Q. In a reversible process, the work done is: (2023)
A.
Always maximum
B.
Always minimum
C.
Equal to the heat absorbed
D.
Independent of the path
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Solution
In a reversible process, the work done is always maximum compared to irreversible processes.
Correct Answer: A — Always maximum
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Q. In thermodynamics, the term 'enthalpy' is defined as: (2022)
A.
The total energy of a system
B.
The heat content of a system at constant pressure
C.
The work done by a system
D.
The change in internal energy
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Solution
Enthalpy is defined as the heat content of a system at constant pressure, represented as H = U + PV.
Correct Answer: B — The heat content of a system at constant pressure
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Q. In thermodynamics, the term 'system' refers to: (2022)
A.
The surroundings
B.
The part of the universe under study
C.
The entire universe
D.
None of the above
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Solution
In thermodynamics, the 'system' refers to the part of the universe that is being studied, while the surroundings are everything else.
Correct Answer: B — The part of the universe under study
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Q. In thermodynamics, what does the term 'enthalpy' (H) represent? (2020)
A.
Total energy of the system
B.
Energy required to break bonds
C.
Heat content of the system at constant pressure
D.
Work done by the system
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Solution
Enthalpy (H) represents the heat content of the system at constant pressure, defined as H = U + PV.
Correct Answer: C — Heat content of the system at constant pressure
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Q. In which of the following conditions does the entropy of a system increase? (2022)
A.
When a gas is compressed
B.
When a solid melts
C.
When a liquid freezes
D.
When a gas is cooled
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Solution
The entropy of a system increases when a solid melts into a liquid, as the disorder of the system increases.
Correct Answer: B — When a solid melts
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Q. In which of the following processes is the enthalpy change (ΔH) equal to the heat absorbed at constant pressure? (2019)
A.
Isothermal process
B.
Isochoric process
C.
Isobaric process
D.
Adiabatic process
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Solution
In an isobaric process, the enthalpy change (ΔH) is equal to the heat absorbed or released at constant pressure.
Correct Answer: C — Isobaric process
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Q. In which of the following processes is the enthalpy change equal to the heat absorbed by the system at constant pressure? (2019)
A.
Isothermal process
B.
Isochoric process
C.
Isobaric process
D.
Adiabatic process
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Solution
In an isobaric process, the enthalpy change is equal to the heat absorbed by the system at constant pressure.
Correct Answer: C — Isobaric process
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Q. The entropy of a perfect crystalline substance at absolute zero is given by: (2021)
A.
0 J/K
B.
1 J/K
C.
2 J/K
D.
Depends on the substance
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Solution
According to the third law of thermodynamics, the entropy of a perfect crystalline substance at absolute zero is exactly zero.
Correct Answer: A — 0 J/K
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Q. The heat capacity at constant volume (Cv) for an ideal gas is related to which of the following? (2023)
A.
Change in internal energy
B.
Change in enthalpy
C.
Change in entropy
D.
Change in Gibbs free energy
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Solution
The heat capacity at constant volume (Cv) is directly related to the change in internal energy of the system.
Correct Answer: A — Change in internal energy
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Q. The heat capacity at constant volume (Cv) is defined as: (2022)
A.
The amount of heat required to raise the temperature of a substance by 1°C at constant pressure.
B.
The amount of heat required to raise the temperature of a substance by 1°C at constant volume.
C.
The total heat content of a substance.
D.
The heat required to change the phase of a substance.
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Solution
The heat capacity at constant volume (Cv) is defined as the amount of heat required to raise the temperature of a substance by 1°C at constant volume.
Correct Answer: B — The amount of heat required to raise the temperature of a substance by 1°C at constant volume.
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Q. The heat capacity of a substance is defined as: (2023)
A.
The amount of heat required to raise the temperature of one gram by one degree Celsius.
B.
The amount of heat required to raise the temperature of one mole by one degree Celsius.
C.
The total heat content of the substance.
D.
The heat required to change the state of the substance.
