Question 1

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 0.800 atm. The value of w, in J, is

Accepted Answer

A)   -4.0 J.
B)   4.0 J.
C)   -405 J.
D)   405 J.
E)   4.05 × 103 J. D

Question 2

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

Accepted Answer

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

Question 3

Consider the equation F1F1F1S1F1F1F10E = q + w
Explain fully the meaning of all three terms in the equation, and also the implied sign convention for q and w.

Accepted Answer

E is the internal energy of a system, i.e., the total energy of all forms of energy in the system. So, F1F1F1S1F1F1F10E is the change internal energy of the system; q is heat transferred to or from the system, w is work done on or by the system. The sign convention is that q and w are positive when the system gains energy; i.e., heat transferred to the system, or work done on the system, are both positive.

Question 4

a. Explain fully what is meant by the term "state function."
b. (i) Give two examples of thermodynamic quantities which state functions.
(ii) Give two examples of thermodynamic quantities which are not state functions.

Accepted Answer

The answer of a. Explain fully what is meant by...

Question 5

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?

Accepted Answer

A)   5.0 × 10-1 kJ
B)   29 kJ
C)   5.0 × 102 kJ
D)   1.2 × 103 kJ
E)   5.0 × 105 kJ

Question 6

Different chemical bonds have different potential energies.

Accepted Answer

A) True 
 B)False

Question 7

Sand is converted to pure silicon in a three step process. The third step is 
SiCl4(g) + 2Mg(s) F1F1F1S1F1F1F10 2MgCl2(s) + Si(s) F1F1F1S1F1F1F10H = -625.6 kJ
What is the enthalpy change when 25.0 mol of silicon tetrachloride is converted to elemental silicon?

Accepted Answer

A)   -25.0 kJ
B)   -7820 kJ
C)   -1.56 × 104 kJ
D)   -3.13 × 104 kJ
E)   none of the above

Question 8

For a reaction in a sealed, rigid container, F1F1F1S1F1F1F10H is always greater than F1F1F1S1F1F1F10E.

Accepted Answer

A) True 
 B)False

Question 9

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·K) and that the densities of the reactant solutions are both 1.00 g/mL.

Accepted Answer

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

Question 10

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, F1F1F1S1F1F1F10Hf°, in kJ/mol. The formation reaction for ammonia is: 0.5N2(g) + 1.5H2(g) F1F1F1S1F1F1F10 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

Question 11

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 12

The highly exothermic thermite reaction, in which aluminum reduces iron(III) oxide to elemental iron, has been used by railroad repair crews to weld rails together. 
2Al(s) + Fe2O3(s) F1F1F1S1F1F1F10 2Fe(s) + Al2O3(s) F1F1F1S1F1F1F10H = -850 kJ
What mass of iron is formed when 725 kJ of heat are released?

Accepted Answer

A)   47 g
B)   65 g
C)   95 g
D)   112 g
E)   130 g

Question 13

Calculate the F1F1F1S1F1F1F10H°rxn for the following reaction. (F1F1F1S1F1F1F10H°f [AsH3(g)] = 66.4 kJ/mol; F1F1F1S1F1F1F10H°f [H3AsO4(aq)] = -904.6 kJ/mol; F1F1F1S1F1F1F10H°f [H2O(l)] = -285.8 kJ/mol) 
H3AsO4(aq) + 4H2(g) F1F1F1S1F1F1F10 AsH3(g) + 4H2O(l)

Accepted Answer

A)   -1981.4 kJ
B)   -685.2 kJ
C)   -172.2 kJ
D)   172.2 kJ
E)   685.2 kJ

Question 14

For which one of the following reactions will F1F1F1S1F1F1F10H be approximately (or exactly) equal to F1F1F1S1F1F1F10E?

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)

Question 15

Galena is the ore from which elemental lead is extracted. In the first step of the extraction process, galena is heated in air to form lead(II) oxide.
 2PbS(s) + 3O2(g) F1F1F1S1F1F1F10 2PbO(s) + 2SO2(g) F1F1F1S1F1F1F10H = -827.4 kJ
What mass of galena is converted to lead oxide if 975 kJ of heat are liberated?

