870 J 
D) 870 J 
E) −225 J 
A) −420 J 
B) 420 J 
C) −870 J 
D) 870 J 
E) −225 J

Question 11

The dissolution of barium hydroxide in water is an exothermic process. Which of the following statements is correct?

Accepted Answer

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. 
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 12

For which one of the following reactions will ΔH be approximately (or exactly) equal to ΔE?

Accepted Answer

A) H 2( g)+ Br 2( g)→ 2HBr( g) 
B) H 2O( l)→ H 2O( g) 
C) CaCO 3( s)→ CaO( s)+ CO 2( g) 
D) 2H( g)+ O( g)→ H 2O( l) 
E) CH 4( g)+ 2O 2( g)→ CO 2( g)+ 2H 2O( l) 
A) H 2( g)+ Br 2( g)→ 2HBr( g) 
B) H 2O( l)→ H 2O( g) 
C) CaCO 3( s)→ CaO( s)+ CO 2( g) 
D) 2H( g)+ O( g)→ H 2O( l) 
E) CH 4( g)+ 2O 2( g)→ CO 2( g)+ 2H 2O( l)

Question 13

Stoichiometric amounts of nitrogen gas and hydrogen gas react in a calorimeter to produce 5.00 g of ammonia gas. The calorimeter temperature rises 0.42°C. The calorimeter and water have a combined heat capacity of 32.16 kJ/K. Calculate the heat of formation of ammonia, ΔHf°, in kJ/mol. The formation reaction for ammonia is: 0.5N2(g) + 1.5H2(g) → NH3(g).

Accepted Answer

A) −46 kJ/mol 
B) −13.5 kJ/mol 
C) −3.97 kJ/mol 
D) 3.97 kJ/mol 
E) 13.5 kJ/mol 
A) −46 kJ/mol 
B) −13.5 kJ/mol 
C) −3.97 kJ/mol 
D) 3.97 kJ/mol 
E) 13.5 kJ/mol

Question 14

In a phase change of water between the liquid and the gas phases, 770.1 kJ of energy was released by the system. What was the product, and how much of it was formed in the phase change? (Data: H2O(l) → H2O(g) ΔH = 44.01 kJ/mol.)

Accepted Answer

A) 315 g water vapor was produced. 
B) 17.5 g of water vapor was produced. 
C) 17.5 mol of water vapor was produced. 
D) 17.5 mol of liquid water was produced. 
E) 17.5 g of liquid water was produced. 
A) 315 g water vapor was produced. 
B) 17.5 g of water vapor was produced. 
C) 17.5 mol of water vapor was produced. 
D) 17.5 mol of liquid water was produced. 
E) 17.5 g of liquid water was produced.

Question 15

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

Accepted Answer

A) 32.7 kJ 
B) 46.5 kJ 
C) 75.9 kJ 
D) 82.8 kJ 
E) 89.7 kJ 
A) 32.7 kJ 
B) 46.5 kJ 
C) 75.9 kJ 
D) 82.8 kJ 
E) 89.7 kJ

Question 16

The only way in which a system can do work on the surroundings is by expansion against the external pressure.

Accepted Answer

A) True 
 B)False

Question 17

Ethanol, C2H5OH, is being promoted as a clean fuel and is used as an additive in many gasoline mixtures. Calculate the ΔH°rxnfor the combustion of ethanol. (ΔH°f [C2H5OH(l)] = −277.7 kJ/mol; ΔH°f [CO2(g)] = −393.5 kJ/mol; ΔH°f [H2O(g)] = −241.8 kJ/mol)

Accepted Answer

A) −1234.7 kJ 
B) −751.1 kJ 
C) −357.6 kJ 
D) 357.6 kJ 
E) 1234.7 kJ 
A) −1234.7 kJ 
B) −751.1 kJ 
C) −357.6 kJ 
D) 357.6 kJ 
E) 1234.7 kJ

