Question 1

For the reaction PCl₅(g)→ PCl₃(g)+ Cl₂(g)at 298 K,K_eq = 1.87 × 10^-7,what is Δ_rG ° and is the reaction spontaneous? A)3.84 × 10⁴ kJ/mol,no B)7.68 kJ/mol,no C)-7.68 kJ/mol,yes D)38.4 kJ/mol,no E)-38.4 kJ/mol,yes

Accepted Answer

The answer of For the reaction PCl₅(g)→ PCl₃(g)+ Cl₂(g)at 298...

Question 2

A reaction is spontaneous if:
I.ΔG is a negative value
II.both enthalpy and entropy increase
III.ΔH is negative and ΔS is positive
IV.both enthalpy and entropy decrease
V.ΔH is positive and ΔS is negative
A)I and III
B)I and II
C)II and V
D)III and IV
E)II and IV

Accepted Answer

Only I and III are correct statements. ΔG indicates the spontaneity of a reaction, and a negative ΔG value implies that the reaction will proceed spontaneously. However, for a spontaneous reaction, the enthalpy change must be negative (ΔH < 0) to indicate an exothermic reaction and the entropy change must be positive (ΔS > 0) to indicate that the products are more disordered than the reactants. Therefore, statement III is also correct. Statements II, IV, and V are not correct because they present conflicting information or information that is not applicable to the spontaneity of a reaction.

Question 3

The equilibrium constant for the reaction below is 7.2 × 10^-4 at 298 K and 1 atm. HNO₂(aq)+ H₂O(l)⇌ NO₂^-(aq)+ H₃O⁺(aq) When [HNO₂(aq)] = 1.0 M and [NO₂^-(aq)] = [H₃O⁺(aq)] = 1.0 × 10^-5M,calculate ΔG. A)-39.1 kJ/mol B)+17.9 kJ/mol C)-17.9 kJ/mol D)+39.1 kJ/mol E)-23.02 kJ/mol

Accepted Answer

ΔG° = -RTlnK

where K is the equilibrium constant.

R = 8.314 J/mol.K (gas constant), T = 298 K, and K = 7.2 × 10^-4

ΔG° = -8.314 J/mol.K * 298 K * ln(7.2 × 10^-4)

ΔG° = -39.1 kJ/mol

Therefore, the answer is A, -39.1 kJ/mol.

Question 4

The following reaction is exothermic. 2 N₂O(g)→ 2 N₂(g)+ O₂(g) This means the reaction: A)will be spontaneous at all temperatures B)will be spontaneous only at high temperature C)will be spontaneous only at low temperatures D)is not spontaneous at any temperature E)cannot determine without temperature

Accepted Answer

An exothermic reaction releases heat into the surroundings, which means that the products have less energy than the reactants. This typically leads to a negative ΔG (Gibbs free energy) value, making the reaction spontaneous at all temperatures. Therefore, the correct answer is A.

Question 5

Consider the reaction of 25.0 mL of 0.20 M AgNO₃(aq)with 25.0 mL of 0.20 M NaBr(aq)to form AgBr(s)at 25 °C.What is ΔG for this reaction? The K_sp of AgBr is 5.0 × 10^-13 at 25 °C. A)-58.8 kJ/mol B)-70.2 kJ/mol C)+58.8 kJ/mol D)+70.2 kJ/mol E)-28.3 kJ/mol

Accepted Answer

The equation for the reaction is:

AgNO3(aq) + NaBr(aq) → AgBr(s) + NaNO3(aq)

The reaction quotient Qc can be calculated as follows:

Qc = [AgBr]/([AgNO3]*[NaBr])

Substituting the given values:

Qc = [AgBr]/(0.20*0.025)^2

Qc = [AgBr]/1.25×10^-6

At equilibrium, Qc = Ksp, therefore:

Ksp = [AgBr]/1.25×10^-6

[AgBr] = Ksp * 1.25×10^-6

[AgBr] = 5.0×10^-13 * 1.25×10^-6

[AgBr] = 6.25×10^-19

The change in Gibbs free energy can be calculated using the formula:

ΔG = -RTlnK

Substituting the given values:

ΔG = -(8.314 J/mol*K) * (298 K) * ln(6.25×10^-19)

ΔG = -58.8 kJ/mol

Therefore, the correct answer is A) -58.8 kJ/mol.

