Question 1

A 100 mL sample of water is placed in a coffee cup calorimeter.When 1.0 g of an ionic solid is added,the temperature decreases from 21.5 °C to 20.8 °C as the solid dissolves.For the dissolving of the solid,_____. A) ΔH < 0 B) ΔS(universe)> 0 C) ΔS(system)< 0 D) ΔS(surroundings)> 0 E) None of these

Accepted Answer

The answer of A 100 mL sample of water is...

Question 2

While diluting concentrated sulfuric acid with water,the temperature of the solution increases rapidly.What are the signs of ΔrH,ΔrS,and ΔrG for the process? A) Δ_rH < 0,Δ_rS > 0,and Δ_rG < 0 B) Δ_rH < 0,Δ_rS < 0,and Δ_rG < 0 C) Δ_rH < 0,Δ_rS > 0,and Δ_rG > 0 D) Δ_rH > 0,Δ_rS > 0,and Δ_rG < 0 E) Δ_rH > 0,Δ_rS < 0,and Δ_rG > 0

Accepted Answer

The process is exothermic (ΔrH < 0) because heat is released. The entropy of the system increases (ΔrS > 0) because the sulfuric acid molecules become more dispersed in the water. The Gibbs free energy of the system decreases (ΔrG < 0) because the process is spontaneous.

Question 3

For the reaction given below,ΔH⁰ = −1516 kJ at 25°C and ΔS⁰ = −432.8 J/K at 25°C.This reaction is spontaneous _____. SiH₄(g)+ 2 O₂(g)→ SiO₂(s)+ 2 H₂O A) only below a certain temperature B) only above a certain temperature C) at all temperatures D) only when entropy is zero E) None of these

Accepted Answer

The answer of For the reaction given below,ΔH⁰ = −1516...

Question 4

At what temperatures will a reaction be spontaneous if Δ_rH° = +117 kJ and Δ_rS° = -35 J/K? A) All temperatures below 94.1 K B) Temperatures between 12.7 K and 135 K C) All temperatures above 94.1 K D) The reaction will be spontaneous at any temperature. E) The reaction will never be spontaneous.

Accepted Answer

A reaction is spontaneous when ΔG° < 0. Since ΔrH° is positive and ΔrS° is negative, ΔG° = ΔrH° - TΔrS° will always be positive, making the reaction non-spontaneous at any temperature.

Question 5

If Δ_rG° > 0 for a reaction at all temperatures,then Δ_rH° is _____ and Δ_rS° is _____. A) Negative; positive B) Positive; negative C) Negative; negative D) Positive; positive E) Positive; either positive or negative

Accepted Answer

If Δ_rG° > 0, then the reaction is spontaneous and Δ_rH° is positive, indicating that energy is absorbed by the reaction. This means that the products are less stable than the reactants. Furthermore, Δ_rS° is negative, indicating that the reaction leads to a decrease in disorder or an increase in order. The correct answer is therefore B, which has a positive Δ_rH° and a negative Δ_rS°.

Question 6

Calculate ΔG° at 298 K for the reaction below. I₂(g)+ Br₂(g)→ 2IBr(g) Given: Δ_rH° = -11.6 kJ/mol-rxn; Δ_rS° = 12 J/K⋅mol-rxn at 298 K. A) -8.02 kJ/mol-rxn B) 15.2 kJ/mol-rxn C) -15.2 kJ/mol-rxn D) 3.59 × 10³ kJ/mol-rxn E) -3.59 × 10³ kJ/mol-rxn

Accepted Answer

ΔG° = ΔH° - TΔS°

ΔS° is given as 12 J/K⋅mol-rxn, which needs to be converted to kJ/K⋅mol-rxn.
ΔS° = 12 J/K⋅mol-rxn × (1 kJ/1000 J) = 0.012 kJ/K⋅mol-rxn

Substituting the values given:
ΔG° = (-11.6 kJ/mol-rxn) - (298 K)(0.012 kJ/K⋅mol-rxn) = -15.2 kJ/mol-rxn

Therefore, the answer is C, -15.2 kJ/mol-rxn.

Question 7

A change of state occurring in a system is accompanied by 60.7 kJ of heat that is transferred to the surroundings at a constant pressure and at a constant temperature of 300 K.Calculate the ΔS(surroundings)for the process.
A) -202 J/K
B) -60.7 kJ/K
C) 202 J/K
D) 60.7 kJ/K
E) 239 kJ/K

Accepted Answer

The answer of A change of state occurring in a...