Accepted Answer

A)   203 g
B)   282 g
C)   406 g
D)   478 g
E)   564 g

Question 16

Calculate the F1F1F1S1F1F1F10H°rxn for the following reaction. (F1F1F1S1F1F1F10H°f [SiO2(s)] = -910.9 kJ/mol; F1F1F1S1F1F1F10H°f [SiCl4(g)] = -657.0 kJ/mol; F1F1F1S1F1F1F10H°f [HCl(g)] = -92.3 kJ/mol; F1F1F1S1F1F1F10H°f [H2O (g)] = -241.8 kJ/mol) SiO2(s) + 4HCl(g) F1F1F1S1F1F1F10 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

Question 17

Two solutions (the system), each of 25.0 mL volume and 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 one of the following relationships concerning the change from initial to final states (both at 25.0°C) is correct?

Accepted Answer

A)   .E = 0
B)   .H = 0
C)   .E > 0
D)   q = 0
E)   w = 0

Question 18

Calculate, in J, the work done by 10.0 g of CO₂ when it sublimes against a pressure of 1.00 atm to form gaseous CO₂ at 0.0°C. The volume of CO₂(s) can be neglected; CO₂(g) can be assumed to behave ideally. The process occurring is CO₂(s) F1F1F1S1F1F1F10 CO₂(g)

Accepted Answer

The answer of Calculate, in J, the work done by...

Question 19

A backpacker collects snow at 0°C, and places it in a cooking pot on a camp stove. It takes 643 kJ of heat energy to melt the snow and bring the water to boiling. Assuming no heat loss, and neglecting the specific heat capacity of the pot, calculate the mass of snow that the backpacker collected. (Data: specific heat capacity of liquid water, c = 4.18 J/gF1F1F1S1F1F1F10K; and: H2O(s) F1F1F1S1F1F1F10 H2O(l) F1F1F1S1F1F1F10H = F1F1F1S1F1F1F10Hfusion = 6.02 kJ/mol)

Accepted Answer

A)   1.92 kg
B)   1.90 kg
C)   1.52 kg
D)   855 g
E)   < 800 g

Question 20

In which one of the following reactions would you expect F1F1F1S1F1F1F10H to be substantially greater than F1F1F1S1F1F1F10E (i.e., F1F1F1S1F1F1F10H > F1F1F1S1F1F1F10E)?

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)

Exam 6: Thermochemistry: Energy Flow and Chemical Change

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 0.800 atm. The value of w, in J, is

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

Consider the equation E = q + w Explain fully the meaning of all three terms in the equation, and also the implied sign convention for q and w.

a. Explain fully what is meant by the term "state function." b. (i) Give two examples of thermodynamic quantities which state functions. (ii) Give two examples of thermodynamic quantities which are not state functions.

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?

Different chemical bonds have different potential energies.

Sand is converted to pure silicon in a three step process. The third step is SiCl₄(g) + 2Mg(s)  2MgCl₂(s) + Si(s) H = -625.6 kJ What is the enthalpy change when 25.0 mol of silicon tetrachloride is converted to elemental silicon?

For a reaction in a sealed, rigid container, H is always greater than E.

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

The highly exothermic thermite reaction, in which aluminum reduces iron(III) oxide to elemental iron, has been used by railroad repair crews to weld rails together. 2Al(s) + Fe₂O₃(s)  2Fe(s) + Al₂O₃(s) H = -850 kJ What mass of iron is formed when 725 kJ of heat are released?

Calculate the H°_rxn for the following reaction. (H°_f [AsH₃(g) ] = 66.4 kJ/mol; H°_f [H₃AsO₄(aq) ] = -904.6 kJ/mol; H°_f [H₂O(l) ] = -285.8 kJ/mol) H₃AsO₄(aq) + 4H₂(g)  AsH₃(g) + 4H₂O(l)

For which one of the following reactions will H be approximately (or exactly) equal to E?

Galena is the ore from which elemental lead is extracted. In the first step of the extraction process, galena is heated in air to form lead(II) oxide. 2PbS(s) + 3O₂(g)  2PbO(s) + 2SO₂(g) H = -827.4 kJ What mass of galena is converted to lead oxide if 975 kJ of heat are liberated?

