Question 1

Place the following in order of increasing entropy at 298 K. Ne Xe He Ar Kr

Accepted Answer

Entropy generally increases with the size and complexity of the molecule. In this case, all the substances are noble gases, so complexity is not a factor, but size is. Helium (He) is the smallest and xenon (Xe) is the largest, so entropy increases from He to Xe.

Question 2

Given the following equation, N₂O(g)+ NO₂(g)→ 3 NO(g)ΔG°_rxn = -23.0 kJ Calculate ΔG°_rxn for the following reaction. 3 NO(g)→ N₂O(g)+ NO₂(g)

Accepted Answer

The ΔG° for the reverse reaction is the negative of the ΔG° for the forward reaction, making the correct answer 23.0 kJ.

Question 3

Calculate ΔS°_rxn for the following reaction.The S° for each species is shown below the reaction. C₂H₂(g)+ H₂(g)→ C₂H₄(g) S°(J/mol∙K)200.9 130.7 219.3

Accepted Answer

ΔS°rxn can be calculated by adding the products' S° and subtracting the reactants' S°. ΔS°rxn = [(S° CS12H14S - S° CS12H12S) + (S° H2S - S° H2)] = [219.3 - 200.9 + (130.7 - 131.0)] J/mol∙K = -112.3 J/mol∙K. Since ΔS°rxn = ΔS°_rxn, the answer is C.

Question 4

Give the name of the reaction that achieves the theoretical limits with respect to free energy in thermodynamics.

Accepted Answer

The reversible reaction achieves the theoretical limits with respect to free energy as it can proceed in both forward and reverse directions, reaching equilibrium without any net change in free energy. This means that it can achieve both the maximum work and minimum work limits, making it the most efficient reaction in terms of energy.

Question 5

Identify the element with the highest standard free energy of formation.

Accepted Answer

The standard free energy of formation for any element in its standard state, such as the solid forms of Ba, Ca, Li, and K, is defined as zero. This is a convention used in thermodynamics to provide a reference point for calculating the free energies of compounds.

Question 6

Identify the compound with the highest ΔG°_f.

Accepted Answer

The standard Gibbs free energy of formation (ΔG°f) for elements in their standard states is defined as zero. Since all the given compounds (N2, H2, O2, Cl2) are diatomic molecules in their standard gaseous states and represent elemental forms, their ΔG°f values are zero.

Question 7

Place the following in order of decreasing molar entropy at 298 K. H₂ Cl₂ F₂

Accepted Answer

Cl₂ has the highest molar entropy due to its larger molecular size and more complex structure compared to F₂ and H₂. F₂ has a higher molar entropy than H₂ because it is a larger molecule with more electrons, leading to more possible microstates.

Question 8

Calculate the ΔG°_rxn using the following information. 4 HNO₃(g)+ 5 N₂H₄(l)→ 7 N₂(g)+ 12 H₂O(l)ΔG°_rxn= ? ΔH°_f (kJ/mol)-133.9 50.6 -285.8 S°(J/mol∙K)266.9 121.2 191.6 70.0

Accepted Answer

ΔG°_rxn = ΔH°_rxn - TΔS°_rxnΔH°_rxn = [7(-285.8) + 12(-237.1)] - [4(-133.9) + 5(50.6)] = -3.15 × 10³ kJΔS°_rxn = [7(191.6) + 12(70.0)] - [4(266.9) + 5(121.2)] = -105.2 J/mol∙KΔG°_rxn = -3.15 × 10³ kJ - (298 K)(-105.2 J/mol∙K) = -3.30 × 10³ kJ

Question 9

Place the following in order of increasing standard molar entropy. H₂O(l)H₂O(g)H₂O(s)

Accepted Answer

Entropy increases from solid to liquid to gas due to increasing molecular disorder and freedom of movement.

Question 10

Below what temperature does the following reaction become nonspontaneous? 2 HNO₃(aq)+ NO(g)→ 3 NO₂(g)+ H₂O(l)ΔH = +136.5 kJ; ΔS = +287.5 J/K

Accepted Answer

The reaction becomes nonspontaneous when ΔG > 0. Using the equation ΔG = ΔH - TΔS, set ΔG = 0 to find the temperature: 0 = 136500 J - T(287.5 J/K). Solving for T gives T = 136500 / 287.5 = 475 K.

Question 11

The ________ Law of Thermodynamics states the entropy of a perfect crystal at absolute zero is zero.

Accepted Answer

The Third Law of Thermodynamics states that the entropy of a perfect crystal at absolute zero is zero.

Question 12

Place the following in order of decreasing standard molar entropy. N₂O₄(g)NO(g)NO₂(g)

Accepted Answer

Standard molar entropy generally increases with the complexity and size of the molecule, as well as the number of atoms and degrees of freedom (rotational, translational, vibrational). NSO (with the highest molecular complexity and number of atoms) has the highest entropy, followed by NOS, and then NO with the least complexity and fewest atoms.