Question 8

If a chemical reaction is exothermic but not spontaneous,which of the following must be true? A) Δ_rG > 0,Δ_rS > 0,and Δ_rH > 0 B) Δ_rG < 0,Δ_rS > 0,and Δ_rH > 0 C) Δ_rG > 0,Δ_rS < 0,and Δ_rH > 0 D) Δ_rG < 0,Δ_rS < 0,and Δ_rH < 0 E) Δ_rG > 0,Δ_rS < 0,and Δ_rH < 0

Accepted Answer

An exothermic reaction has Δ_rH < 0. If it is not spontaneous, Δ_rG > 0. For Δ_rG to be positive, Δ_rS must be negative when Δ_rH is negative.

Question 9

At what temperatures will a reaction be spontaneous if Δ_rH° = +62.4 kJ and Δ_rS° = +301 J/K? A) All temperatures below 207 K B) All temperatures above 207 K C) Temperatures between 179 K and 235 K D) The reaction will be spontaneous at any temperature E) The reaction will never be spontaneous

Accepted Answer

To determine the temperature range for spontaneity, we use the Gibbs free energy equation: ΔG = ΔH - TΔS. A reaction is spontaneous when ΔG < 0. Given ΔH° = +62.4 kJ = 62400 J (since 1 kJ = 1000 J) and ΔS° = +301 J/K, we find the temperature at which ΔG = 0 to determine the boundary of spontaneity. Setting ΔG = 0 gives 0 = ΔH - TΔS, or T = ΔH/ΔS. Plugging in the values, T = 62400 J / 301 J/K = 207.31 K. Since ΔH is positive and ΔS is positive, the reaction becomes more spontaneous at higher temperatures. Therefore, the reaction is spontaneous at temperatures above 207 K.

Question 10

Calculate Δ_rG° at 25.0 °C for the reaction below. 2 Na(s)+ 2 H₂O( )→ 2 NaOH(aq)+ H₂(g) Given: Δ_rH° = −366.6 kJ/mol-rxn and Δ_rS° = −154.2 J/K⋅mol-rxn. A) -371.2 kJ/mol-rxn B) -320.6 kJ/mol-rxn C) -215.4 kJ/mol-rxn D) +371.2 kJ/mol-rxn E) +4634.9 kJ/mol-rxn

Accepted Answer

The answer of Calculate Δ_rG° at 25.0 °C for the...

Question 11

ΔG° = 0 for a reaction indicates that _____.
A) the reaction favors formation of products
B) the reaction is at equilibrium
C) the reaction is nonspontaneous
D) the reaction is spontaneous
E) the reaction cannot reach equilibrium

Accepted Answer

When ΔG° = 0, it means that the free energy change of the reaction under standard conditions is zero. This only happens at equilibrium, when the rates of the forward and reverse reactions are equal and there is no net change in the concentrations of the reactants and products.

Question 12

A flask containing helium gas is released into a closed room.Which of the following ideas concerning entropy is/are true?
A) ΔS(system)> 0
B) Matter is dispersed.
C) ΔS(universe)> 0
D) This process is spontaneous.
E) All of these statements are true.

Accepted Answer

A) ΔS(system)> 0: As the gas expands into the room, the number of microstates available to the gas molecules increases, leading to an increase in entropy. Therefore ΔS(system)> 0.
B) Matter is dispersed: Since the gas in the flask is released into the room, it spreads out, making matter more dispersed.
C) ΔS(universe)> 0: The entropy change of the system and its surroundings is always positive for an irreversible process. In this case, the system is the helium gas and the surroundings are the rest of the room. Therefore, ΔS(universe)> 0.
D) This process is spontaneous: This process occurs spontaneously without any external intervention, so it is spontaneous.
Therefore, all of these statements are true.

Question 13

If a cube of ice at 0 °C is placed outside on a warm summer day,the ice will melt spontaneously.What are the signs of Δ_rH,Δ_rS,and Δ_rG for the process? A) Δ_rH < 0,Δ_rS > 0,and Δ_rG < 0 B) Δ_rH < 0,Δ_rS < 0,and Δ_rG < 0 C) Δ_rH < 0,Δ_rS > 0,and Δ_rG > 0 D) Δ_rH > 0,Δ_rS > 0,and Δ_rG < 0 E) Δ_rH > 0,Δ_rS < 0,and Δ_rG > 0

Accepted Answer

The melting of ice into water is an endothermic process (absorbs heat) so ΔH > 0. The disorder increases as solid ice turns into liquid water, so ΔS > 0. For a process to be spontaneous at constant temperature and pressure, ΔG must be < 0.

Question 14

For a reaction,Δ_rH° = -208.8 kJ and Δ_rS° = -308.2 J/K.At what temperature will Δ_rG° = 0.00 kJ? A) 0.68 K B) 677.5 K C) 1476 K D) 6435 K E) 0.85 K

Accepted Answer

We know that:
ΔG° = ΔH° - TΔS°
At equilibrium, ΔG° = 0
Therefore:
0 = -208.8 kJ - T(-308.2 J/K)
0 = -208.8 kJ + 0.3082 kJ K⁻¹ T
T = (208.8 kJ)/(0.3082 kJ K⁻¹) = 677.5 K

Therefore, the best choice is B.

Question 15

Hydrogen gas is prepared by electrolysis of water according to the reaction below. 2 H₂O( )→ 2 H₂(g)+ O₂(g) Predict the signs of Δ_rH and Δ_rS. A) Δ_rH > 0 and Δ_rS > 0 B) Δ_rH < 0 and Δ_rS > 0 C) Δ_rH > 0 and Δ_rS < 0 D) Δ_rH < 0 and Δ_rS < 0 E) Δ_rH = 0 and Δ_rS < 0

Accepted Answer

The answer of Hydrogen gas is prepared by electrolysis of...

Question 16

For a chemical reaction,if Δ_rG° = 0,then _____. A) K > 0 B) K = 0 C) K < 0 D) K > 1 E) K = 1

Accepted Answer

Δ_rG° = ΔS° - R ln(K) When Δ_rG° = 0, ΔS° - R ln(K) = 0 So, ΔS° = R ln(K) For K = 1, the ln(K) becomes 0, and 0 multiplied by any value is 0. Thus, ΔS° = R ln(K) = 0. Therefore, the answer is K = 1.

Question 17

Which of the following is correct for the condensation of gaseous oxygen at -188 °C? (The normal boiling point of oxygen is -183 °C.) A) ΔH < 0,ΔS > 0,and ΔG > 0. B) ΔH < 0,ΔS < 0,and ΔG >0. C) ΔH > 0,ΔS < 0,and ΔG < 0. D) ΔH = 0,ΔS = 0,and ΔG < 0. E) ΔH > 0,ΔS > 0,and ΔG > 0.

Accepted Answer

Condensation is an exothermic process (releases heat), so ΔH < 0. It involves a gas becoming a liquid, which decreases the system's entropy (ΔS < 0). Since the process is spontaneous at -188 °C (below the boiling point), ΔG must be < 0, not > 0. Therefore, the correct statement should indicate ΔH < 0, ΔS < 0, and ΔG < 0, but none of the options correctly states ΔG < 0 for a spontaneous process. Given the options, B is the closest to being correct, acknowledging an error in the explanation regarding ΔG's sign based on the provided choices.

Question 18

Which of the following is true of a reaction that is product-favored? A) Q < K and _rG < 0 B) Q < K and _rG > 0 C) Q = K and _rG = 0 D) Q > K and _rG < 0 E) Q > K and _rG > 0

Accepted Answer

The answer of Which of the following is true of...

Question 19

When a real gas is compressed from low pressure to high pressure,its temperature increases.Which of the following is true for ΔH and ΔS? A) ΔH < 0 and ΔS < 0 B) ΔH < 0 and ΔS > 0 C) ΔH > 0 and ΔS < 0 D) ΔH > 0 and ΔS > 0 E) ΔH < 0 and ΔS = 0

Accepted Answer

The answer of When a real gas is compressed from...

Question 20

The dissolution of ammonium nitrate occurs spontaneously in water at 25 °C.As ammonium nitrate dissolves,the temperature of the water decreases.What are the signs of Δ_rH,Δ_rS,and Δ_rG for this process? A) Δ_rH > 0,Δ_rS < 0,and Δ_rG > 0 B) Δ_rH > 0,Δ_rS > 0,and Δ_rG > 0 C) Δ_rH > 0,Δ_rS > 0,and Δ_rG < 0 D) Δ_rH < 0,Δ_rS < 0,and Δ_rG < 0 E) Δ_rH < 0,Δ_rS > 0,and Δ_rG > 0

Accepted Answer

The dissolution of ammonium nitrate in water is an exothermic process (it releases heat), so Δ_rH is expected to be positive. As the temperature of the water decreases during the process, this implies that the entropy of the system (ammonium nitrate and water) decreases as well, hence Δ_rS should also be positive. Finally, since the reaction is spontaneous (it occurs without the need of external work), it follows that the Gibbs free energy of the system (Δ_rG) is negative. Therefore, the best choice is C, with Δ_rH > 0, Δ_rS > 0, and Δ_rG < 0.

Quiz 19: Principles of Chemical Reactivity: Entropy and Free Energy

A 100 mL sample of water is placed in a coffee cup calorimeter.When 1.0 g of an ionic solid is added,the temperature decreases from 21.5 °C to 20.8 °C as the solid dissolves.For the dissolving of the solid,_____.

While diluting concentrated sulfuric acid with water,the temperature of the solution increases rapidly.What are the signs of ΔrH,ΔrS,and ΔrG for the process?

For the reaction given below,ΔH⁰ = −1516 kJ at 25°C and ΔS⁰ = −432.8 J/K at 25°C.This reaction is spontaneous _____. SiH₄(g) + 2 O₂(g) → SiO₂(s) + 2 H₂O

At what temperatures will a reaction be spontaneous if Δ_rH° = +117 kJ and Δ_rS° = -35 J/K?

If Δ_rG° > 0 for a reaction at all temperatures,then Δ_rH° is _____ and Δ_rS° is _____.

Calculate ΔG° at 298 K for the reaction below. I₂(g) + Br₂(g) → 2IBr(g) Given: Δ_rH° = -11.6 kJ/mol-rxn; Δ_rS° = 12 J/K⋅mol-rxn at 298 K.

A change of state occurring in a system is accompanied by 60.7 kJ of heat that is transferred to the surroundings at a constant pressure and at a constant temperature of 300 K.Calculate the ΔS(surroundings) for the process.

If a chemical reaction is exothermic but not spontaneous,which of the following must be true?

At what temperatures will a reaction be spontaneous if Δ_rH° = +62.4 kJ and Δ_rS° = +301 J/K?

Calculate Δ_rG° at 25.0 °C for the reaction below. 2 Na(s) + 2 H₂O( ) → 2 NaOH(aq) + H₂(g) Given: Δ_rH° = −366.6 kJ/mol-rxn and Δ_rS° = −154.2 J/K⋅mol-rxn.

ΔG° = 0 for a reaction indicates that _____.

A flask containing helium gas is released into a closed room.Which of the following ideas concerning entropy is/are true?

If a cube of ice at 0 °C is placed outside on a warm summer day,the ice will melt spontaneously.What are the signs of Δ_rH,Δ_rS,and Δ_rG for the process?

For a reaction,Δ_rH° = -208.8 kJ and Δ_rS° = -308.2 J/K.At what temperature will Δ_rG° = 0.00 kJ?

Hydrogen gas is prepared by electrolysis of water according to the reaction below. 2 H₂O( ) → 2 H₂(g) + O₂(g) Predict the signs of Δ_rH and Δ_rS.

For a chemical reaction,if Δ_rG° = 0,then _____.

Which of the following is correct for the condensation of gaseous oxygen at -188 °C? (The normal boiling point of oxygen is -183 °C.)

Which of the following is true of a reaction that is product-favored?

When a real gas is compressed from low pressure to high pressure,its temperature increases.Which of the following is true for ΔH and ΔS?

The dissolution of ammonium nitrate occurs spontaneously in water at 25 °C.As ammonium nitrate dissolves,the temperature of the water decreases.What are the signs of Δ_rH,Δ_rS,and Δ_rG for this process?

Quiz 19: Principles of Chemical Reactivity: Entropy and Free Energy

A 100 mL sample of water is placed in a coffee cup calorimeter.When 1.0 g of an ionic solid is added,the temperature decreases from 21.5 °C to 20.8 °C as the solid dissolves.For the dissolving of the solid,_____.

While diluting concentrated sulfuric acid with water,the temperature of the solution increases rapidly.What are the signs of ΔrH,ΔrS,and ΔrG for the process?

For the reaction given below,ΔH0 = −1516 kJ at 25°C and ΔS0 = −432.8 J/K at 25°C.This reaction is spontaneous _____. SiH4(g) + 2 O2(g) → SiO2(s) + 2 H2O

At what temperatures will a reaction be spontaneous if ΔrH° = +117 kJ and ΔrS° = -35 J/K?

If ΔrG° > 0 for a reaction at all temperatures,then ΔrH° is _____ and ΔrS° is _____.

Calculate ΔG° at 298 K for the reaction below. I2(g) + Br2(g) → 2IBr(g) Given: ΔrH° = -11.6 kJ/mol-rxn; ΔrS° = 12 J/K⋅mol-rxn at 298 K.