Question 6

The equilibrium constant for the reaction below is 7.2 × 10^-4 at 298 K and 1 atm. HNO₂(aq)+ H₂O(l)⇌ NO₂^-(aq)+ H₃O⁺(aq) Which of the below statements is TRUE under the following conditions: [HNO₂(aq)] = 1.0 M and [NO₂^-(aq)] = [H₃O⁺(aq)] = 1.0 × 10^-5M A)the reaction is at equilibrium B)the forward reaction is spontaneous C)the reverse reaction is spontaneous D)the forward reaction is endothermic E)the reverse reaction is exothermic

Accepted Answer

The answer of The equilibrium constant for the reaction below...

Question 7

The following reaction is endothermic. 2 NH₃(g)→ N₂(g)+ 3 H₂(g) This means the reaction: A)will be spontaneous at high temperature B)will be spontaneous at low temperature C)is not spontaneous at any temperature D)is spontaneous at all temperatures E)cannot determine without temperature

Accepted Answer

For an endothermic reaction, increasing the temperature shifts the equilibrium to the right according to Le Chatelier's principle, making the reaction more likely to be spontaneous at high temperatures.

Question 8

Which of the following combinations of signs for △H and △S will always result in a reaction being non spontaneous? A)ΔH+,ΔS- B)ΔH-,ΔS+ C)ΔH-,ΔS- D)ΔH+,ΔS+ E)cannot determine without temperature

Accepted Answer

A reaction is non-spontaneous when ΔG is positive. According to the Gibbs free energy equation ΔG = ΔH - TΔS, if ΔH is positive and ΔS is negative, ΔG will always be positive regardless of the temperature, making the reaction non-spontaneous.

Question 9

For Cl₂O(g)+ 3/2 O₂(g)→ 2 ClO₂ △_rH° = 126 kJ/mol,and Δ_rS° = -74.9 J/(mol K)at 377 °C.What is K_eq? A)0.97 B)6.12 × 10^-7 C)4.27 × 10^-22 D)9.17 × 10^-15 E)1.07 × 10¹⁴

Accepted Answer

Using the equation ΔG1U1B1r= ΔH1U1B1r−TΔS1U1B1r, where T is the temperature in Kelvin, we can calculate ΔG1U1B1r as:
ΔG1U1B1r= (126,000 J/mol) - (377 K)(-74.9 J/(mol K))
ΔG1U1B1r= 151,923 J/mol

Then, we can use the equation ΔG1U1B1r= -RTlnK to solve for K:
-151,923 J/mol = -(8.314 J/(mol K))(377 K)lnK
lnK = -21.51
K = e^(-21.51) = 9.17 × 10^-15

Therefore, the answer is D, 9.17 × 10^-15.

Question 10

For an exothermic reaction to be non spontaneous at high temperatures,the enthalpy must be ________ while the entropy is ________.
A)positive,also positive
B)positive,negative
C)a relatively small negative value,also negative
D)a relatively large negative value,positive
E)a very large negative value,also negative

Accepted Answer

For an exothermic reaction to be non-spontaneous at high temperatures, the enthalpy change must be negative (indicating it releases heat), and the entropy change must also be negative (indicating a decrease in disorder). This combination can lead to a situation where, at high temperatures, the TΔS term in the Gibbs free energy equation (ΔG = ΔH - TΔS) becomes large enough to make ΔG positive, thus making the reaction non-spontaneous.

Question 11

Choose the INCORRECT statement about coupled reactions.
A)The usual practice of coupling reactions is to join two nonspontaneous reactions.
B)The usual reason to couple reactions is to produce an overall spontaneous reaction.
C)The reaction added to a nonspontaneous reaction needs to be spontaneous.
D)The reaction added to a nonspontaneous reaction needs to be more spontaneous than the original reaction is nonspontaneous.
E)One of the coupled reactions has a negative ΔG,the other a positive ΔG.

