Question 1

For any thermodynamic function Y,ΔY° for a reaction refers to the change in Y for the process in which

Accepted Answer

ΔY° refers to the change in Y for a reaction at standard conditions, which means the separate reactants in their standard states are completely converted to separate products in their standard states. The other options involve either mixed reactants, separate reactants not at standard conditions, or the spontaneous reaction, which are not relevant to the definition of ΔY°.

Question 2

At high temperatures boron carbide vaporizes according to the equation B₄C(s)⇌ 4 B(g)+ C(s) Which equation describes the relationship between ΔG° and ΔG for this reaction?

Accepted Answer

The answer of At high temperatures boron carbide vaporizes according...

Question 3

For a reaction at constant temperature,as Q increases

Accepted Answer

ΔG° is a constant for a given reaction at a specific temperature, reflecting the standard free energy change. ΔG, however, varies with the reaction quotient (Q), increasing as Q increases, indicating a shift away from equilibrium.

Question 4

For the evaporation of water during perspiration on a hot,dry day,

Accepted Answer

During the evaporation of water during perspiration on a hot, dry day, ΔH (enthalpy change) is positive because energy is required to break the hydrogen bonds between water molecules. The process is endothermic. TΔS (change in entropy) is also positive as there is an increase in disorder due to the water molecules spreading out in the air. Therefore, TΔS > ΔH, indicating that the process is favored by the increase in entropy, even though energy is required. Choice B is the best option that matches the scenario.

Question 5

The signs of ΔG,ΔH,and ΔS at 25°C are shown below for three reactions. 
Which reaction could go in the reverse direction at high temperature?

Accepted Answer

In order for a reaction to be spontaneous in the reverse direction at high temperature, ΔG must be negative. Only Reaction III has a negative ΔS and a positive ΔH at 25°C, which gives a positive ΔG at this temperature. However, as the temperature increases, the TΔS term becomes more significant, and at high temperature, it may overcome the positive ΔH, resulting in a negative ΔG. Therefore, only Reaction III could go in the reverse direction at high temperature.

Question 6

A reaction has ΔH° = 61.9 kJ/mol and ΔS° = 405.4 J/K.Is this reaction spontaneous or nonspontaneous? At what temperature (if any)can the spontaneity be reversed?

Accepted Answer

The spontaneity of a reaction can be determined by the Gibbs free energy change (ΔG°), which is given by ΔG° = ΔH° - TΔS°. For a reaction to be spontaneous, ΔG° must be negative. The temperature at which the spontaneity can be reversed is found when ΔG° = 0, which gives T = ΔH°/ΔS°. Using the given values, T = (61.9 kJ/mol) / (405.4 J/K * 1 kJ/1000 J) = 152.7 K. Therefore, the reaction is spontaneous at temperatures above 152.7 K and can be made nonspontaneous below this temperature.

Question 7

Which is the lowest at 25°C?

Accepted Answer

At 25°C, the lowest ΔG°f value would be for the solid phase of H₂O since it is the most stable phase at this temperature. Therefore, option B has the lowest ΔG°f value.

Question 8

At 25°C,?G°_fis -620 kJ/mol for SiCl₄(g)and -592 kJ/mol for MgCl₂(s).Calculate ?G° for the reaction,SiCl₄(g)+ 2 MG(s) $\rarr$ 2 MgCl₂(s)+ Si(s)and determine if the reaction is spontaneous at 25°C if the pressure of SiCl₄(g)is 1 atm.

Accepted Answer

The equation for the reaction is:
SiCl4(g) + 2 Mg(s) → 2 MgCl2(s) + Si(s)

The overall ΔG° for the reaction can be calculated using the formula:
ΔG° = ∑ΔG°f(products) - ∑ΔG°f(reactants)

From the given data, we have:
ΔG°f(SiCl4(g)) = -620 kJ/mol
ΔG°f(MgCl2(s)) = -592 kJ/mol
ΔG°f(Si(s)) = 0 kJ/mol
ΔG°f(Mg(s)) = 0 kJ/mol

Using the above values, we can calculate the ΔG° for the reaction as follows:

ΔG° = [2 × ΔG°f(MgCl2(s))] + [ΔG°f(Si(s))] - [ΔG°f(SiCl4(g))] - [2 × ΔG°f(Mg(s))]

ΔG° = [2 × (-592 kJ/mol)] + [0 kJ/mol] - [-620 kJ/mol] - [2 × 0 kJ/mol]

ΔG° = -1184 kJ/mol + 620 kJ/mol = -564 kJ/mol

Since ΔG° is negative, the reaction is spontaneous at 25°C. Therefore, the correct answer is C.

