Thermodynamics Concept Questions (Fully Unique – All 35)
1. According to the Second Law of Thermodynamics, not all energy changes result in spontaneous
processes. A process is considered spontaneous if it can occur without continuous external input. Which of the following best describes a spontaneous process?
A. It always absorbs heat
B. It always decreases entropy
C. It increases the total entropy of the universe
D. It requires external work
2. Heat does not naturally move from cold to hot objects without external work being done. This behavior is expressed by a specific formulation of the Second Law of Thermodynamics. Which statement corresponds to this idea?
A. First Law
B. Clausius Statement
C. Kelvin Statement
D. Third Law
3. In an isolated system undergoing a spontaneous process, no energy or matter enters or leaves. Yet internal rearrangements result in a directional change governed by a thermodynamic property. What happens to the entropy in such a case?
A. It decreases
B. It remains constant
C. It increases
D. It becomes negative
4. Entropy is a property that depends only on the current state of the system, not on the path taken. It measures the extent of molecular disorder or randomness. Which of the following is a state function that increases with disorder?
A. Enthalpy
B. Entropy
C. Work
D. Heat
5. For a reversible process, the entropy change is proportional to the heat transferred and inversely proportional to the temperature. This relationship allows entropy to be quantitatively defined for such ideal processes. What is the correct expression for this change?
A. dS = dq/T
B. dS = dqT
C. dS = PdV
D. dS = dU/T
6. During a reversible isothermal expansion of an ideal gas, the temperature remains fixed while the gas volume increases. This expansion allows the system to absorb heat, increasing its entropy. How does the entropy of the system behave?
A. Decreases
B. Remains constant
C. Increases
D. Reaches zero
7. In a free expansion into a vacuum, a gas does not exchange heat or do work. However, since the gas spreads out over a larger volume, its entropy increases.
What happens to the entropy of the surroundings?
A. Increases
B. Decreases
C. Remains zero
D. Cannot be calculated
8. Phase changes such as vaporization or fusion involve entropy changes due to changes in molecular order.
In which of the following processes would you expect the greatest increase in entropy?
A. Water freezingB. Steam condensing
C. Alcohol evaporating
D. Gas compression
9. The Third Law of Thermodynamics defines the entropy of a perfect crystal at absolute zero. At this temperature, the system should be in a perfectly ordered state with no randomness.
What is the entropy value for such a system?
A. Maximum
B. Zero
C. Undefined
D. Negative
10. A Carnot engine operates on a reversible cycle between two thermal reservoirs. It performs work while transferring heat in a perfectly efficient manner.
What is the net entropy change in the complete Carnot cycle?
A. Positive
B. Negative
C. Zero
D. Undefined
11. The statistical definition of entropy explains it in terms of the number of microstates available to a system. According to Boltzmann, entropy increases as the number of accessible arrangements increases.
Which equation reflects this idea?
A. S = k ln W
B. S = H/T
C. S = PV/T
D. S = q/T
12. Helmholtz free energy represents the maximum work extractable from a system at constant volume and temperature. It becomes particularly useful in closed systems doing non-expansion work.
Which expressiondefines Helmholtz energy?
A. A = U – TS
B. A = H – TS
C. A = q – PdV
D. A = T + U
13. Gibbs free energy is used to determine the spontaneity of a reaction at constant pressure and temperature. A negative change in Gibbs energy indicates a spontaneous process.
What happens to Gibbs free energy during a spontaneous reaction?
A. It increases
B. It remains zero
C. It decreases
D. It oscillates
14. At equilibrium, there is no net driving force in a chemical reaction. This condition corresponds to a particular value of Gibbs free energy change.
Which value reflects equilibrium?
A. Delta G < 0
B. Delta G = 0
C. Delta G > 0
D. Delta G = Delta H – T Delta S
15. Troutons rule estimates the entropy of vaporization for many non-associated liquids. It suggests a nearly constant value for Delta S_vap at the boiling point.
Which is closest to this value?
A. 85 J/molK
B. 10 J/molK
C. 200 J/molK
D. 273 J/molK
16. As temperature increases, molecules access more energy levels. This raises the number of microstates available to the system.
What is the thermodynamic result of this effect?
A. Enthalpy decreases
B. Entropy increases
C. Volume decreases
D. Pressure becomes negative
17. Calorimetry can be used to calculate entropy changes through heat measurements. At constant pressure, the relationship between heat and temperature yields the entropy change.
Which formula applies?
