Thermodynamics MCQ: Online Free MCQ test with Answers

Thermodynamics physics MCQs with Answers

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1. Heat cannot by itself flow from a body at a lower temperature to a body at a higher temperature” is a statement or consequence of:

A. The second law of thermodynamics

B. Conservation of momentum

C. Conservation of mass

D. The first law of thermodynamics

The correct answer is A. The second law of thermodynamics.

Explanation:
This statement reflects the second law of thermodynamics, which asserts that heat flows naturally from hot to cold bodies in an isolated system.

2. Which of the following is incorrect regarding the first law of thermodynamics?

A. It introduces the concept of internal energy

B. It introduces the concept of entropy

C. It is not applicable to any cyclic process

D. It is a restatement of the principle of conservation of energy

The correct answers are B and C.

Explanation:
The first law relates to internal energy and conservation of energy, not entropy, and is applicable to cyclic processes.

3. Which of the following statements is correct for any thermodynamic system?

A. The internal energy changes in all processes

B. Internal energy and entropy are state functions

C. The change in entropy can never be zero

D. The work done in an adiabatic process is always zero

The correct answer is B. Internal energy and entropy are state functions.

Explanation:
State functions depend only on the system's state, not on the path taken.

4. Which of the following parameters does not characterize the thermodynamic state of matter?

A. Temperature

B. Pressure

C. Work

D. Volume

The correct answer is C. Work.

Explanation:
Work depends on the process path, unlike temperature, pressure, and volume, which characterize state.

5. Even a Carnot engine cannot give 100% efficiency because we cannot:

A. Prevent radiation

B. Find ideal sources

C. Reach absolute zero temperature

D. Eliminate friction

The correct answer is C. Reach absolute zero temperature.

Explanation:
Achieving absolute zero is theoretically impossible, limiting the Carnot engine's efficiency.

6. Which statement is incorrect?

A. All reversible cycles have the same efficiency

B. The reversible cycle has more efficiency than an irreversible one

C. Carnot cycle is a reversible one

D. Carnot cycle has the maximum efficiency in all cycles

The correct answer is A. All reversible cycles have the same efficiency.

Explanation:
Efficiency depends on the temperature range, so not all reversible cycles have the same efficiency.

7. A Carnot engine operating between temperatures \( T_1 \) and \( T_2 \) has efficiency \( \frac{1}{6} \). When \( T_2 \) is lowered by 62 K, its efficiency increases to \( \frac{1}{3} \). Then \( T_1 \) and \( T_2 \) are, respectively:

A. 372 K and 310 K

B. 372 K and 330 K

C. 330 K and 268 K

D. 310 K and 248 K

The correct answer is A. 372 K and 310 K.

Explanation:
Calculating based on efficiency formulas, the temperatures are determined to be 372 K and 310 K.

8. 100 g of water is heated from 30 °C to 50 °C. Ignoring the slight expansion of water, the change in its internal energy is (specific heat of water is 4184 J/kg·K):

A. 4.2 kJ

B. 8.4 kJ

C. 84 kJ

D. 2.1 kJ

The correct answer is B. 8.4 kJ.

Explanation:
Using \( \Delta U = m \cdot c \cdot \Delta T \), the internal energy change is calculated as 8.4 kJ.

9. 200 g of water is heated from 40 °C to 60 °C. Ignoring the slight expansion of water, the change in its internal energy is close to (specific heat of water = 4184 J/kg·K):

A. 167.4 kJ

B. 8.4 kJ

C. 4.2 kJ

D. 16.7 kJ

The correct answer is D. 16.7 kJ.

Explanation:
Calculating \( \Delta U \) with \( m = 0.2 \) kg and \( \Delta T = 20 \) °C yields 16.7 kJ.

10. The work of 146 kJ is performed to compress one-kilomole of gas adiabatically, raising its temperature by 7ºC. The gas is:

A. Monoatomic

B. Diatomic

C. Triatomic

D. A mixture of monoatomic and diatomic gases

The correct answer is B. Diatomic.