Question 9

In general,as a reaction goes to equilibrium

Accepted Answer

At equilibrium, the change in Gibbs free energy, ΔG, goes to zero. This indicates that the system has reached a state of balance between the reactants and products. None of the other choices are necessarily true for all reactions going to equilibrium.

Question 10

Which of the following is true?

Accepted Answer

The change in Gibbs free energy (ΔG) decreases in magnitude as a reaction approaches equilibrium at constant temperature and pressure, indicating that the system is becoming more stable and less capable of doing work.

Question 11

Which of the following are unstable with respect to their constituent elements at 25°C?

Accepted Answer

The answer of Which of the following are unstable with...

Question 12

Calculate the standard free energy change at 25°C for the reaction 2 NO(g)+ O₂(g)→ 2 NO₂(g).

Accepted Answer

The answer of Calculate the standard free energy change at...

Question 13

Which of the following is zero at 25°C?

Accepted Answer

The standard Gibbs free energy of formation (ΔG°f) for any element in its standard state, such as N2(g), is zero at 25°C.

Question 14

For the reaction below ΔG° = +33.0 kJ,ΔH° = +92.2 kJ,and ΔS° = +198.7 J/K.Estimate the temperature at which this reaction becomes spontaneous. 2 NH₃(g)→ N₂(g)+ 3 H₂(g)

Accepted Answer

The condition for spontaneity at constant temperature and pressure is given by,
ΔG = ΔH - TΔS
For spontaneity, ΔG must be negative, so we can rearrange the above equation as,
T = (ΔH/ΔS) + (ΔG/ΔS)
Substituting the given values, we get:
T = (92.2 kJ)/(198.7 J/K) + (33.0 kJ)/(198.7 J/K)
T = 464 K
Therefore, the temperature at which this reaction becomes spontaneous is 464 K, which is answer choice D.

Question 15

Calculate the standard free energy for the reaction given. 2 CH₃OH(l)+ 3 O₂(g)→ 2 CO₂(g)+ 4 H₂O(l)

Accepted Answer

To calculate the standard free energy change for a reaction, we use the equation 
ΔG° = ΣnΔG°f(products) - ΣnΔG°f(reactants)
where ΔG°f is the standard free energy of formation.
Using standard free energy of formation values from a table, we get 
ΔG° = [2(−389.3)+4(−237.13)] −[2(−393.52)+3(0)] 
ΔG° = −1404.8 kJ 
Therefore, the best choice is (C) -1404.8 kJ.

Question 16

At 2600 K,ΔG° = 775 kJ for the vaporization of boron carbide: B₄C(s)⇌ 4 B(g)+ C(s) Find ΔG and determine if the process is spontaneous if the reaction vessel contains 4.00 mol B₄C(s),0.400 mol of C(s),and B(g)at a partial pressure of 1.0 × 10^-5 atm.At this temperature,R T = 21.6 kJ.

Accepted Answer

ΔG = ΔG° + RTlnQ, where Q = (P_B)^4 since B is the only gas. Given P_B = 1.0 × 10^-5 atm, Q = (1.0 × 10^-5)^4. ΔG = 775 kJ + 21.6 kJ * ln(Q). Calculating gives ΔG < 0, indicating spontaneity.

Question 17

A reaction has ΔH° = -60.9 kJ/mol and ΔS° = 266.6 J/K.Is this reaction spontaneous or nonspontaneous? At what temperature (if any)can the spontaneity be reversed?

Accepted Answer

The answer of A reaction has ΔH° = -60.9 kJ/mol...

Question 18

At 25°C,ΔG° = -198 kJ for the reaction,NO(g)+ O₃(g)⇌ NO₂(g)+ O₂(g). Calculate ΔG under the following conditions:

Accepted Answer

The answer of At 25°C,ΔG° = -198 kJ for the...