Accepted Answer

The statement "The usual practice of coupling reactions is to join two nonspontaneous reactions" is incorrect because the usual practice is to join a nonspontaneous reaction with a spontaneous one to produce an overall spontaneous reaction.

Question 12

Consider the reaction: N₂(g)+ 3 X₂(g)→ 2 NX₃(g) △_fH° (kJ/mol)0.0 0.0 43 S° (J/(mol K))192 210 172 What is K_eq for this reaction at 591 K? A)2.3 × 10¹⁷ B)4.3 × 10^-18 C)1.04 D)0.96 E)132

Accepted Answer

The equilibrium constant K_eq can be calculated using the Gibbs free energy change (ΔG°) and the relation ΔG° = -RT ln(K_eq). First, calculate ΔG° using ΔG° = ΔH° - TΔS°, where ΔH° and ΔS° are derived from the given formation enthalpies and entropies. The calculated ΔG° is positive, indicating a non-spontaneous reaction, leading to a very small K_eq value.

Question 13

Which of the following quantities for an element has a value of zero in the standard state? I.D_fH° II.D_fG° III.S° A)I only B)II only C)III only D)I and II E)I,II,and III

Accepted Answer

In the standard state, the standard enthalpy of formation (ΔfH°) and the standard Gibbs free energy of formation (ΔfG°) for an element in its most stable form are both zero. However, the standard entropy (S°) is not zero for an element in its standard state.

Question 14

If ΔG is positive for a certain reaction,then:
A)the reaction is spontaneous
B)the reverse of the reaction is spontaneous
C)the system is in equilibrium
D)one would need to know the Kelvin temperature to determine spontaneity
E)there would be no reaction possible for a negative value

Accepted Answer

If ΔG is positive, it means that the reaction is non-spontaneous in the forward direction. However, the reverse of the reaction would have a negative ΔG value, making it spontaneous. Therefore, the best choice is B, which states that the reverse of the reaction is spontaneous.

Question 15

For the reaction: CO(g)+ 2 H₂(g)→ CH₃OH(g) K_p = 91.4 at 350 K and K_p = 2.05 × 10^-4 at 298 K. What is the value of Δ_rH°? A)49.9 kJ/mol B)2.08 × 10³ kJ/mol C)3.74 × 10^-2 kJ/mol D)217 kJ/mol E)446 kJ/mol

Accepted Answer

From the given equilibrium constant values, we can calculate ΔG° at 298 K as follows:
ΔG° = -RTlnKp
ΔG° = -8.314 J/mol·K × (ln2.05 × 10^-4) = 217 kJ/mol
To calculate ΔS°, we need to use the equation:
ΔG° = ΔH° - TΔS°
ΔS° = (ΔH° - ΔG°)/T
Since we do not have the value of ΔH°, we cannot calculate ΔS° directly. However, we know that ΔS° is positive if the reaction produces more gas molecules than it consumes, and negative if the reaction consumes more gas molecules than it produces. In this case, we can see that the reaction consumes one molecule of CO and two molecules of H2S, but produces one molecule of CH3OH. Therefore, we expect ΔS° to be negative. Among the answer choices, only D is negative, so D is the correct answer.

Question 16

For the reaction PCl₅ (g)⇌ PCl₃ (g)+ Cl₂ (g),K_c = 0.0454 at 261 °C.If a vessel is filled with theses gases such that the initial concentrations are [PCl₅] = 0.2 M,[PCl₃] = 0.2 M,and [Cl₂] = 2.25 M,the value of the reaction quotient is: A)Q_c= 1.8 B)Q_c= 0.56 C)Q_c= 2.8 D)Q_c= 0.0454 E)Q_c= 1

Accepted Answer

The reaction quotient $Q_c$ is calculated using the initial concentrations of the products raised to their stoichiometric coefficients divided by the initial concentrations of the reactants raised to their stoichiometric coefficients. For the given reaction, $Q_c = \frac{[PCl_3][Cl_2]}{[PCl_5]}$. Substituting the given concentrations, $Q_c = \frac{(0.2)(2.25)}{0.2} = 2.25$. However, due to a mistake in the calculation, the correct process was described but the final answer was incorrectly stated as 1.8 instead of the correct calculation result, which should be 2.25 based on the provided explanation.

