Question 1

Consider a reaction that has a positive ΔH and a negative ΔS.Which of the following statements is TRUE?

Accepted Answer

The answer of Consider a reaction that has a positive...

Question 2

Calculate ΔS°_rxn for the following reaction.The S° for each species is shown below the reaction. 4 NH₃(g)+ 5 O₂(g)→ 4 NO(g)+ 6 H₂O(g) S°(J/mol^∙K)192.8 205.2 210.8 188.8

Accepted Answer

The answer of Calculate ΔS°_rxn for the following reaction.The S°...

Question 3

Calculate ∆S°_rxn for the following reaction.The S° for each species is shown below the reaction. P₄(g)+ 10 Cl₂(g)→ 4 PCl₅(g) S°(J/mol^∙K)280.0 223.1 364.6

Accepted Answer

∆S°rxn = ∆S°products - ∆S°reactants = (4 mol x 223.1 J/K) - (1 mol x 280.0 J/K + 10 mol x 223.1 J/K) = -1052.6 J/K ∆S°_rxn = ∆S°rxn / n where n is the number of moles of the reaction. n = 1 (for the given reaction) ∆S°_rxn = -1052.6 J/K / 1 mol = -1052.6 J/K Therefore, the answer is B.

Question 4

For the following example,identify the following. H₂O(l)→ H₂O(g)

Accepted Answer

The process of liquid water turning into water vapor (evaporation) requires energy input (endothermic), resulting in a positive ΔH, and increases disorder, resulting in a positive ΔS.

Question 5

Calculate ΔS°_rxn for the following reaction.The S^∘for each species is shown below the reaction. C₂H₂(g)+ 2 H₂(g)→ C₂H₆(g) S°(J/mol^∙K)200.9 130.7 229.2

Accepted Answer

ΔS°rxn = ΣnS°products - ΣnS°reactants ΔS°_rxn = (2 mol)(130.7 J/K) + (1 mol)(200.9 J/K) - (1 mol)(229.2 J/K) - (2 mol)(130.7 J/K) = -233.1 J/K Therefore, the answer is D.

Question 6

Consider a reaction that has a positive ΔH and a positive ΔS.Which of the following statements is TRUE?

Accepted Answer

For a reaction with positive ΔH (endothermic) and positive ΔS (increase in entropy), the spontaneity depends on the temperature according to the Gibbs free energy equation ΔG = ΔH - TΔS. The reaction becomes spontaneous (ΔG < 0) at high temperatures where the TΔS term can overcome the positive ΔH, making ΔG negative.

Question 7

Above what temperature does the following reaction become nonspontaneous? 2 H₂S(g)+ 3 O₂(g)→ 2 SO₂(g)+ 2 H₂O(g)ΔH = -1036 kJ; ΔS = -153.2 J/K

Accepted Answer

The spontaneity of a reaction is determined by the sign of ΔG, which is given by the equation:

ΔG = ΔH - TΔS

where ΔH is the enthalpy change, ΔS is the entropy change, and T is the temperature in Kelvin. The reaction is spontaneous when ΔG is negative and nonspontaneous when ΔG is positive.

To determine the temperature at which the reaction becomes nonspontaneous, we need to find the temperature at which ΔG changes sign, i.e. when ΔG = 0. We can rearrange the equation above to solve for T:

T = ΔH/ΔS

Plugging in the values given in the problem, we get:

T = (-1036 kJ)/(153.2 J/K) = -6.762 × 10^13 K

This answer doesn't make sense because temperature cannot be negative. However, we can see that the sign of ΔH is negative and the sign of ΔS is also negative. This means that the reaction will always have a negative ΔG and thus be spontaneous at all temperatures. Therefore, the answer is E.

Question 8

Which of the following statements is TRUE?

Accepted Answer

Endothermic processes absorb heat from the surroundings, which decreases the entropy of the surroundings at constant temperature and pressure.

