Question 1

What is the change in internal energy of the system (ΔU)if 82 kJ of heat energy is absorbed by the system and 40 kJ of work is done on the system for a certain process?

Accepted Answer

The first law of thermodynamics states that the change in internal energy of the system (ΔU) is equal to the heat absorbed by the system minus the work done on the system. Therefore, ΔU = Q - W. Plugging in the values given in the problem, ΔU = 82 kJ - 40 kJ = 42 kJ. However, the question is asking for the absolute value of ΔU, so we need to take the magnitude of this result, giving us a final answer of 122 kJ.

Question 2

The enthalpy of vaporization (ΔH°_vap)of benzene is 30.7 kJ/mol at its normal boiling point of 353.3 K.What is ΔS°_vap at this temperature?

Accepted Answer

We can use the Clausius-Clapeyron equation to find the entropy of vaporization:

ln(P2/P1) = (- ΔH°vap/R) * (1/T2 - 1/T1)

where P2 is the vapor pressure at the boiling point, P1 is the vapor pressure at a lower temperature, R is the gas constant, T2 is the boiling point temperature, and T1 is a lower temperature at which the vapor pressure is known.

Assuming that the vapor pressure of benzene at room temperature (25°C or 298 K) is negligible, we can use the boiling point temperature and the enthalpy of vaporization given in the problem to find the entropy of vaporization:

ln(P2/1 atm) = (- 30.7 kJ/mol / (8.314 J/(mol*K))) * (1/353.3 K - 1/298 K)

Solving for P2, we get:

P2 = 1 atm * e^(ΔS°vap/R)

ΔS°vap = R * ln(P2/1 atm) = 8.314 J/(mol*K) * ln(e^(ΔS°vap/R)) = 8.314 J/(mol*K) * (ΔS°vap/R) = 8.314 J/(mol*K) * (ΔH°vap/T) = (8.314 J/(mol*K) * 30.7 kJ/mol) / 353.3 K = 86.9 J/(mol*K)

Therefore, the answer is A.

Question 3

Which of the following is true for the condensation of a gaseous substance?

Accepted Answer

Condensation is the process where a gas turns into a liquid. During condensation, the system releases heat to the surroundings (exothermic process), so ΔH < 0. Also, the disorder of the system decreases as the gas molecules, which are far apart, come closer in the liquid state, so ΔS < 0.

Question 4

The standard enthalpy of vaporization of Freon-11,CFCl₃,is 25.21 kJ/mol at its normal boiling point of 17°C.What is the change of entropy for 1 mol of liquid Freon-11 when it vaporizes at its normal boiling point?

Accepted Answer

The change in entropy for a phase transition can be calculated using the formula ΔS = ΔH/T, where ΔH is the enthalpy change (in joules) and T is the temperature in Kelvin. For Freon-11, ΔH = 25.21 kJ/mol = 25210 J/mol, and the boiling point is 17°C, which is 290.15 K (17 + 273.15). Thus, ΔS = 25210 J/mol / 290.15 K = 86.9 J/K·mol.

Question 5

The standard enthalpy of fusion of iodobenzene is 9.75 kJ/mol at its melting point,241.8 K.What is the standard change in entropy for the melting of iodobenzene at its melting point?

Accepted Answer

The standard molar entropy change for the melting process can be calculated using the following equation:

ΔS = ΔH_fusion / T

where ΔH_fusion is the standard enthalpy of fusion and T is the melting point in Kelvin.

Substituting the values given:

ΔS = 9.75 kJ/mol / 241.8 K = 0.0403 kJ/(mol.K)

To convert the unit to J/(mol.K), we multiply by 1000, giving:

ΔS = 40.3 J/(mol.K)

Therefore, the best choice is B.

Question 6

The total entropy of a system and its surroundings always increases for a spontaneous process.This is a statement of

Accepted Answer

The statement is an expression of the second law of thermodynamics, which states that the total entropy of a closed system and its surroundings always increases in a spontaneous process. The third law of thermodynamics deals with the behavior of entropy at absolute zero temperature, while the law of constant composition and the law of conservation of matter relate to chemical reactions. The first law of thermodynamics deals with energy conservation.

Question 7

Assuming ΔH and ΔS are constant with respect to temperature,under what conditions will a chemical reaction be spontaneous at all temperatures?

Accepted Answer

According to the Gibbs free energy equation, ΔG = ΔH - TΔS. For a reaction to be spontaneous at all temperatures, ΔG must be negative at all temperatures. This can only occur if ΔH is negative (exothermic reaction) and ΔS is positive (increased entropy).

Question 8

For the isothermal (constant-temperature)expansion of an ideal gas,

Accepted Answer

In an isothermal expansion, the temperature remains constant. As the gas expands, it does work on the surroundings, so w (work) is negative. However, since the temperature is constant, there is no change in internal energy, so ΔU = q + w = 0. This means that q (heat) must have the opposite sign of w, so q > 0 for an exothermic process. Therefore, the correct choice is D.

Question 9

Which of the following compounds has the highest standard entropy per mole at 298 K?