Explanation:
The temperature change and work relation is consistent with a diatomic gas's properties.

11. From the following statements concerning an ideal gas at a given temperature \( T \), select the correct one:

A. The coefficient of volume expansion at constant pressure is the same for all ideal gases

B. The average translational kinetic energy per molecule of oxygen gas is \( 3kT \), where \( k \) is the Boltzmann constant

C. The mean free path of molecules increases with an increase in pressure

D. In a gaseous mixture, the average translational kinetic energy of the molecules of each component is different

The correct answer is A. The coefficient of volume expansion at constant pressure is the same for all ideal gases.

Explanation:
The coefficient of expansion for all ideal gases is the same at constant pressure, as per Charles' law.

12. Calorie is defined as the amount of heat required to raise the temperature of 1 g of water by 1 °C under which of the following conditions?

A. From 14.5 °C to 15.5 °C at 760 mm of Hg

B. From 98.5 °C to 99.5 °C at 760 mm of Hg

C. From 13.5 °C to 14.5 °C at 76 mm of Hg

D. From 3.5 °C to 4.5 °C at 76 mm of Hg

The correct answer is A. From 14.5 °C to 15.5 °C at 760 mm of Hg.

Explanation:
This standard condition is used to define the calorie as a unit of heat.

13. The average translational kinetic energy of \( \text{O}_2 \) (molar mass 32) molecules at a particular temperature is 0.048 eV. The translational kinetic energy of \( \text{N}_2 \) (molar mass 28) molecules in eV at the same temperature is:

A. 0.0015

B. 0.003

C. 0.048

D. 0.768

The correct answer is C. 0.048.

Explanation:
Translational kinetic energy for ideal gases depends on temperature, not molecular mass, so it remains the same.

14. An ideal gas heat engine is operating between 227 °C and 127 °C. It absorbs \( 10^4 \, \text{J} \) of heat at a higher temperature. The amount of heat converted into work is:

A. 2000 J

B. 4000 J

C. 8000 J

D. 5600 J

The correct answer is A. 2000 J.

Explanation:
Using efficiency \( \eta = 1 - \frac{T_2}{T_1} \), we find the heat converted to work as 2000 J.

15. One mole of a monoatomic gas is heated at a constant pressure of 1 atmosphere from 0 K to 100 K. If the gas constant \( R = 8.32 \, \text{J/mol·K} \), the change in internal energy of the gas is approximately:

A. 2.3 J

B. 46 J

C. \( 8.67 \times 10^3 \, \text{J} \)

D. \( 1.25 \times 10^3 \, \text{J} \)

The correct answer is D. \( 1.25 \times 10^3 \, \text{J} \).

Explanation:
Using \( \Delta U = \frac{3}{2} n R \Delta T \), the internal energy change is calculated as \( 1.25 \times 10^3 \, \text{J} \).

16. Refer to a thermodynamic process diagram and match the following processes:
P: Process I - a) Adiabatic
Q: Process II - b) Isobaric
R: Process III - c) Isochoric
S: Process IV - d) Isothermal

A. (P,c), (Q,d), (R,b), (S,a)

B. (P,c), (Q,d), (R,b), (S,a)

C. (P,a), (Q,c), (R,d), (S,b)

D. (P,c), (Q,a), (R,d), (S,b)

The correct answer is D. (P,c), (Q,a), (R,d), (S,b).

Explanation:
This matches the thermodynamic processes correctly based on their characteristics.

17. Which of the following processes can be used to perform the maximum work on an ideal gas if it is compressed to half its initial volume?

A. Isothermal

B. Isochoric

C. Isobaric

D. Adiabatic

The correct answer is D. Adiabatic.

Explanation:
In adiabatic compression, all work contributes to changing the internal energy, maximizing the work done.