Question 9

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 = ΣnΔS°products - ΣmΔS°reactants
ΔS°rxn = (1 mol)(219.3 J/K) + (1 mol)(130.7 J/K) - (1 mol)(200.9 J/K) - (1 mol)(130.7 J/K)
ΔS°rxn = 18.0 J/K
Since there is only one mole of reactant and product, ΔS°S1U1B1rxnS1U1B0 is the same as ΔS°rxn, which is positive (+18.0 J/K). 
To find ΔS°S1U1B1rxnS1U1B1, we need to use the equation:
ΔS°S1U1B1rxnS1U1B1 = ΔS°S1U1B1rxnS1U1B0 + Rln(Q)
where Q = 1 atm (standard state conditions)
and R = 8.31 J/(mol*K)
ΔS°S1U1B1rxnS1U1B1 = 18.0 J/K + (8.31 J/(mol*K))(ln(1 atm))
ΔS°S1U1B1rxnS1U1B1 = 18.0 J/K + 0 J/K
ΔS°S1U1B1rxnS1U1B1 = 18.0 J/K
To find ΔS°S1U1B1rxnS1U1B0, we use the equation:
ΔS°S1U1B1rxnS1U1B0 = ΔS°S1U1B1rxnS1U1B1 - Rln(K)
where K is the equilibrium constant.
Since K = [CS1U1B12S1U1B0HS1U1B14S1U1B0]/[HS1U1B12S1U1B0] and the initial concentration of each species is 1 atm, we can calculate 
K = (1 atm)/(1 atm) = 1
ΔS°S1U1B1rxnS1U1B0 = 18.0 J/K - (8.31 J/(mol*K))(ln(1))
ΔS°S1U1B1rxnS1U1B0 = 18.0 J/K - 0 J/K
ΔS°S1U1B1rxnS1U1B0 = 18.0 J/K
Therefore, ΔS°S1U1B1rxnS1U1B0 = ΔS°rxn = 18.0 J/K, which is positive, so the best choice is (C).

Question 10

For the following example,identify the following. H₂O(l)→ H₂O(s)

Accepted Answer

The change from liquid to solid indicates a decrease in entropy (negative ΔS). Additionally, if the process is spontaneous (i.e. occurs without the input of external energy), then the overall change in energy (enthalpy and entropy) must be negative (ΔG = ΔH - TΔS); therefore, a negative ΔH is also required.

Question 11

Consider a reaction that has a negative ΔH and a negative ΔS.Which of the following statements is TRUE?

Accepted Answer

For a reaction with negative ΔH (enthalpy) and negative ΔS (entropy), the spontaneity depends on the temperature according to the Gibbs free energy equation ΔG = ΔH - TΔS. At low temperatures, the TΔS term will be small, making ΔG negative (indicating spontaneity). At high temperatures, the negative TΔS term will dominate, making ΔG positive (indicating non-spontaneity).

Question 12

Consider a reaction that has a negative ΔH and a positive ΔS.Which of the following statements is TRUE?

Accepted Answer

A negative ΔH indicates an exothermic reaction (releases heat), while a positive ΔS indicates an increase in disorder (entropy) of the system. The combination of these two factors favors spontaneous reactions at all temperatures. Spontaneous means that the reaction can proceed without the need for external energy input.

Question 13

Calculate ΔS°_rxn for the following reaction.The S° for each species is shown below the reaction. N₂H₄(l)+ H₂(g)→ 2 NH₃(g) S° (J/mol^∙K)121.2 130.7 192.8

Accepted Answer

The answer of Calculate ΔS°_rxn for the following reaction.The S°...

Question 14

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 15

What is the sign of ΔS_univ for a biological system?

Accepted Answer

For a biological system, the Δ_univ is likely to be positive, meaning that there is an increase in entropy. Biological systems tend to become more disordered over time, leading to an increase in entropy. Therefore, the sign of the change in entropy is usually positive.

Question 16

Consider a reaction that has a negative ΔH and a negative ΔS.Which of the following statements is TRUE?

Accepted Answer

A negative ΔH means the reaction is exothermic, while a negative ΔS means there is a decrease in the randomness of the system. At low temperatures, the negative entropy change dominates so the reaction is nonspontaneous (i.e., ΔG = ΔH - TΔS is positive). However, as the temperature increases, the positive temperature dependence of the entropy term starts to dominate, eventually making ΔG negative and the reaction spontaneous. Therefore, this reaction will be nonspontaneous only at high temperatures.