Question 18

Calculate the ΔH°rxn for the decomposition of calcium carbonate to calcium oxide and carbon dioxide. ΔH°f [CaCO3(s)] = −1206.9 kJ/mol; ΔH°f [CaO(s)] = −635.1 kJ/mol;
ΔH°f [CO2(g)] = −393.5 kJ/mol
CaCO3(s) → CaO(s) + CO2(g)

Accepted Answer

A) −2235.5 kJ 
B) −1448.5 kJ 
C) −178.3 kJ 
D) 178.3 kJ 
E) 2235.5 kJ 
A) −2235.5 kJ 
B) −1448.5 kJ 
C) −178.3 kJ 
D) 178.3 kJ 
E) 2235.5 kJ

Question 19

Which one of the following equations represents the formation reaction of CH3OH(l)?

Accepted Answer

A) C( g)+ 2H 2( g)+ ½O 2( g)→ CH 3OH( l) 
B) C( g)+ 4H( g)+ O( g)→ CH 3OH( l) 
C) C(graphite)+ 4H( g)+ O( g)→ CH 3OH( l) 
D) C(diamond)+ 4H( g)+ O( g)→ CH 3OH( l) 
E) C(graphite)+ 2H 2( g)+ ½O 2( g)→ CH 3OH( l) 
A) C( g)+ 2H 2( g)+ ½O 2( g)→ CH 3OH( l) 
B) C( g)+ 4H( g)+ O( g)→ CH 3OH( l) 
C) C(graphite)+ 4H( g)+ O( g)→ CH 3OH( l) 
D) C(diamond)+ 4H( g)+ O( g)→ CH 3OH( l) 
E) C(graphite)+ 2H 2( g)+ ½O 2( g)→ CH 3OH( l)

Question 20

A system receives 575 J of heat and delivers 425 J of work. Calculate the change in the internal energy, ΔE, of the system.

Accepted Answer

A) −150 J 
B) 150 J 
C) −l000 J 
D) 1000 J 
E) 575 J 
A) −150 J 
B) 150 J 
C) −l000 J 
D) 1000 J 
E) 575 J

Exam 6: Thermochemistry: Energy Flow and Chemical Change

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

Use Hess's Law to calculate the enthalpy change for the reaction WO3(s) + 3H2(g) → W(s) + 3H2O(g) From the following data: 2W(s) + 3O2(g) → 2WO3(s) ΔH = −1685.4 kJ 2H2(g) + O2(g) → 2H2O(g) ΔH = −477.84 kJ

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

Calculate the ΔH°rxn for the following reaction. (ΔH°f [SiO2(s)] = −910.9 kJ/mol; ΔH°f [SiCl4(g)] = −657.0 kJ/mol; ΔH°f [HCl(g)] = −92.3 kJ/mol; ΔH°f [H2O(g)] = −241.8 kJ/mol) SiO2(s) + 4HCl(g) → SiCl4(g) + 2H2O(g)

Cold packs, whose temperatures are lowered when ammonium nitrate dissolves in water, are carried by athletic trainers when transporting ice is not possible. Which of the following is true of this reaction?

Which one of the following statements about standard states is incorrect?

Calculate q when 28.6 g of water is heated from 22.0°C to 78.3°C.

In which one of the following reactions would you expect ΔH to be substantially greater than ΔE (i.e., ΔH > ΔE)?

A system delivers 225 J of heat to the surroundings while delivering 645 J of work. Calculate the change in the internal energy, ΔE, of the system.

The dissolution of barium hydroxide in water is an exothermic process. Which of the following statements is correct?

For which one of the following reactions will ΔH be approximately (or exactly) equal to ΔE?

In a phase change of water between the liquid and the gas phases, 770.1 kJ of energy was released by the system. What was the product, and how much of it was formed in the phase change? (Data: H2O(l) → H2O(g) ΔH = 44.01 kJ/mol.)

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

The only way in which a system can do work on the surroundings is by expansion against the external pressure.