Calculate the H°_rxn for the following reaction. (H°_f [SiO₂(s) ] = -910.9 kJ/mol; H°_f [SiCl₄(g) ] = -657.0 kJ/mol; H°_f [HCl(g) ] = -92.3 kJ/mol; H°_f [H₂O (g) ] = -241.8 kJ/mol) SiO₂(s) + 4HCl(g)  SiCl₄(g) + 2H₂O(g)

Calculate, in J, the work done by 10.0 g of CO₂ when it sublimes against a pressure of 1.00 atm to form gaseous CO₂ at 0.0°C. The volume of CO₂(s) can be neglected; CO₂(g) can be assumed to behave ideally. The process occurring is CO₂(s)  CO₂(g)

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

Exam 6: Thermochemistry: Energy Flow and Chemical Change

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 0.800 atm. The value of w, in J, is

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

Consider the equation E = q + w Explain fully the meaning of all three terms in the equation, and also the implied sign convention for q and w.

a. Explain fully what is meant by the term "state function." b. (i) Give two examples of thermodynamic quantities which state functions. (ii) Give two examples of thermodynamic quantities which are not state functions.

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?

Different chemical bonds have different potential energies.

Sand is converted to pure silicon in a three step process. The third step is SiCl4(g) + 2Mg(s)  2MgCl2(s) + Si(s) H = -625.6 kJ What is the enthalpy change when 25.0 mol of silicon tetrachloride is converted to elemental silicon?

For a reaction in a sealed, rigid container, H is always greater than E.

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

The highly exothermic thermite reaction, in which aluminum reduces iron(III) oxide to elemental iron, has been used by railroad repair crews to weld rails together. 2Al(s) + Fe2O3(s)  2Fe(s) + Al2O3(s) H = -850 kJ What mass of iron is formed when 725 kJ of heat are released?

Calculate the H°rxn for the following reaction. (H°f [AsH3(g) ] = 66.4 kJ/mol; H°f [H3AsO4(aq) ] = -904.6 kJ/mol; H°f [H2O(l) ] = -285.8 kJ/mol) H3AsO4(aq) + 4H2(g)  AsH3(g) + 4H2O(l)

For which one of the following reactions will H be approximately (or exactly) equal to E?

Galena is the ore from which elemental lead is extracted. In the first step of the extraction process, galena is heated in air to form lead(II) oxide. 2PbS(s) + 3O2(g)  2PbO(s) + 2SO2(g) H = -827.4 kJ What mass of galena is converted to lead oxide if 975 kJ of heat are liberated?

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

Calculate, in J, the work done by 10.0 g of CO2 when it sublimes against a pressure of 1.00 atm to form gaseous CO2 at 0.0°C. The volume of CO2(s) can be neglected; CO2(g) can be assumed to behave ideally. The process occurring is CO2(s)  CO2(g)

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

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?

Sand is converted to pure silicon in a three step process. The third step is SiCl₄(g) + 2Mg(s)  2MgCl₂(s) + Si(s) H = -625.6 kJ What is the enthalpy change when 25.0 mol of silicon tetrachloride is converted to elemental silicon?

The highly exothermic thermite reaction, in which aluminum reduces iron(III) oxide to elemental iron, has been used by railroad repair crews to weld rails together. 2Al(s) + Fe₂O₃(s)  2Fe(s) + Al₂O₃(s) H = -850 kJ What mass of iron is formed when 725 kJ of heat are released?

Calculate the H°_rxn for the following reaction. (H°_f [AsH₃(g) ] = 66.4 kJ/mol; H°_f [H₃AsO₄(aq) ] = -904.6 kJ/mol; H°_f [H₂O(l) ] = -285.8 kJ/mol) H₃AsO₄(aq) + 4H₂(g)  AsH₃(g) + 4H₂O(l)

Galena is the ore from which elemental lead is extracted. In the first step of the extraction process, galena is heated in air to form lead(II) oxide. 2PbS(s) + 3O₂(g)  2PbO(s) + 2SO₂(g) H = -827.4 kJ What mass of galena is converted to lead oxide if 975 kJ of heat are liberated?

Calculate the H°_rxn for the following reaction. (H°_f [SiO₂(s) ] = -910.9 kJ/mol; H°_f [SiCl₄(g) ] = -657.0 kJ/mol; H°_f [HCl(g) ] = -92.3 kJ/mol; H°_f [H₂O (g) ] = -241.8 kJ/mol) SiO₂(s) + 4HCl(g)  SiCl₄(g) + 2H₂O(g)

Calculate, in J, the work done by 10.0 g of CO₂ when it sublimes against a pressure of 1.00 atm to form gaseous CO₂ at 0.0°C. The volume of CO₂(s) can be neglected; CO₂(g) can be assumed to behave ideally. The process occurring is CO₂(s)  CO₂(g)