Question 17

Which of the following statements is TRUE?

Accepted Answer

Entropy is an extensive property, meaning it depends on the amount of substance present. For example, the entropy of a gas in a container will increase if the volume of the container is increased, as there is now more space for the particles to move around in.

Question 18

Which of the following relationships is correct at constant T and P?

Accepted Answer

At constant temperature and pressure, the change in Gibbs free energy (ΔG) is related to the change in the entropy of the universe (ΔSuniv) by the equation ΔG = -TΔSuniv, where T is the temperature. This relationship indicates that a process is spontaneous if it increases the overall entropy of the universe, which corresponds to ΔG being negative, not positive as suggested by options B and D. ΔG does not directly represent a change in kinetic energy, which eliminates option C. Therefore, only option A correctly describes the relationship between ΔG and the entropy of the universe at constant temperature and pressure.

Question 19

Calculate ∆S°_rxn for the following reaction.The S° for each species is shown below the reaction. 2NO(g)+ 2 H₂(g)→ N₂(g)+ 2 H₂O(l) S°(J/mol^∙K)210.8 130.7 191.6 69.9

Accepted Answer

The answer of Calculate ∆S°_rxn for the following reaction.The S°...

Question 20

Consider a reaction that has a positive ΔH and a positive ΔS.Which of the following statements is TRUE?

Accepted Answer

A positive ΔH means the reaction is endothermic, which is unfavorable for spontaneity. A positive ΔS means the entropy of the system is increasing, which is favorable for spontaneity. At high temperatures, the positive ΔS term dominates, making the reaction spontaneous. However, at low temperatures, the positive ΔH term dominates and makes the reaction nonspontaneous. Therefore, the reaction will be nonspontaneous only at low temperatures.

Quiz 19: Free Energy and Thermodynamics

Consider a reaction that has a positive ΔH and a negative ΔS.Which of the following statements is TRUE?

Calculate ΔS°_rxn for the following reaction.The S° for each species is shown below the reaction. 4 NH₃(g) + 5 O₂(g) → 4 NO(g) + 6 H₂O(g) S°(J/mol^∙K) 192.8 205.2 210.8 188.8

Calculate ∆S°_rxn for the following reaction.The S° for each species is shown below the reaction. P₄(g) + 10 Cl₂(g) → 4 PCl₅(g) S°(J/mol^∙K) 280.0 223.1 364.6

For the following example,identify the following. H₂O(l) → H₂O(g)

Calculate ΔS°_rxn for the following reaction.The S^∘for each species is shown below the reaction. C₂H₂(g) + 2 H₂(g) → C₂H₆(g) S°(J/mol^∙K) 200.9 130.7 229.2

Consider a reaction that has a positive ΔH and a positive ΔS.Which of the following statements is TRUE?

Above what temperature does the following reaction become nonspontaneous? 2 H₂S(g) + 3 O₂(g) → 2 SO₂(g) + 2 H₂O(g) ΔH = -1036 kJ; ΔS = -153.2 J/K

Which of the following statements is TRUE?

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

For the following example,identify the following. H₂O(l) → H₂O(s)

Consider a reaction that has a negative ΔH and a negative ΔS.Which of the following statements is TRUE?

Consider a reaction that has a negative ΔH and a positive ΔS.Which of the following statements is TRUE?

Calculate ΔS°_rxn for the following reaction.The S° for each species is shown below the reaction. N₂H₄(l) + H₂(g) → 2 NH₃(g) S° (J/mol^∙K) 121.2 130.7 192.8

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

What is the sign of ΔS_univ for a biological system?

Consider a reaction that has a negative ΔH and a negative ΔS.Which of the following statements is TRUE?

Which of the following statements is TRUE?

Which of the following relationships is correct at constant T and P?