Question 17

If the vapor pressure of water in an open system at 25 °C is 23.8 mmHg,what is Δ_rG for the reaction below at 25 °C? H₂O(l)→ H₂O(g,23.8 mmHg) A)0 kJ/mol B)-8.58 kJ/mol C)+8.58 kJ/mol D)-0.720 kJ/mol E)+0.720 kJ/mol

Accepted Answer

The correct answer is A because the vapor pressure of water in an open system at 25 °C is 23.8 mmHg, which is equal to the equilibrium vapor pressure of water at 25 °C. Therefore, the change in free energy for the reaction is zero.

Question 18

Which of the following quantities is practically independent of temperature?
I.ΔH
II.ΔS
III.ΔG
A)I only
B)II only
C)III only
D)I and II
E)I,II,and III

Accepted Answer

ΔH (enthalpy change) and ΔS (entropy change) are generally considered to be relatively independent of temperature over small temperature ranges, while ΔG (Gibbs free energy change) is temperature-dependent as it is calculated using the equation ΔG = ΔH - TΔS.

Question 19

Choose the INCORRECT statement. A)The van't Hoff equation is ln B)K_eq is independent of temperature. C)In a thermodynamic equilibrium constant expression,the activity of a gas is replaced by its partial pressure in atmosphere. D)In a K_eq expression,the activity of an aqueous species can be approximated by the numerical value of its molarity. E)If ΔG = 0,the process is at equilibrium.

Accepted Answer

The answer of Choose the INCORRECT statement.
A)The van't Hoff equation...

Question 20

For the reaction PCl₅ (g)⇌ PCl₃ (g)+ Cl₂ (g),K_c = 0.0454 at 261 °C.If a vessel is filled with theses gases such that the initial concentrations are [PCl₅] = 0.2 M,[PCl₃] = 0.2 M,and [Cl₂] = 2.25 M,which of the following statements is TRUE? A)the reaction is at equilibrium B)the forward reaction is spontaneous C)the reverse reaction is spontaneous D)the forward reaction is exothermic E)the reverse reaction is exothermic

Accepted Answer

We can examine the reaction quotient Qc to determine whether the reaction has reached equilibrium or not. Using the initial concentrations given, we can calculate Qc:

Qc = [PCl3][Cl2] / [PCl5] 
= (0.2 M)(2.25 M) / (0.2 M)^2 
= 2.25

Since Qc is greater than the equilibrium constant Kc, the reaction will shift towards the products to reach equilibrium. Therefore, the reverse reaction is spontaneous (choice C) while the forward reaction is not spontaneous. We cannot determine whether the forward reaction is exothermic or endothermic from the information given.

Quiz 13: Spontaneous Change: Entropy and Gibbs Energy

For the reaction PCl₅(g) → PCl₃(g) + Cl₂(g) at 298 K,K_eq = 1.87 × 10^-7,what is Δ_rG ° and is the reaction spontaneous?

A reaction is spontaneous if: I.ΔG is a negative value II.both enthalpy and entropy increase III.ΔH is negative and ΔS is positive IV.both enthalpy and entropy decrease V.ΔH is positive and ΔS is negative

The equilibrium constant for the reaction below is 7.2 × 10^-4 at 298 K and 1 atm. HNO₂(aq) + H₂O(l) ⇌ NO₂^-(aq) + H₃O⁺(aq) When [HNO₂(aq) ] = 1.0 M and [NO₂^-(aq) ] = [H₃O⁺(aq) ] = 1.0 × 10^-5M,calculate ΔG.

The following reaction is exothermic. 2 N₂O(g) → 2 N₂(g) + O₂(g) This means the reaction:

Consider the reaction of 25.0 mL of 0.20 M AgNO₃(aq) with 25.0 mL of 0.20 M NaBr(aq) to form AgBr(s) at 25 °C.What is ΔG for this reaction? The K_sp of AgBr is 5.0 × 10^-13 at 25 °C.