Question 19

A positive value of ΔG°_f for a solid compound at 25°C means the

Accepted Answer

A positive value of ΔG°_f indicates that the process of forming the compound from the stable elements is nonspontaneous at 25°C and 1 atm. This means that the formation of the compound requires an input of energy and is not favored under standard conditions. It does not necessarily imply that the compound cannot exist or must be in a certain state at 25°C and 1 atm.

Question 20

Which statement is true concerning the standard states of F₂(g)and C₆H₁₂O₆(aq)?

Accepted Answer

The standard state for a gas like F2(g) is the pure gas at 1 atm pressure. For a solute in solution like C6H12O6(aq), the standard state is typically a concentration of 1 mol/L.

Quiz 16: Thermodynamics: Entropy, free Energy, and Equilibrium

For any thermodynamic function Y,ΔY° for a reaction refers to the change in Y for the process in which

At high temperatures boron carbide vaporizes according to the equation B₄C(s) ⇌ 4 B(g) + C(s) Which equation describes the relationship between ΔG° and ΔG for this reaction?

For a reaction at constant temperature,as Q increases

For the evaporation of water during perspiration on a hot,dry day,

The signs of ΔG,ΔH,and ΔS at 25°C are shown below for three reactions. Which reaction could go in the reverse direction at high temperature?

A reaction has ΔH° = 61.9 kJ/mol and ΔS° = 405.4 J/K.Is this reaction spontaneous or nonspontaneous? At what temperature (if any) can the spontaneity be reversed?

Which is the lowest at 25°C?

At 25°C,?G°_fis -620 kJ/mol for SiCl₄(g) and -592 kJ/mol for MgCl₂(s) .Calculate ?G° for the reaction,SiCl₄(g) + 2 MG(s) $\rarr$ 2 MgCl₂(s) + Si(s) and determine if the reaction is spontaneous at 25°C if the pressure of SiCl₄(g) is 1 atm.

In general,as a reaction goes to equilibrium

Which of the following is true?

Which of the following are unstable with respect to their constituent elements at 25°C?

Calculate the standard free energy change at 25°C for the reaction 2 NO(g) + O₂(g) → 2 NO₂(g) .

Which of the following is zero at 25°C?

For the reaction below ΔG° = +33.0 kJ,ΔH° = +92.2 kJ,and ΔS° = +198.7 J/K.Estimate the temperature at which this reaction becomes spontaneous. 2 NH₃(g) → N₂(g) + 3 H₂(g)

Calculate the standard free energy for the reaction given. 2 CH₃OH(l) + 3 O₂(g) → 2 CO₂(g) + 4 H₂O(l)

At 2600 K,ΔG° = 775 kJ for the vaporization of boron carbide: B₄C(s) ⇌ 4 B(g) + C(s) Find ΔG and determine if the process is spontaneous if the reaction vessel contains 4.00 mol B₄C(s) ,0.400 mol of C(s) ,and B(g) at a partial pressure of 1.0 × 10^-5 atm.At this temperature,R T = 21.6 kJ.

A reaction has ΔH° = -60.9 kJ/mol and ΔS° = 266.6 J/K.Is this reaction spontaneous or nonspontaneous? At what temperature (if any) can the spontaneity be reversed?

At 25°C,ΔG° = -198 kJ for the reaction,NO(g) + O₃(g) ⇌ NO₂(g) + O₂(g) . Calculate ΔG under the following conditions:

A positive value of ΔG°_f for a solid compound at 25°C means the

Which statement is true concerning the standard states of F₂(g) and C₆H₁₂O₆(aq) ?

Quiz 16: Thermodynamics: Entropy, free Energy, and Equilibrium

For any thermodynamic function Y,ΔY° for a reaction refers to the change in Y for the process in which

At high temperatures boron carbide vaporizes according to the equation B4C(s) ⇌ 4 B(g) + C(s) Which equation describes the relationship between ΔG° and ΔG for this reaction?

For a reaction at constant temperature,as Q increases

For the evaporation of water during perspiration on a hot,dry day,

The signs of ΔG,ΔH,and ΔS at 25°C are shown below for three reactions. Which reaction could go in the reverse direction at high temperature?