Question 13

Which one of the following has the highest standard molar entropy,S°,at 25°C?

Accepted Answer

The standard molar entropy, S°, is related to the degree of disorder or randomness of a substance. Since the size of the halide ion increases as you move down the periodic table, the lattice structure of the solid becomes more open and the disorder, or entropy, increases. Therefore, NaI, being the largest and most "disordered" of the halide salts, has the highest standard molar entropy at 25°C.

Question 14

Place the following in order of increasing molar entropy at 298 K. NO CO SO

Accepted Answer

Entropy generally increases with increasing molecular complexity and mass. CO has the lowest molar entropy, followed by NO, and SO has the highest due to its greater molecular complexity and mass.

Question 15

Identify the statement that is FALSE.

Accepted Answer

Free atoms have less entropy than molecules because they have fewer degrees of freedom.

Question 16

Give the name of the reaction that does not achieve the theoretical limits with respect to free energy in thermodynamics.

Accepted Answer

Irreversible reactions do not achieve the theoretical limits with respect to free energy in thermodynamics because they cannot reach equilibrium and proceed in only one direction, leading to a loss of potential energy. Therefore, irreversible reactions have a lower efficiency compared to reversible reactions.

Question 17

What can change the direction of a reversible reaction involving gases?

Accepted Answer

According to Le Chatelier's Principle, a change in temperature, pressure, or volume can shift the equilibrium of a reversible reaction involving gases. Increasing the temperature typically favors the endothermic direction, while decreasing the temperature favors the exothermic direction. An increase in pressure or decrease in volume typically favors the side with fewer moles of gas. A decrease in pressure or increase in volume typically favors the side with more moles of gas. Therefore, all of the above options can change the direction of a reversible reaction involving gases.

Question 18

Above what temperature does the following reaction become nonspontaneous? FeO(s)+ CO(g)→ CO₂(g)+ Fe(s)ΔH = -11.0 kJ; ΔS = -17.4 J/K

Accepted Answer

For a reaction to be spontaneous, the Gibbs free energy change (ΔG) must be negative. The equation ΔG = ΔH - TΔS can be rearranged to solve for the temperature (T) at which ΔG = 0 (the threshold between spontaneity and non-spontaneity): T = ΔH/ΔS. Plugging in the values (ΔH = -11.0 kJ = -11000 J; ΔS = -17.4 J/K), we get T = -11000 J / -17.4 J/K = 632 K. Above this temperature, the reaction becomes nonspontaneous because the positive TΔS term outweighs the negative ΔH, making ΔG positive.

Question 19

Which of the following statements is TRUE?

Accepted Answer

Entropy is an extensive property as its value increases with an increase in the quantity of a system. Answer: E None of the given statements is completely true. Entropy is temperature dependent, exothermic processes can increase the entropy of the surroundings under certain conditions, and ΔS_universe can be negative for a nonspontaneous process under certain conditions.

Question 20

For a given compound,list the decreasing order of entropy for a liquid,solid,and gas.

Accepted Answer

The entropy of a substance generally increases from solid to liquid to gas, because the increase in freedom of motion and number of available states outweighs any decrease in order. Therefore, the decreasing order of entropy for a compound would be gas > liquid > solid. Thus, the correct choice is C.

Quiz 18: Free Energy and Thermodynamics

Place the following in order of increasing entropy at 298 K. Ne Xe He Ar Kr

Given the following equation, N₂O(g) + NO₂(g) → 3 NO(g) ΔG°_rxn = -23.0 kJ Calculate ΔG°_rxn for the following reaction. 3 NO(g) → N₂O(g) + NO₂(g)

Calculate ΔS°_rxn for the following reaction.The S° for each species is shown below the reaction. C₂H₂(g) + H₂(g) → C₂H₄(g) S°(J/mol∙K) 200.9 130.7 219.3

Give the name of the reaction that achieves the theoretical limits with respect to free energy in thermodynamics.

Identify the element with the highest standard free energy of formation.

Identify the compound with the highest ΔG°_f.

Place the following in order of decreasing molar entropy at 298 K. H₂ Cl₂ F₂

Calculate the ΔG°_rxn using the following information. 4 HNO₃(g) + 5 N₂H₄(l) → 7 N₂(g) + 12 H₂O(l) ΔG°_rxn= ? ΔH°_f (kJ/mol) -133.9 50.6 -285.8 S°(J/mol∙K) 266.9 121.2 191.6 70.0

Place the following in order of increasing standard molar entropy. H₂O(l) H₂O(g) H₂O(s)

Below what temperature does the following reaction become nonspontaneous? 2 HNO₃(aq) + NO(g) → 3 NO₂(g) + H₂O(l) ΔH = +136.5 kJ; ΔS = +287.5 J/K

The ________ Law of Thermodynamics states the entropy of a perfect crystal at absolute zero is zero.