A. Delta S = Cp ln(Tf/Ti)
B. Delta S = Cv(Tf – Ti)
C. Delta S = qrev x T
D. Delta S = P/T
18. During isothermal expansion of an ideal gas, work is done by the system while internal energy remains constant. Entropy increases as the gas occupies more space.
What expression gives this entropy change?
A. nR ln(Vf/Vi)
B. nR(Tf – Ti)
C. Cp(Tf – Ti)
D. P Delta V
19. The standard molar entropy of ions in solution is difficult to measure directly. By convention, the entropy of H(aq) is assigned a value of zero.
What is the reason for this choice?
A. It is the least stable ion
B. It simplifies calculations
C. It reflects experimental measurements
D. It is energetically neutral
20. The entropy change of the surroundings depends on the direction of heat transfer. If a system releases heat into the surroundings, their entropy increases.
What is the equation for this change?
A. Delta S_sur = -q_sys / T
B. Delta S_sur = T/qC. Delta S_sur = q / P
D. Delta S_sur = -T q
21. In melting, the ordered structure of a solid becomes disordered as it transforms into a liquid. This transformation increases entropy significantly.
Which process involves the greatest entropy gain?
A. Freezing
B. Sublimation
C. Condensation
D. Crystallization
22. During a spontaneous reaction at constant pressure, the enthalpy and entropy changes compete. If both are negative, the reaction may still proceed under the right conditions.
What factor determines spontaneity in this case?
A. Volume
B. Temperature
C. Pressure
D. Gibbs free energy
23. The Clausius inequality shows that real processes generate entropy. This inequality generalizes the Second Law to both reversible and irreversible processes.
Which mathematical condition reflects this idea?
A. dS >= dq/T
B. dU = q + w
C. dS = qrev/T
D. dq = dw
24. When a gas expands into a vacuum, no heat or work is exchanged, but the number of configurations increases. This results in an increase in entropy.
What type of process is this?
A. Adiabatic
B. Isothermal
C. IrreversibleD. Reversible
25. The entropy of a system is independent of the path taken between two states. Instead, it depends only on the initial and final states.
What kind of function is entropy?
A. Path function
B. State function
C. External function
D. Kinetic function
26. Entropy increases when a liquid evaporates into a gas due to increased freedom of motion. This transformation occurs spontaneously under appropriate conditions.
Which change best illustrates this concept?
A. Liquid to solid
B. Gas to liquid
C. Solid to gas
D. Gas to plasma
27. The entropy change during a phase transition at constant pressure can be calculated using enthalpy. This applies to melting, vaporization, and other transitions.
What equation is used?
A. Delta S = Delta H / T
B. Delta S = Cp ln(T2/T1)
C. Delta S = qrev x T
D. Delta S = P Delta V
28. At absolute zero, a perfect crystal has only one microstate. This leads to zero entropy according to the Third Law of Thermodynamics.
What does this imply about disorder at 0 K?
A. Minimal
B. Infinite
C. Undefined
D. Constant
29. A gas at high temperature has more available energy levels. This means the number of possible configurations increases.
What is the effect on entropy?
A. Decreases
B. Remains constant
C. Increases
D. Becomes negative
30. Entropy and enthalpy together determine the spontaneity of a process. This relationship is captured in the Gibbs free energy equation.
Which formula expresses this concept?
A. G = H – TS
B. G = U + PV
C. G = T – S
D. G = H + TS
31. For a process to be spontaneous at constant T and P, Gibbs energy must decrease. This thermodynamic criterion helps predict chemical reaction directions.
Which inequality is true?
A. Delta G < 0
B. Delta G = 0
C. Delta G > 0
D. Delta G = T Delta S
32. Entropy changes can be estimated from heat capacity data over a temperature range. This approach is useful when direct measurement is not possible.
What is the corresponding integral expression?
A. S = (Cp/T) dT
B. S = qrev dT
C. S = PdV
D. S = TdS
33. Gibbs energy combines enthalpy and entropy effects into one potential. It is minimized at equilibrium under constant T and P.
Which of the following is true at equilibrium?A. Delta G > 0
B. Delta G = 0
C. Delta G < 0
D. Delta G = Delta H + T Delta S
34. The entropy of mixing increases as substances are combined. This is especially pronounced in ideal gases.
What thermodynamic variable reflects this disorder?
A. Enthalpy
B. Volume
C. Entropy
D. Internal energy
35. As molecules become more disordered, the number of accessible microstates increases.
This corresponds to a higher entropy. What term defines this property?
A. Entropy
B. Free energy
C. Enthalpy
D. Pressure
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