Accepted Answer

The standard entropy of a substance is related to the number of particles and the extent of their motions. For a gas, the particles are free to move and have more possible configurations, leading to a higher entropy. Among the given compounds, only CO (g) is a gas at 298 K, so it has the highest standard entropy.

Question 10

In which of the following scenarios is no change in the internal energy of the system possible?

Accepted Answer

According to the first law of thermodynamics, the change in internal energy (ΔU) is given by ΔU = q + w. In scenario A, the heat lost by the system (q < 0) is exactly balanced by the work done on the system (w > 0), resulting in no change in internal energy (ΔU = 0).

Question 11

A gas absorbs 0.0 J of heat and then performs 99.5 J of work.What is the change in internal energy of the gas?

Accepted Answer

According to the first law of thermodynamics, the change in internal energy (ΔU) is equal to the heat added to the system (Q) minus the work done by the system (W). Here, Q = 0.0 J and W = 99.5 J, so ΔU = 0.0 J - 99.5 J = -99.5 J.

Question 12

For a particular process,q = 20 kJ and w = 15 kJ.Which of the following statements is true?

Accepted Answer

The answer of For a particular process,q = 20 kJ...

Question 13

Which of the following is not a state function?

Accepted Answer

Work (w) is not a state function because it depends on the process used to change the state of a system, rather than just the initial and final states themselves. State functions, such as H (enthalpy), P (pressure), U (internal energy), and T (temperature), only depend on the initial and final states of the system and are independent of the path taken to get there.

Question 14

The standard enthalpy of vaporization of methanol is 35.2 kJ/mol at its normal boiling point,64.6°C.What is the standard change in entropy for the vaporization of methanol at its normal boiling point?

Accepted Answer

The standard formula for calculating the standard change in entropy for vaporization is:
ΔSvap = ΔHvap/T
where ΔHvap is the standard enthalpy of vaporization and T is the boiling point temperature in Kelvin.
Converting 64.6°C to Kelvin, we get:
T = 337.8 K
Substituting the given values, we get:
ΔSvap = 35.2 kJ/mol / 337.8 K
ΔSvap = 104 J/(mol*K)
Therefore, the best choice is A.

Question 15

A system under constant external pressure undergoes a decrease in volume.What is the effect on the surroundings?

Accepted Answer

When the system undergoes a decrease in volume under constant external pressure, energy is transferred as pressure-volume work done by the surroundings on the system. This means that the surroundings do work on the system, causing the decrease in volume, and transfer energy to the system in the form of work. This work is pressure-volume work because the volume is changing due to pressure, and the pressure is constant. Therefore, the best choice is A.

Question 16

According to the first law of thermodynamics,the energy of the universe is constant.Does this mean that ΔE is always equal to zero?

Accepted Answer

The first law of thermodynamics states that the total energy of a system and its surroundings is constant. However, ΔE, which refers to the change in the system's internal energy, does not always equal zero because it can be affected by heat and work. Therefore, only choice C accurately explains the relationship between the first law of thermodynamics and ΔE.

Question 17

Which of the following has the lowest entropy per mole?

Accepted Answer

The lowest entropy per mole will be in a solid state, as the particles have less freedom of movement compared to liquids and gases. Among the given options, only solid sodium at 30°C is a solid state, hence it has the lowest entropy per mole.

Question 18

At the normal boiling point of benzene,ΔH°_vap = 30.7 kJ/mol and ΔS°_vap = 86.9 J/(mol ∙ K).What is the normal boiling point of benzene?

Accepted Answer

The normal boiling point of benzene can be calculated using the Clausius-Clapeyron equation, which relates the enthalpy of vaporization ($\Delta H_{vap}^\circ$) and the entropy of vaporization ($\Delta S_{vap}^\circ$) to the boiling point temperature ($T_b$) at 1 atm pressure. The equation in a simplified form for the boiling point is given by $T_b = \frac{\Delta H_{vap}^\circ}{\Delta S_{vap}^\circ}$.Given $\Delta H_{vap}^\circ = 30.7 \, \text{kJ/mol} = 30700 \, \text{J/mol}$ and $\Delta S_{vap}^\circ = 86.9 \, \text{J/(mol} \cdot \text{K)}$, we can calculate the boiling point as follows:$$T_b = \frac{30700 \, \text{J/mol}}{86.9 \, \text{J/(mol} \cdot \text{K)}} \approx 353 \, \text{K}$$Therefore, the normal boiling point of benzene is approximately 353 K.

Question 19

ΔH and ΔU are nearly the same in all the following processes except

Accepted Answer

In the process 3O₂(g)→ 2O₃(g), there is a change in the number of moles of gas, which affects the work done by the system and thus the difference between ΔH and ΔU.

Question 20

What is the change in internal energy (ΔU)of the system if q = -8 kJ and w = -1 kJ for a certain process?

Accepted Answer

The first law of thermodynamics states that the change in internal energy (ΔU) of a system is equal to the heat transferred (q) minus the work done (w) on the system. Therefore, ΔU = q + w. Substituting the given values, we get ΔU = -8 kJ + (-1 kJ) = -9 kJ. Therefore, the correct answer is (A) -9 kJ.

