Thermodynamics
According to the Second Law of Thermodynamics, for a spontaneous process in an isolated system, the entropy must:
A
Decrease
B
Remain constant
C
Increase
D
First increase then decrease
Correct Answer:
C. Increase
Second Law states that entropy of an isolated system increases for spontaneous (irreversible) processes and remains constant only for reversible processes
In a closed system, 50 kJ of heat is added and 30 kJ of work is done by the system. The change in internal energy is:
A
20 kJ
B
-20 kJ
C
80 kJ
D
-80 kJ
From First Law: ΔU = Q - W = 50 - 30 = 20 kJ (taking work done by system as positive)
For an ideal gas, if both pressure and volume are doubled, the temperature ratio T₂/T₁ will be:
Using ideal gas law PV = nRT: T₂/T₁ = (P₂V₂)/(P₁V₁) = (2P₁ × 2V₁)/(P₁V₁) = 4
Which process is represented when a gas is compressed without any heat transfer to or from surroundings?
A
Isothermal process
B
Isobaric process
C
Adiabatic process
D
Isochoric process
Correct Answer:
C. Adiabatic process
An adiabatic process has no heat transfer (Q = 0) between the system and surroundings
Which law states that the total energy of an isolated system remains constant?
A
Second Law of Thermodynamics
B
First Law of Thermodynamics
C
Third Law of Thermodynamics
D
Zeroth Law of Thermodynamics
Correct Answer:
B. First Law of Thermodynamics
The First Law of Thermodynamics is the conservation of energy principle for thermodynamic systems
In a constant volume process (isochoric), if temperature increases from 300 K to 600 K, the pressure ratio P₂/P₁ will be:
For isochoric process: P/T = constant, so P₂/P₁ = T₂/T₁ = 600/300 = 2.0
In a Diesel cycle, which process represents constant pressure heat addition?
A
Isentropic process
B
Isobaric process
C
Isochoric process
D
Isothermal process
Correct Answer:
B. Isobaric process
The Diesel cycle has constant pressure heat addition (isobaric process) between the initial compression and subsequent expansion, distinguishing it from the Otto cycle
A heat engine operates between two thermal reservoirs at temperatures 600 K and 300 K. What is the maximum possible efficiency of this engine?
Maximum efficiency of a heat engine = 1 - (T_cold/T_hot) = 1 - (300/600) = 0.50 or 50% (Carnot efficiency)
Which of the following statements about entropy is INCORRECT?
A
Entropy is a measure of molecular disorder or randomness
B
Entropy always increases for an irreversible adiabatic process
C
Entropy of a reversible isothermal process equals Q/T
D
Entropy of the universe decreases for spontaneous processes
Correct Answer:
D. Entropy of the universe decreases for spontaneous processes
The Second Law states entropy of the universe INCREASES (ΔS_universe > 0) for spontaneous/irreversible processes, not decreases.
The relationship between specific heats Cp - Cv for an ideal gas is:
A
Cp - Cv = R
B
Cp - Cv = 2R
C
Cp = Cv (they are equal)
D
Cp - Cv = R/M where M is molar mass
Correct Answer:
A. Cp - Cv = R
Mayer's relation: Cp - Cv = R (per mole). This is fundamental for ideal gases.