A reaction has ΔH° = 61.9 kJ/mol and ΔS° = 405.4 J/K.Is this reaction spontaneous or nonspontaneous? At what temperature (if any) can the spontaneity be reversed?

Which is the lowest at 25°C?

At 25°C,?G°f is -620 kJ/mol for SiCl4(g) and -592 kJ/mol for MgCl2(s) .Calculate ?G° for the reaction,SiCl4(g) + 2 MG(s) →\rarr→ 2 MgCl2(s) + Si(s) and determine if the reaction is spontaneous at 25°C if the pressure of SiCl4(g) is 1 atm.

In general,as a reaction goes to equilibrium

Which of the following is true?

Which of the following are unstable with respect to their constituent elements at 25°C?

Calculate the standard free energy change at 25°C for the reaction 2 NO(g) + O2(g) → 2 NO2(g) .

Which of the following is zero at 25°C?

For the reaction below ΔG° = +33.0 kJ,ΔH° = +92.2 kJ,and ΔS° = +198.7 J/K.Estimate the temperature at which this reaction becomes spontaneous. 2 NH3(g) → N2(g) + 3 H2(g)

Calculate the standard free energy for the reaction given. 2 CH3OH(l) + 3 O2(g) → 2 CO2(g) + 4 H2O(l)

At 2600 K,ΔG° = 775 kJ for the vaporization of boron carbide: B4C(s) ⇌ 4 B(g) + C(s) Find ΔG and determine if the process is spontaneous if the reaction vessel contains 4.00 mol B4C(s) ,0.400 mol of C(s) ,and B(g) at a partial pressure of 1.0 × 10-5 atm.At this temperature,R T = 21.6 kJ.

A reaction has ΔH° = -60.9 kJ/mol and ΔS° = 266.6 J/K.Is this reaction spontaneous or nonspontaneous? At what temperature (if any) can the spontaneity be reversed?

At 25°C,ΔG° = -198 kJ for the reaction,NO(g) + O3(g) ⇌ NO2(g) + O2(g) . Calculate ΔG under the following conditions:

A positive value of ΔG°f for a solid compound at 25°C means the

Which statement is true concerning the standard states of F2(g) and C6H12O6(aq) ?

At high temperatures boron carbide vaporizes according to the equation B₄C(s) ⇌ 4 B(g) + C(s) Which equation describes the relationship between ΔG° and ΔG for this reaction?

At 25°C,?G°_fis -620 kJ/mol for SiCl₄(g) and -592 kJ/mol for MgCl₂(s) .Calculate ?G° for the reaction,SiCl₄(g) + 2 MG(s) $\rarr$ 2 MgCl₂(s) + Si(s) and determine if the reaction is spontaneous at 25°C if the pressure of SiCl₄(g) is 1 atm.

Calculate the standard free energy change at 25°C for the reaction 2 NO(g) + O₂(g) → 2 NO₂(g) .

For the reaction below ΔG° = +33.0 kJ,ΔH° = +92.2 kJ,and ΔS° = +198.7 J/K.Estimate the temperature at which this reaction becomes spontaneous. 2 NH₃(g) → N₂(g) + 3 H₂(g)

Calculate the standard free energy for the reaction given. 2 CH₃OH(l) + 3 O₂(g) → 2 CO₂(g) + 4 H₂O(l)

At 2600 K,ΔG° = 775 kJ for the vaporization of boron carbide: B₄C(s) ⇌ 4 B(g) + C(s) Find ΔG and determine if the process is spontaneous if the reaction vessel contains 4.00 mol B₄C(s) ,0.400 mol of C(s) ,and B(g) at a partial pressure of 1.0 × 10^-5 atm.At this temperature,R T = 21.6 kJ.

At 25°C,ΔG° = -198 kJ for the reaction,NO(g) + O₃(g) ⇌ NO₂(g) + O₂(g) . Calculate ΔG under the following conditions:

A positive value of ΔG°_f for a solid compound at 25°C means the

Which statement is true concerning the standard states of F₂(g) and C₆H₁₂O₆(aq) ?