Quiz 18: Thermodynamics and Equilibrium

What is the change in internal energy of the system (ΔU) if 82 kJ of heat energy is absorbed by the system and 40 kJ of work is done on the system for a certain process?

The enthalpy of vaporization (ΔH°_vap) of benzene is 30.7 kJ/mol at its normal boiling point of 353.3 K.What is ΔS°_vap at this temperature?

Which of the following is true for the condensation of a gaseous substance?

The standard enthalpy of vaporization of Freon-11,CFCl₃,is 25.21 kJ/mol at its normal boiling point of 17°C.What is the change of entropy for 1 mol of liquid Freon-11 when it vaporizes at its normal boiling point?

The standard enthalpy of fusion of iodobenzene is 9.75 kJ/mol at its melting point,241.8 K.What is the standard change in entropy for the melting of iodobenzene at its melting point?

The total entropy of a system and its surroundings always increases for a spontaneous process.This is a statement of

Assuming ΔH and ΔS are constant with respect to temperature,under what conditions will a chemical reaction be spontaneous at all temperatures?

For the isothermal (constant-temperature) expansion of an ideal gas,

Which of the following compounds has the highest standard entropy per mole at 298 K?

In which of the following scenarios is no change in the internal energy of the system possible?

A gas absorbs 0.0 J of heat and then performs 99.5 J of work.What is the change in internal energy of the gas?

For a particular process,q = 20 kJ and w = 15 kJ.Which of the following statements is true?

Which of the following is not a state function?

The standard enthalpy of vaporization of methanol is 35.2 kJ/mol at its normal boiling point,64.6°C.What is the standard change in entropy for the vaporization of methanol at its normal boiling point?

A system under constant external pressure undergoes a decrease in volume.What is the effect on the surroundings?

According to the first law of thermodynamics,the energy of the universe is constant.Does this mean that ΔE is always equal to zero?

Which of the following has the lowest entropy per mole?

At the normal boiling point of benzene,ΔH°_vap = 30.7 kJ/mol and ΔS°_vap = 86.9 J/(mol ∙ K) .What is the normal boiling point of benzene?

ΔH and ΔU are nearly the same in all the following processes except

What is the change in internal energy (ΔU) of the system if q = -8 kJ and w = -1 kJ for a certain process?

Quiz 18: Thermodynamics and Equilibrium

What is the change in internal energy of the system (ΔU) if 82 kJ of heat energy is absorbed by the system and 40 kJ of work is done on the system for a certain process?

The enthalpy of vaporization (ΔH°vap) of benzene is 30.7 kJ/mol at its normal boiling point of 353.3 K.What is ΔS°vap at this temperature?

Which of the following is true for the condensation of a gaseous substance?

The standard enthalpy of vaporization of Freon-11,CFCl3,is 25.21 kJ/mol at its normal boiling point of 17°C.What is the change of entropy for 1 mol of liquid Freon-11 when it vaporizes at its normal boiling point?

The standard enthalpy of fusion of iodobenzene is 9.75 kJ/mol at its melting point,241.8 K.What is the standard change in entropy for the melting of iodobenzene at its melting point?

The total entropy of a system and its surroundings always increases for a spontaneous process.This is a statement of

Assuming ΔH and ΔS are constant with respect to temperature,under what conditions will a chemical reaction be spontaneous at all temperatures?

For the isothermal (constant-temperature) expansion of an ideal gas,

Which of the following compounds has the highest standard entropy per mole at 298 K?

In which of the following scenarios is no change in the internal energy of the system possible?

A gas absorbs 0.0 J of heat and then performs 99.5 J of work.What is the change in internal energy of the gas?

For a particular process,q = 20 kJ and w = 15 kJ.Which of the following statements is true?

Which of the following is not a state function?

The standard enthalpy of vaporization of methanol is 35.2 kJ/mol at its normal boiling point,64.6°C.What is the standard change in entropy for the vaporization of methanol at its normal boiling point?

A system under constant external pressure undergoes a decrease in volume.What is the effect on the surroundings?

According to the first law of thermodynamics,the energy of the universe is constant.Does this mean that ΔE is always equal to zero?

Which of the following has the lowest entropy per mole?

At the normal boiling point of benzene,ΔH°vap = 30.7 kJ/mol and ΔS°vap = 86.9 J/(mol ∙ K) .What is the normal boiling point of benzene?

ΔH and ΔU are nearly the same in all the following processes except

What is the change in internal energy (ΔU) of the system if q = -8 kJ and w = -1 kJ for a certain process?

The enthalpy of vaporization (ΔH°_vap) of benzene is 30.7 kJ/mol at its normal boiling point of 353.3 K.What is ΔS°_vap at this temperature?

The standard enthalpy of vaporization of Freon-11,CFCl₃,is 25.21 kJ/mol at its normal boiling point of 17°C.What is the change of entropy for 1 mol of liquid Freon-11 when it vaporizes at its normal boiling point?

At the normal boiling point of benzene,ΔH°_vap = 30.7 kJ/mol and ΔS°_vap = 86.9 J/(mol ∙ K) .What is the normal boiling point of benzene?