Place the following in order of decreasing standard molar entropy. N₂O₄(g) NO(g) NO₂(g)

Which one of the following has the highest standard molar entropy,S°,at 25°C?

Place the following in order of increasing molar entropy at 298 K. NO CO SO

Identify the statement that is FALSE.

Give the name of the reaction that does not achieve the theoretical limits with respect to free energy in thermodynamics.

What can change the direction of a reversible reaction involving gases?

Above what temperature does the following reaction become nonspontaneous? FeO(s) + CO(g) → CO₂(g) + Fe(s) ΔH = -11.0 kJ; ΔS = -17.4 J/K

Which of the following statements is TRUE?

For a given compound,list the decreasing order of entropy for a liquid,solid,and gas.

Quiz 18: Free Energy and Thermodynamics

Place the following in order of increasing entropy at 298 K. Ne Xe He Ar Kr

Given the following equation, N2O(g) + NO2(g) → 3 NO(g) ΔG°rxn = -23.0 kJ Calculate ΔG°rxn for the following reaction. 3 NO(g) → N2O(g) + NO2(g)

Calculate ΔS°rxn for the following reaction.The S° for each species is shown below the reaction. C2H2(g) + H2(g) → C2H4(g) S°(J/mol∙K) 200.9 130.7 219.3

Give the name of the reaction that achieves the theoretical limits with respect to free energy in thermodynamics.

Identify the element with the highest standard free energy of formation.

Identify the compound with the highest ΔG°f.

Place the following in order of decreasing molar entropy at 298 K. H2 Cl2 F2

Calculate the ΔG°rxn using the following information. 4 HNO3(g) + 5 N2H4(l) → 7 N2(g) + 12 H2O(l) ΔG°rxn = ? ΔH°f (kJ/mol) -133.9 50.6 -285.8 S°(J/mol∙K) 266.9 121.2 191.6 70.0

Place the following in order of increasing standard molar entropy. H2O(l) H2O(g) H2O(s)

Below what temperature does the following reaction become nonspontaneous? 2 HNO3(aq) + NO(g) → 3 NO2(g) + H2O(l) ΔH = +136.5 kJ; ΔS = +287.5 J/K

The ________ Law of Thermodynamics states the entropy of a perfect crystal at absolute zero is zero.

Place the following in order of decreasing standard molar entropy. N2O4(g) NO(g) NO2(g)

Which one of the following has the highest standard molar entropy,S°,at 25°C?

Place the following in order of increasing molar entropy at 298 K. NO CO SO

Identify the statement that is FALSE.

Give the name of the reaction that does not achieve the theoretical limits with respect to free energy in thermodynamics.

What can change the direction of a reversible reaction involving gases?

Above what temperature does the following reaction become nonspontaneous? FeO(s) + CO(g) → CO2(g) + Fe(s) ΔH = -11.0 kJ; ΔS = -17.4 J/K

Which of the following statements is TRUE?

For a given compound,list the decreasing order of entropy for a liquid,solid,and gas.

Given the following equation, N₂O(g) + NO₂(g) → 3 NO(g) ΔG°_rxn = -23.0 kJ Calculate ΔG°_rxn for the following reaction. 3 NO(g) → N₂O(g) + NO₂(g)

Calculate ΔS°_rxn for the following reaction.The S° for each species is shown below the reaction. C₂H₂(g) + H₂(g) → C₂H₄(g) S°(J/mol∙K) 200.9 130.7 219.3

Identify the compound with the highest ΔG°_f.

Place the following in order of decreasing molar entropy at 298 K. H₂ Cl₂ F₂

Calculate the ΔG°_rxn using the following information. 4 HNO₃(g) + 5 N₂H₄(l) → 7 N₂(g) + 12 H₂O(l) ΔG°_rxn= ? ΔH°_f (kJ/mol) -133.9 50.6 -285.8 S°(J/mol∙K) 266.9 121.2 191.6 70.0

Place the following in order of increasing standard molar entropy. H₂O(l) H₂O(g) H₂O(s)

Below what temperature does the following reaction become nonspontaneous? 2 HNO₃(aq) + NO(g) → 3 NO₂(g) + H₂O(l) ΔH = +136.5 kJ; ΔS = +287.5 J/K

Place the following in order of decreasing standard molar entropy. N₂O₄(g) NO(g) NO₂(g)

Above what temperature does the following reaction become nonspontaneous? FeO(s) + CO(g) → CO₂(g) + Fe(s) ΔH = -11.0 kJ; ΔS = -17.4 J/K