Ethanol, C2H5OH, is being promoted as a clean fuel and is used as an additive in many gasoline mixtures. Calculate the ΔH°rxnfor the combustion of ethanol. (ΔH°f [C2H5OH(l)] = −277.7 kJ/mol; ΔH°f [CO2(g)] = −393.5 kJ/mol; ΔH°f [H2O(g)] = −241.8 kJ/mol)

Calculate the ΔH°rxn for the decomposition of calcium carbonate to calcium oxide and carbon dioxide. ΔH°f [CaCO3(s)] = −1206.9 kJ/mol; ΔH°f [CaO(s)] = −635.1 kJ/mol; ΔH°f [CO2(g)] = −393.5 kJ/mol CaCO3(s) → CaO(s) + CO2(g)

Which one of the following equations represents the formation reaction of CH3OH(l)?

A system receives 575 J of heat and delivers 425 J of work. Calculate the change in the internal energy, ΔE, of the system.

Keys to the Study of Chemistry: Definitions, Units, and Problem Solving

The Components of Matter

Stoichiometry of Formulas and Equations

Three Major Classes of Chemical Reactions

Gases and the Kinetic-Molecular Theory

Quantum Theory and Atomic Structure

Electron Configuration and Chemical Periodicity

Models of Chemical Bonding

The Shapes of Molecules

Theories of Covalent Bonding

Intermolecular Forces: Liquids, Solids, and Phase Changes

The Properties of Mixtures: Solutions and Colloids

Periodic Patterns in the Main-Group Elements

Organic Compounds and the Atomic Properties of Carbon

Kinetics: Rates and Mechanisms of Chemical Reactions

Equilibrium: the Extent of Chemical Reactions

Acid-Base Equilibria

Ionic Equilibria in Aqueous Systems

Thermodynamics: Entropy, Free Energy, and Reaction Direction

Electrochemistry: Chemical Change and Electrical Work

The Elements in Nature and Industry

Transition Elements and Their Coordination Compounds

Nuclear Reactions and Their Applications

Filters

Use Hess's Law to calculate the enthalpy change for the reaction WO₃(s) + 3H₂(g) → W(s) + 3H₂O(g) From the following data: 2W(s) + 3O₂(g) → 2WO₃(s) ΔH = −1685.4 kJ 2H₂(g) + O₂(g) → 2H₂O(g) ΔH = −477.84 kJ

Calculate the ΔH°_rxnfor the following reaction. (ΔH°_f [SiO₂(s)] = −910.9 kJ/mol; ΔH°_f [SiCl₄(g)] = −657.0 kJ/mol; ΔH°_f [HCl(g)] = −92.3 kJ/mol; ΔH°_f [H₂O(g)] = −241.8 kJ/mol) SiO₂(s) + 4HCl(g) → SiCl₄(g) + 2H₂O(g)

In a phase change of water between the liquid and the gas phases, 770.1 kJ of energy was released by the system. What was the product, and how much of it was formed in the phase change? (Data: H₂O(l) → H₂O(g) ΔH = 44.01 kJ/mol.)

Ethanol, C₂H₅OH, is being promoted as a clean fuel and is used as an additive in many gasoline mixtures. Calculate the ΔH°_rxnfor the combustion of ethanol. (ΔH°_f [C₂H₅OH(l)] = −277.7 kJ/mol; ΔH°_f [CO₂(g)] = −393.5 kJ/mol; ΔH°_f [H₂O(g)] = −241.8 kJ/mol)

Calculate the ΔH°_rxn for the decomposition of calcium carbonate to calcium oxide and carbon dioxide. ΔH°_f [CaCO₃(s)] = −1206.9 kJ/mol; ΔH°_f [CaO(s)] = −635.1 kJ/mol; ΔH°_f [CO₂(g)] = −393.5 kJ/mol CaCO₃(s) → CaO(s) + CO₂(g)

Which one of the following equations represents the formation reaction of CH₃OH(l)?