Calculate ∆S°_rxn for the following reaction.The S° for each species is shown below the reaction. 2NO(g) + 2 H₂(g) → N₂(g) + 2 H₂O(l) S°(J/mol^∙K) 210.8 130.7 191.6 69.9

Consider a reaction that has a positive ΔH and a positive ΔS.Which of the following statements is TRUE?

Quiz 19: Free Energy and Thermodynamics

Consider a reaction that has a positive ΔH and a negative ΔS.Which of the following statements is TRUE?

Calculate ΔS°rxn for the following reaction.The S° for each species is shown below the reaction. 4 NH3(g) + 5 O2(g) → 4 NO(g) + 6 H2O(g) S°(J/mol∙K) 192.8 205.2 210.8 188.8

Calculate ∆S°rxn for the following reaction.The S° for each species is shown below the reaction. P4(g) + 10 Cl2(g) → 4 PCl5(g) S°(J/mol∙K) 280.0 223.1 364.6

For the following example,identify the following. H2O(l) → H2O(g)

Calculate ΔS°rxn for the following reaction.The S∘ for each species is shown below the reaction. C2H2(g) + 2 H2(g) → C2H6(g) S°(J/mol∙K) 200.9 130.7 229.2

Consider a reaction that has a positive ΔH and a positive ΔS.Which of the following statements is TRUE?

Above what temperature does the following reaction become nonspontaneous? 2 H2S(g) + 3 O2(g) → 2 SO2(g) + 2 H2O(g) ΔH = -1036 kJ; ΔS = -153.2 J/K

Which of the following statements is TRUE?

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

For the following example,identify the following. H2O(l) → H2O(s)

Consider a reaction that has a negative ΔH and a negative ΔS.Which of the following statements is TRUE?

Consider a reaction that has a negative ΔH and a positive ΔS.Which of the following statements is TRUE?

Calculate ΔS°rxn for the following reaction.The S° for each species is shown below the reaction. N2H4(l) + H2(g) → 2 NH3(g) S° (J/mol∙K) 121.2 130.7 192.8

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

What is the sign of ΔSuniv for a biological system?

Consider a reaction that has a negative ΔH and a negative ΔS.Which of the following statements is TRUE?

Which of the following statements is TRUE?

Which of the following relationships is correct at constant T and P?

Calculate ∆S°rxn for the following reaction.The S° for each species is shown below the reaction. 2NO(g) + 2 H2(g) → N2(g) + 2 H2O(l) S°(J/mol∙K) 210.8 130.7 191.6 69.9

Consider a reaction that has a positive ΔH and a positive ΔS.Which of the following statements is TRUE?

Calculate ΔS°_rxn for the following reaction.The S° for each species is shown below the reaction. 4 NH₃(g) + 5 O₂(g) → 4 NO(g) + 6 H₂O(g) S°(J/mol^∙K) 192.8 205.2 210.8 188.8

Calculate ∆S°_rxn for the following reaction.The S° for each species is shown below the reaction. P₄(g) + 10 Cl₂(g) → 4 PCl₅(g) S°(J/mol^∙K) 280.0 223.1 364.6

For the following example,identify the following. H₂O(l) → H₂O(g)

Calculate ΔS°_rxn for the following reaction.The S^∘for each species is shown below the reaction. C₂H₂(g) + 2 H₂(g) → C₂H₆(g) S°(J/mol^∙K) 200.9 130.7 229.2

Above what temperature does the following reaction become nonspontaneous? 2 H₂S(g) + 3 O₂(g) → 2 SO₂(g) + 2 H₂O(g) ΔH = -1036 kJ; ΔS = -153.2 J/K

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

For the following example,identify the following. H₂O(l) → H₂O(s)

Calculate ΔS°_rxn for the following reaction.The S° for each species is shown below the reaction. N₂H₄(l) + H₂(g) → 2 NH₃(g) S° (J/mol^∙K) 121.2 130.7 192.8

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

What is the sign of ΔS_univ for a biological system?

Calculate ∆S°_rxn for the following reaction.The S° for each species is shown below the reaction. 2NO(g) + 2 H₂(g) → N₂(g) + 2 H₂O(l) S°(J/mol^∙K) 210.8 130.7 191.6 69.9