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Solution
The heat capacity of a substance is defined as the amount of heat required to raise the temperature of one mole of the substance by one degree Celsius.
Correct Answer: B — The amount of heat required to raise the temperature of one mole by one degree Celsius.
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Q. What does the term 'enthalpy' (H) represent? (2019)
A.
Internal energy plus pressure-volume work
B.
Total energy of the system
C.
Heat content at constant pressure
D.
All of the above
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Solution
Enthalpy (H) represents the total heat content of a system at constant pressure and is defined as internal energy plus pressure-volume work.
Correct Answer: D — All of the above
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Q. What is the change in internal energy (ΔU) for an ideal gas during an isothermal process? (2021)
A.
ΔU = 0
B.
ΔU = nRT
C.
ΔU = -nRT
D.
ΔU = PV
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Solution
In an isothermal process for an ideal gas, the temperature remains constant, which means the internal energy does not change. Therefore, ΔU = 0.
Correct Answer: A — ΔU = 0
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Q. What is the change in internal energy (ΔU) for an ideal gas undergoing an isothermal process? (2021)
A.
ΔU = 0
B.
ΔU = Q
C.
ΔU = W
D.
ΔU = Q + W
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Solution
In an isothermal process for an ideal gas, the temperature remains constant, which means the internal energy does not change. Therefore, ΔU = 0.
Correct Answer: A — ΔU = 0
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Q. What is the change in internal energy (ΔU) for an isothermal process for an ideal gas? (2021)
A.
ΔU = 0
B.
ΔU = nRT
C.
ΔU = -nRT
D.
ΔU = PV
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Solution
In an isothermal process for an ideal gas, the temperature remains constant, which means the internal energy does not change. Therefore, ΔU = 0.
Correct Answer: A — ΔU = 0
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Q. What is the change in internal energy (ΔU) for an isothermal process of an ideal gas? (2021)
A.
ΔU = 0
B.
ΔU = nRT
C.
ΔU = -nRT
D.
ΔU = PV
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Solution
In an isothermal process for an ideal gas, the temperature remains constant, which means the internal energy does not change. Therefore, ΔU = 0.
Correct Answer: A — ΔU = 0
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Q. What is the standard enthalpy change (ΔH°) for the formation of water from its elements? (2022)
A.
-285.83 kJ/mol
B.
0 kJ/mol
C.
285.83 kJ/mol
D.
-241.82 kJ/mol
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Solution
The standard enthalpy change for the formation of water from its elements (H2 and O2) is -285.83 kJ/mol.
Correct Answer: A — -285.83 kJ/mol
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Q. What is the standard enthalpy change (ΔH°) for the reaction: C(s) + O2(g) → CO2(g)? (2022)
A.
It is always positive.
B.
It is always negative.
C.
It can be zero.
D.
It depends on the temperature.
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Solution
The standard enthalpy change for combustion reactions, such as the formation of CO2 from carbon and oxygen, is typically negative, indicating that the reaction is exothermic.
Correct Answer: B — It is always negative.
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Q. Which of the following is NOT a characteristic of an exothermic reaction? (2019)
A.
Releases heat
B.
ΔH is negative
C.
Temperature of the surroundings increases
D.
Absorbs energy from the surroundings
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Solution
An exothermic reaction releases heat and has a negative ΔH. It causes the temperature of the surroundings to increase, not absorb energy.
Correct Answer: D — Absorbs energy from the surroundings
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Q. Which of the following is true about exothermic reactions? (2022)
A.
They absorb heat.
B.
They release heat.
C.
They have a positive ΔH.
D.
They are always spontaneous.
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Solution
Exothermic reactions release heat to the surroundings, resulting in a negative change in enthalpy (ΔH < 0).
Correct Answer: B — They release heat.
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Q. Which of the following processes increases the entropy of the system? (2022)
A.
Freezing of water
B.
Melting of ice
C.
Condensation of steam
D.
Compression of gas
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Solution
The melting of ice increases the entropy of the system as it transitions from a solid to a liquid state, which has more disorder.
Correct Answer: B — Melting of ice
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