A reversible process between two states A and B will have entropy change:
A
Greater than that of an irreversible process between same states
B
Less than that of an irreversible process between same states
C
Equal to that of any path between same states
D
Dependent on the type of process
Correct Answer:
C. Equal to that of any path between same states
Entropy is a state function. ΔS is path-independent and same for all processes (reversible or irreversible) between fixed states.
For a constant pressure process, the heat absorbed equals:
A
Change in internal energy
B
Change in enthalpy
C
Change in entropy
D
Work done by system
Correct Answer:
B. Change in enthalpy
At constant pressure: ΔH = Q_p (definition of enthalpy). From ΔU = Q - W and W = PΔV, we get Q = ΔH.
The compressibility factor Z for a real gas at high pressures is typically:
A
Greater than 1 (repulsive forces dominate)
B
Less than 1 (attractive forces dominate)
C
Equal to 1
D
Always greater than 2
Correct Answer:
A. Greater than 1 (repulsive forces dominate)
At high pressures, molecular volume effect (b term) dominates, making Z > 1. At moderate pressures, Z < 1 due to intermolecular attractions.
For a binary ideal solution, Raoult's law states that:
A
Partial pressure of each component = mole fraction × vapor pressure of pure component
B
Total pressure = sum of mole fractions × atmospheric pressure
C
Activity coefficient of each component = 1
D
Vapor pressure is independent of composition
Correct Answer:
A. Partial pressure of each component = mole fraction × vapor pressure of pure component
Raoult's law: P_i = x_i × P_i° for ideal solutions. Both statements A and C are equivalent for ideal solutions.
The Joule-Thomson coefficient μ_JT is negative for most gases at room temperature. This means:
A
Temperature increases during expansion
B
Temperature decreases during expansion
C
No temperature change occurs
D
Entropy decreases during expansion
Correct Answer:
A. Temperature increases during expansion
μ_JT = (∂T/∂P)_H. Negative coefficient means T increases with pressure drop (cooling requires very low T or high P).
In an adiabatic compression process for an ideal gas, which statement is correct?
A
Temperature remains constant
B
Work done equals change in internal energy
C
Entropy increases
D
Heat capacity is zero
Correct Answer:
B. Work done equals change in internal energy
For adiabatic process, Q = 0, so ΔU = W (first law). Temperature increases during compression.
The Maxwell relation derived from dG = -SdT + VdP is:
A
(∂S/∂P)_T = (∂V/∂T)_P
B
(∂S/∂P)_T = -(∂V/∂T)_P
C
(∂S/∂T)_P = (∂V/∂P)_T
D
(∂V/∂T)_P = (∂P/∂S)_V
Correct Answer:
B. (∂S/∂P)_T = -(∂V/∂T)_P
From dG = -SdT + VdP, cross derivatives give (∂S/∂P)_T = -(∂V/∂T)_P, a Maxwell relation.
For a spontaneous adiabatic process in an isolated system, entropy must:
A
Decrease
B
Remain constant
C
Increase or remain constant
D
Equal zero
Correct Answer:
C. Increase or remain constant
Second law: dS_universe ≥ 0. For isolated systems, dS_system ≥ 0. Equality holds for reversible adiabatic processes.
In a throttling process (Joule-Thomson expansion), which property remains constant?
A
Temperature
B
Enthalpy
C
Entropy
D
Internal energy
Correct Answer:
B. Enthalpy
Throttling through a valve occurs at constant enthalpy (isenthalpic process). This explains cooling of real gases during expansion.
The work done by a system during expansion against constant external pressure P_ext is:
A
W = nRT ln(V_f/V_i)
B
W = P_ext(V_f - V_i)
C
W = ∫P_int dV
D
W = ΔH - TΔS
Correct Answer:
B. W = P_ext(V_f - V_i)
For constant external pressure, work is W = P_ext × ΔV. This is path-dependent work for irreversible processes.
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