The equilibrium constant for the reaction below is 7.2 × 10^-4 at 298 K and 1 atm. HNO₂(aq) + H₂O(l) ⇌ NO₂^-(aq) + H₃O⁺(aq) Which of the below statements is TRUE under the following conditions: [HNO₂(aq) ] = 1.0 M and [NO₂^-(aq) ] = [H₃O⁺(aq) ] = 1.0 × 10^-5M

The following reaction is endothermic. 2 NH₃(g) → N₂(g) + 3 H₂(g) This means the reaction:

Which of the following combinations of signs for △H and △S will always result in a reaction being non spontaneous?

For Cl₂O(g) + 3/2 O₂(g) → 2 ClO₂ △_rH° = 126 kJ/mol,and Δ_rS° = -74.9 J/(mol K) at 377 °C.What is K_eq?

For an exothermic reaction to be non spontaneous at high temperatures,the enthalpy must be while the entropy is .

Choose the INCORRECT statement about coupled reactions.

Consider the reaction: N₂(g) + 3 X₂(g) → 2 NX₃(g) △_fH° (kJ/mol) 0.0 0.0 43 S° (J/(mol K) ) 192 210 172 What is K_eq for this reaction at 591 K?

Which of the following quantities for an element has a value of zero in the standard state? I.D_fH° II.D_fG° III.S°

If ΔG is positive for a certain reaction,then:

For the reaction: CO(g) + 2 H₂(g) → CH₃OH(g) K_p = 91.4 at 350 K and K_p = 2.05 × 10^-4 at 298 K. What is the value of Δ_rH°?

For the reaction PCl₅ (g) ⇌ PCl₃ (g) + Cl₂ (g) ,K_c = 0.0454 at 261 °C.If a vessel is filled with theses gases such that the initial concentrations are [PCl₅] = 0.2 M,[PCl₃] = 0.2 M,and [Cl₂] = 2.25 M,the value of the reaction quotient is:

If the vapor pressure of water in an open system at 25 °C is 23.8 mmHg,what is Δ_rG for the reaction below at 25 °C? H₂O(l) → H₂O(g,23.8 mmHg)

Which of the following quantities is practically independent of temperature? I.ΔH II.ΔS III.ΔG

Choose the INCORRECT statement.

For the reaction PCl₅ (g) ⇌ PCl₃ (g) + Cl₂ (g) ,K_c = 0.0454 at 261 °C.If a vessel is filled with theses gases such that the initial concentrations are [PCl₅] = 0.2 M,[PCl₃] = 0.2 M,and [Cl₂] = 2.25 M,which of the following statements is TRUE?

Quiz 13: Spontaneous Change: Entropy and Gibbs Energy

For the reaction PCl5(g) → PCl3(g) + Cl2(g) at 298 K,Keq = 1.87 × 10-7,what is ΔrG ° and is the reaction spontaneous?

A reaction is spontaneous if: I.ΔG is a negative value II.both enthalpy and entropy increase III.ΔH is negative and ΔS is positive IV.both enthalpy and entropy decrease V.ΔH is positive and ΔS is negative

The equilibrium constant for the reaction below is 7.2 × 10-4 at 298 K and 1 atm. HNO2(aq) + H2O(l) ⇌ NO2-(aq) + H3O+(aq) When [HNO2(aq) ] = 1.0 M and [NO2-(aq) ] = [H3O+(aq) ] = 1.0 × 10-5 M,calculate ΔG.

The following reaction is exothermic. 2 N2O(g) → 2 N2(g) + O2(g) This means the reaction:

Consider the reaction of 25.0 mL of 0.20 M AgNO3(aq) with 25.0 mL of 0.20 M NaBr(aq) to form AgBr(s) at 25 °C.What is ΔG for this reaction? The Ksp of AgBr is 5.0 × 10-13 at 25 °C.

The equilibrium constant for the reaction below is 7.2 × 10-4 at 298 K and 1 atm. HNO2(aq) + H2O(l) ⇌ NO2-(aq) + H3O+(aq) Which of the below statements is TRUE under the following conditions: [HNO2(aq) ] = 1.0 M and [NO2-(aq) ] = [H3O+(aq) ] = 1.0 × 10-5 M

The following reaction is endothermic. 2 NH3(g) → N2(g) + 3 H2(g) This means the reaction: