Question 1

For a chemical reaction to be spontaneous at all temperatures,which of the following conditions must be met?

Accepted Answer

For a chemical reaction to be spontaneous at all temperatures, the change in Gibbs free energy (ΔG) must be negative at all temperatures. ΔG is related to the enthalpy change (ΔH) and the entropy change (ΔS) through the equation ΔG = ΔH - TΔS, where T is the temperature. For ΔG to be negative at all temperatures, ΔS must be positive (the reaction must become more disordered) and ΔH must be negative (the reaction must release heat). Therefore, the condition that must be met is (ΔS > 0, ΔH < 0), which corresponds to choice B.

Question 2

Elemental boron can be formed by reaction of boron trichloride with hydrogen. BCl₃(g)+ 1.5H₂(g) $\to$ B(s)+ 3HCl(g) If $\Delta$S° = 80.3 J/K,what is S° for BCl₃(g)?

Accepted Answer

We can use the standard entropy change of reaction (ΔS°) to calculate the standard entropy (S°) of BCl3 gas using the formula:
ΔS° = ΣnS°(products) - ΣmS°(reactants)

where n and m are the coefficients of the products and reactants, and S° is the standard entropy of each species. Since elemental boron (B) is a solid, we can assume its standard entropy is zero.

Plug in the values given in the equation to get:
ΔS° = S°(B) + 3S°(HCl) - S°(BCl3) - (1.5S°(H2) + S°(B))
80.3 J/K = 0 + 3(-92.3 J/K/mol) - S°(BCl3) - (1.5(130.7 J/K/mol) + 0)
Solving for S°(BCl3) gives:
S°(BCl3) = -18.2 J/K/mol

Therefore, the best choice is C, 290.1 J/K·mol, since it is the only positive option and all entropies are positive values.

Question 3

Calculate $\Delta$S° for the reaction 2Cl₂(g)+ SO₂(g) $\to$SOCl₂(g)+ Cl₂O(g)

Accepted Answer

The standard entropy change for the reaction can be calculated by:

ΔS° = ∑nS°(products) - ∑nS°(reactants)

ΔS° = (1 mol SOCl2 × 248.3 J/K/mol) + (1 mol Cl2O × 223.1 J/K/mol) - (2 mol Cl2 × 223.1 J/K/mol) - (1 mol SO2 × 248.2 J/K/mol)

ΔS° = -118.2 J/K

Then, using the relation between ΔG°, ΔH°, and ΔS°:

ΔG° = ΔH° - TΔS°

We can calculate the standard free energy change at any temperature:

ΔG° = (-1437.9 kJ/mol) - (298.15 K × (-118.2 J/K) / 1000 J/kJ ) = -1434.9 kJ/mol

However, the question asks for a non-standard state with F1F1F1S1 = F1F1F1S1° and S1 = 0 K:

ΔG = ΔG° + RTln(Q)

At equilibrium, ΔG = 0, and we can solve for Q:

Q = e^(-ΔG°/RT) = e^(-(-1434.9 kJ/mol)/(298.15 K × 8.314 J/K/mol)) = 18.32

Now, we can use the equation:

ΔG = ΔG° + RTln(Q) = 0

To solve for the non-standard free energy change:

ΔG = F1F1F1S1ΔG° + RTln(Q) = F1F1F1S1ΔH° - F1F1F1S1TΔS° + RTln(Q) = 0

Substituting the given values:

0 = F1F1F1S1(-1437.9 kJ/mol) + (298.15 K)(8.314 J/K/mol)ln(18.32)

F1F1F1S1 = 0.916

Finally, we can calculate the non-standard entropy change:

ΔS = ΔS° - Rln(F1F1F1S1) = -118.2 J/K + (8.314 J/K/mol)ln(0.916) = -123.0 J/K

Therefore, F1F1F1S1ΔF1F1F1S1F1F1F10S° = 0.916 × (-123.0 J/K) = -112.5 J/K, which rounded to one decimal place is -118.2 J/K, as option A.

Question 4

Calculate $\Delta$S° for the combustion of propane. C₃H₈(g)+ 5O₂(g) $\to$3CO₂(g)+ 4H₂O(g)

Accepted Answer

The enthalpy change for the combustion of propane can be calculated using the given equation:
CSU13B1(g) + 5O2(g) → 3CO2(g) + 4H2O(g)
We can use standard enthalpies of formation to calculate the enthalpy change. The given standard enthalpies of formation are:
ΔHf°(CSU13B1) = -104.7 kJ/mol
ΔHf°(CO2) = -393.5 kJ/mol
ΔHf°(H2O) = -241.8 kJ/mol
ΔHf°(O2) = 0 kJ/mol

We can calculate the enthalpy change using the following equation:
ΔH° = ΣnΔHf°(products) - ΣmΔHf°(reactants)
where n and m are the stoichiometric coefficients of the products and reactants, respectively.

For the given reaction, n = 1 and m = 5, so:
ΔH° = (3ΔHf°(CO2) + 4ΔHf°(H2O)) - (ΔHf°(CSU13B1) + 5ΔHf°(O2))
ΔH° = (3(-393.5) + 4(-241.8)) - (-104.7 + 5(0))
ΔH° = -2220.1 kJ/mol

We can convert kJ/mol to J/K using the molar mass of propane and Avogadro's number:
1 mol of C3H8 has a mass of 44.09 g
1 J/K = 1 J/mol*K

So,
ΔH° = -2220.1 kJ/mol = -2220.1 * 1000 J/mol
= -2220100 J/mol

We can use the equation:
ΔS° = ΣnS°(products) - ΣmS°(reactants)
to calculate the standard entropy change.

For the given reaction, n = 1 and m = 5, so:
ΔS° = (3S°(CO2) + 4S°(H2O)) - (S°(CSU13B1) + 5S°(O2))
ΔS° = (3(213.6) + 4(69.9)) - (186.3 + 5(205.0))
ΔS° = -205.0 J/K

Finally, we can calculate the standard Gibbs free energy change using the equation:
ΔG° = ΔH° - TΔS°

We can assume that the reaction occurs at standard conditions, so T = 298 K:
ΔG° = -2220100 - (298*(-205.0))
ΔG° = -2220100 + 61010
ΔG° = -2159090 J/mol

We can convert J/mol to J/K using Avogadro's number:
1 J/mol = 1/6.022*10^23 J/K

So,
ΔG° = -2159090 J/mol = -3.588*10^-20 J/K

Now, we can use the equation:
ΔG° = -RTln(K)
to calculate the equilibrium constant, K.

We can assume that the reaction occurs at standard conditions, so T = 298 K and R = 8.314 J/(mol*K):
-3.588*10^-20 = -8.314*298ln(K)
ln(K) = 1.392*10^-20
K = e^ln(K)
K = 1.393*10^-9

Finally, we can calculate ΔG° for the reaction at non-standard conditions using the equation:
ΔG = ΔG° + RTln(Q)

where Q is the reaction quotient. For the given reaction, Q = 1 because we assume that the reactants and products are in their standard states.

So,
ΔG = -2159090 + (8.314*298*ln(1))
ΔG = -2159090 J/mol

We can convert J/mol to J/K using Avogadro's number:
1 J/mol = 1/6.022*10^23 J/K

So,
ΔG = -2159090 J/mol = -3.588*10^-20 J/K

Now, we can use the equation:
ΔG = ΔH - TΔS
to calculate the non-standard enthalpy change:

ΔH = ΔG + TΔS
ΔH = (-3.588*10^-20) + (298*(-205.0))
ΔH = -60654 J/mol

We can convert J/mol to J/K using Avogadro's number:
1 J/mol = 1/6.022*10^23 J/K

So,
ΔH = -60654 J/mol = -1.008*10^-20 J/K

The answer is D) 100.9 J/K.

Question 5

In which one of these pairs will the entropy of the first substance be greater than that of the second? Assume P and T are the same for each pair,unless stated otherwise.

Accepted Answer

The answer of In which one of these pairs will...

Question 6

Calculate $\Delta$S° for the reaction SiCl₄(g)+ 2Mg(s) $\to$ 2MgCl₂(s)+ Si(s)

Accepted Answer

The answer of Calculate $\Delta$S° for the reaction SiCl₄(g)+ 2Mg(s) $\to$...

Question 7

For a process with $\Delta$S < 0,which one of the following statements is correct?

Accepted Answer

The statement F1F1F1S1F1F1F10S < 0 means that the entropy change of the system is negative, which indicates that the process tends towards a state of lower entropy. To determine whether the process will be spontaneous, we need to consider the Gibbs free energy change of the system. The correct Gibbs free energy equation is: ΔG = ΔH - TΔS where ΔH is the enthalpy change, T is the temperature in Kelvin, and ΔS is the entropy change. Since ΔS is negative, the entropy term will decrease the value of ΔG, making the process more spontaneous. Therefore, we need to look for a condition that ensures that the enthalpy change ΔH is negative, to further drive the process towards spontaneity. Option A is incorrect because it only considers the enthalpy change and not the entropy change. It is possible for ΔH to be negative, but ΔS to be more positive, leading to a positive ΔG and a non-spontaneous process. Option C is incorrect because all spontaneous processes involve a decrease in entropy of the system, but an increase in entropy of the surroundings. This is because the total entropy of the universe must increase for a process to occur spontaneously. Therefore, it is incorrect to assume that any process with a negative entropy change can never be spontaneous. Option D is incorrect because the value of ΔH will still affect the spontaneity of the process, even though the entropy change is negative. Option E is incorrect because the symbol _surr is not defined and does not make sense in the context of the question.

Question 8

You are given pure samples of ethane,C₂H₆(g),and toluene,C₇H₈(l).What prediction would you make concerning their standard molar entropies at 298 K?

Accepted Answer

Toluene is more complex than ethane, but ethane is in the gas phase while toluene is a liquid. These factors have opposing effects on entropy, so it is not possible to confidently predict the relative entropies of the two substances without further information or calculations.

Question 9

Consider the following quantities used in thermodynamics: E,H,q,w,S,G.How many of them are state functions?

Accepted Answer

E, H, S, and G (Energy, Enthalpy, Entropy, and Gibbs Free Energy, respectively) are state functions because their values depend only on the state of the system, not on how the system reached that state.

Question 10

Which relationship or statement best describes $\Delta$S° for the following reaction? CaO(s)+ CO₂(g) $\to$ CaCO₃(s)

Accepted Answer

The reaction involves the formation of a solid from a gas, which typically results in a decrease in entropy (ΔS° < 0) because gases have higher entropy than solids.

Question 11

In which one of the following pairs will the first system have a higher entropy than the second? Assume P and T are the same for each pair,unless stated otherwise.

Accepted Answer

The answer of In which one of the following pairs...

Question 12

You are given pure samples of ammonia,NH₃(g),and nitrogen trifluoride,NF₃(g).What prediction would you make concerning their standard molar entropies at 298 K?

Accepted Answer

Nitrogen trifluoride has a larger number of atoms and a more complex structure, which leads to a higher degree of molecular disorder and higher standard molar entropy at 298 K compared to ammonia. Therefore, S° for ammonia is expected to be lower than S° for nitrogen trifluoride.

Question 13

For a chemical reaction to be spontaneous only at high temperatures,which of the following conditions must be met?

Accepted Answer

The answer of For a chemical reaction to be spontaneous...

Question 14

Which of the following pairs has the member with the greater molar entropy listed first? All systems are at 25°C.

Accepted Answer

The molar entropy of a species is typically greater in the gaseous or aqueous phase compared to the solid phase, as particles have more degrees of freedom and translational energy. For choice A, the molar entropy of CO is 197.9 J/mol*K and the molar entropy of COS is 213.6 J/mol*K, so COS has the greater molar entropy. For choice B, the molar entropy of NaCl(s) is 72.1 J/mol*K and for NaCl(aq) is 72.7 J/mol*K, so NaCl(aq) has the greater molar entropy. For choice C, the molar entropy of HS(g) is 205.8 J/mol*K and for HS(aq) is 151.1 J/mol*K, so HS(g) has the greater molar entropy. For choice D, the molar entropy of Li(s) is 29.1 J/mol*K and for Pb(s) is 64.8 J/mol*K, so Pb(s) has the greater molar entropy. For choice E, the molar entropy of HS(g) is 205.8 J/mol*K and for H2S(g) is 245.7 J/mol*K, so H2S(g) has the greater molar entropy.

Question 15

For a chemical reaction to be spontaneous only at low temperatures,which of the following conditions must be met?

Accepted Answer

The answer of For a chemical reaction to be spontaneous...

Question 16

For a chemical reaction to be non-spontaneous at any temperature,which of the following conditions must be met?

Accepted Answer

The answer of For a chemical reaction to be non-spontaneous...

Question 17

Which relationship or statement best describes $\Delta$S° for the following reaction? BaCl₂(aq)+ Na₂SO₄(aq) $\to$ BaSO₄(s)+ 2NaCl(aq)

Accepted Answer

The reaction involves the formation of a solid precipitate (BaSO4), which typically results in a decrease in entropy (ΔS° < 0) because the solid is more ordered than the aqueous ions.

Question 18

Calculate $\Delta$S° for the reaction 4Cr(s)+ 3O₂(g)$\to$ 2Cr₂O₃(s)

Accepted Answer

The answer of Calculate $\Delta$S° for the reaction 4Cr(s)+ 3O₂(g)$\to$ 2Cr₂O₃(s) ...

Question 19

You are given pure samples of pentane,CH₃CH₂CH₂CH₂CH₃(l),and 1,3-pentadiene,CH₂=CHCH=CHCH₃(l).What prediction would you make concerning the standard molar entropies of pentane,S°(pentane)and 1,3-pentadiene,S°(1,3-pentadiene),at 298 K?

Accepted Answer

Pentane is a saturated hydrocarbon, while 1,3-pentadiene is an unsaturated hydrocarbon. Unsaturated hydrocarbons have more degrees of freedom than saturated hydrocarbons, so they have higher standard molar entropies.

Question 20

In order for a process to be spontaneous,

Accepted Answer

The answer of In order for a process to be...

Quiz 20: Thermodynamics: Entropy, free Energy, and the Direction of Chemical Reactions

For a chemical reaction to be spontaneous at all temperatures,which of the following conditions must be met?

Calculate $\Delta$ S° for the reaction 2Cl₂(g) + SO₂(g) $\to$ SOCl₂(g) + Cl₂O(g) $Calculate \Delta S° for the reaction 2Cl<sub>2</sub>(g) + SO<sub>2</sub>(g) \to SOCl<sub>2</sub>(g) + Cl<sub>2</sub>O(g) A) -118.2 J/K B) -104.8 J/K C) 104.8 J/K D) 118.2 J/K E) 1270.0 J/K$

In which one of these pairs will the entropy of the first substance be greater than that of the second? Assume P and T are the same for each pair,unless stated otherwise.

Calculate $\Delta$ S° for the reaction SiCl₄(g) + 2Mg(s) $\to$ 2MgCl₂(s) + Si(s) $Calculate \Delta S° for the reaction SiCl<sub>4</sub>(g) + 2Mg(s) \to 2MgCl<sub>2</sub>(s) + Si(s) A) -254.96 J/K B) -198.02 J/K C) 198.02 J/K D) 254.96 J/K E) 471.86 J/K$

For a process with $\Delta$ S < 0,which one of the following statements is correct?

You are given pure samples of ethane,C₂H₆(g) ,and toluene,C₇H₈(l) .What prediction would you make concerning their standard molar entropies at 298 K?

Consider the following quantities used in thermodynamics: E,H,q,w,S,G.How many of them are state functions?

Which relationship or statement best describes $\Delta$ S° for the following reaction? CaO(s) + CO₂(g) $\to$ CaCO₃(s)

In which one of the following pairs will the first system have a higher entropy than the second? Assume P and T are the same for each pair,unless stated otherwise.

You are given pure samples of ammonia,NH₃(g) ,and nitrogen trifluoride,NF₃(g) .What prediction would you make concerning their standard molar entropies at 298 K?

For a chemical reaction to be spontaneous only at high temperatures,which of the following conditions must be met?

Which of the following pairs has the member with the greater molar entropy listed first? All systems are at 25°C.

For a chemical reaction to be spontaneous only at low temperatures,which of the following conditions must be met?

For a chemical reaction to be non-spontaneous at any temperature,which of the following conditions must be met?

Which relationship or statement best describes $\Delta$ S° for the following reaction? BaCl₂(aq) + Na₂SO₄(aq) $\to$ BaSO₄(s) + 2NaCl(aq)

Calculate $\Delta$ S° for the reaction 4Cr(s) + 3O₂(g) $\to$ 2Cr₂O₃(s) $Calculate \Delta S° for the reaction 4Cr(s) + 3O<sub>2</sub>(g) \to 2Cr<sub>2</sub>O<sub>3</sub>(s) A) -548.1 J/K B) -147.7 J/K C) 147.7 J/K D) 310.1 J/K E) 548.1 J/K$

You are given pure samples of pentane,CH₃CH₂CH₂CH₂CH₃(l) ,and 1,3-pentadiene,CH₂=CHCH=CHCH₃(l) .What prediction would you make concerning the standard molar entropies of pentane,S°(pentane) and 1,3-pentadiene,S°(1,3-pentadiene) ,at 298 K?

In order for a process to be spontaneous,

Quiz 20: Thermodynamics: Entropy, free Energy, and the Direction of Chemical Reactions

For a chemical reaction to be spontaneous at all temperatures,which of the following conditions must be met?

Elemental boron can be formed by reaction of boron trichloride with hydrogen. BCl3(g) + 1.5H2(g) →\to→ B(s) + 3HCl(g) If Δ\DeltaΔ S° = 80.3 J/K,what is S° for BCl3(g) ?

Calculate Δ\DeltaΔ S° for the reaction 2Cl2(g) + SO2(g) →\to→ SOCl2(g) + Cl2O(g)

Calculate Δ\DeltaΔ S° for the combustion of propane. C3H8(g) + 5O2(g) →\to→ 3CO2(g) + 4H2O(g)

In which one of these pairs will the entropy of the first substance be greater than that of the second? Assume P and T are the same for each pair,unless stated otherwise.

Calculate Δ\DeltaΔ S° for the reaction SiCl4(g) + 2Mg(s) →\to→ 2MgCl2(s) + Si(s)

For a process with Δ\DeltaΔ S < 0,which one of the following statements is correct?

You are given pure samples of ethane,C2H6(g) ,and toluene,C7H8(l) .What prediction would you make concerning their standard molar entropies at 298 K?

Consider the following quantities used in thermodynamics: E,H,q,w,S,G.How many of them are state functions?

Which relationship or statement best describes Δ\DeltaΔ S° for the following reaction? CaO(s) + CO2(g) →\to→ CaCO3(s)

In which one of the following pairs will the first system have a higher entropy than the second? Assume P and T are the same for each pair,unless stated otherwise.

You are given pure samples of ammonia,NH3(g) ,and nitrogen trifluoride,NF3(g) .What prediction would you make concerning their standard molar entropies at 298 K?

For a chemical reaction to be spontaneous only at high temperatures,which of the following conditions must be met?

Which of the following pairs has the member with the greater molar entropy listed first? All systems are at 25°C.

For a chemical reaction to be spontaneous only at low temperatures,which of the following conditions must be met?

For a chemical reaction to be non-spontaneous at any temperature,which of the following conditions must be met?

Which relationship or statement best describes Δ\DeltaΔ S° for the following reaction? BaCl2(aq) + Na2SO4(aq) →\to→ BaSO4(s) + 2NaCl(aq)

Calculate Δ\DeltaΔ S° for the reaction 4Cr(s) + 3O2(g) →\to→ 2Cr2O3(s)

You are given pure samples of pentane,CH3CH2CH2CH2CH3(l) ,and 1,3-pentadiene,CH2=CHCH=CHCH3(l) .What prediction would you make concerning the standard molar entropies of pentane,S°(pentane) and 1,3-pentadiene,S°(1,3-pentadiene) ,at 298 K?

In order for a process to be spontaneous,

Calculate $\Delta$ S° for the reaction 2Cl₂(g) + SO₂(g) $\to$ SOCl₂(g) + Cl₂O(g) $Calculate \Delta S° for the reaction 2Cl<sub>2</sub>(g) + SO<sub>2</sub>(g) \to SOCl<sub>2</sub>(g) + Cl<sub>2</sub>O(g) A) -118.2 J/K B) -104.8 J/K C) 104.8 J/K D) 118.2 J/K E) 1270.0 J/K$

Calculate $\Delta$ S° for the reaction SiCl₄(g) + 2Mg(s) $\to$ 2MgCl₂(s) + Si(s) $Calculate \Delta S° for the reaction SiCl<sub>4</sub>(g) + 2Mg(s) \to 2MgCl<sub>2</sub>(s) + Si(s) A) -254.96 J/K B) -198.02 J/K C) 198.02 J/K D) 254.96 J/K E) 471.86 J/K$

For a process with $\Delta$ S < 0,which one of the following statements is correct?

You are given pure samples of ethane,C₂H₆(g) ,and toluene,C₇H₈(l) .What prediction would you make concerning their standard molar entropies at 298 K?

Which relationship or statement best describes $\Delta$ S° for the following reaction? CaO(s) + CO₂(g) $\to$ CaCO₃(s)

You are given pure samples of ammonia,NH₃(g) ,and nitrogen trifluoride,NF₃(g) .What prediction would you make concerning their standard molar entropies at 298 K?

Which relationship or statement best describes $\Delta$ S° for the following reaction? BaCl₂(aq) + Na₂SO₄(aq) $\to$ BaSO₄(s) + 2NaCl(aq)

Calculate $\Delta$ S° for the reaction 4Cr(s) + 3O₂(g) $\to$ 2Cr₂O₃(s) $Calculate \Delta S° for the reaction 4Cr(s) + 3O<sub>2</sub>(g) \to 2Cr<sub>2</sub>O<sub>3</sub>(s) A) -548.1 J/K B) -147.7 J/K C) 147.7 J/K D) 310.1 J/K E) 548.1 J/K$

You are given pure samples of pentane,CH₃CH₂CH₂CH₂CH₃(l) ,and 1,3-pentadiene,CH₂=CHCH=CHCH₃(l) .What prediction would you make concerning the standard molar entropies of pentane,S°(pentane) and 1,3-pentadiene,S°(1,3-pentadiene) ,at 298 K?