18. The coefficient of performance of a refrigerator is 5. If the temperature inside the freezer is -20℃, calculate the heat rejected to the surroundings.

A. 11℃

B. 41℃

C. 21℃

D. 31℃

The correct answer is D. 31℃.

Explanation:
Using the coefficient of performance, the surrounding temperature is found to be 31°C.

19. A thermodynamic system is represented with a graph ABCD. What is the heat rejected by the system during the cycle?

A. \( pV \)

B. \( 2pV \)

C. \( 4pV \)

D. \( \frac{1}{2} pV \)

The correct answer is B. \( 2pV \).

Explanation:
By examining the area under the curve in a PV diagram, the heat rejected is calculated to be \( 2pV \).

20. Which of the following statements is incorrect?

A. For the triple point of water, \( 1°K = \frac{1}{273.16} \)

B. The first law of thermodynamics is also known as the law of thermal equilibrium

C. The triple point of water is one of the reference points on the thermodynamic scale of temperature

D. At room temperature, the heat of combustion is not found

The correct answer is D. At room temperature, the heat of combustion is not found.

Explanation:
Heat of combustion can indeed be measured at room temperature, making this statement incorrect.

21. What is a necessary condition for a reaction to be spontaneous at all temperatures?

A. \( \Delta H < \Delta G \)

B. \( \Delta G \) and \( \Delta H \) should be positive

C. \( \Delta H = \Delta G = 0 \)

D. \( \Delta G \) and \( \Delta H \) should be negative

The correct answer is D. \( \Delta G \) and \( \Delta H \) should be negative.

Explanation:
For spontaneity at all temperatures, both enthalpy and Gibbs free energy should be negative.

22. A gas is compressed to half of its initial volume isothermally. The same gas is then compressed again until the volume is reduced to half through an adiabatic process. Then:

A. Work done during isothermal compression is more

B. Work done is independent of the processes used for compression

C. Work done is more during the adiabatic process

D. Work done depends on the atomicity of the gas

The correct answer is C. Work done is more during the adiabatic process.

Explanation:
In adiabatic compression, all work increases internal energy, making it higher than in isothermal compression.

23. Select the factor that affects the heat of reaction based on Kirchhoff’s equation:

A. Molecularity

B. Temperature

C. Pressure

D. Volume

The correct answer is B. Temperature.

Explanation:
Kirchhoff’s law states that temperature affects the heat of reaction due to changes in heat capacity with temperature.

24. For all reactions, what is the nature of chemical dissociation?

A. Exothermic

B. Reversible

C. Endothermic

D. Reversible and endothermic

The correct answer is D. Reversible and endothermic.

Explanation:
Dissociation reactions typically absorb energy and are reversible, making them endothermic.

25. Which of the following is the largest unit of energy?

A. Electron volt

B. Joule

C. Calorie

D. Erg

The correct answer is C. Calorie.

Explanation:
Among these units, the calorie is the largest, with 1 calorie approximately equal to 4.18 joules.

Thermodynamics

is a foundational concept in physics and engineering, impacting various fields, from chemical processes to mechanical engineering. This article dives into key areas of thermodynamics and highlights the benefits of online MCQ thermodynamics tests that offer convenient learning, instant feedback, and self-assessment. Students, especially those in Class 11 and Class 12, as well as candidates preparing for JEE and NEET, can benefit significantly from these resources. Below, we provide a detailed look at thermodynamic principles, major laws, and types of online thermodynamic tests available.

Core Concepts in Thermodynamics

Thermodynamics explores the relationship between heat, work, and energy. Here’s a breakdown of its main principles:

• The Zeroth Law of Thermodynamics: Establishes the concept of temperature and thermal equilibrium. When two bodies are in thermal equilibrium with a third body, they are also in equilibrium with each other.
• The First Law of Thermodynamics (Law of Energy Conservation): Asserts that energy can neither be created nor destroyed. This law is crucial for understanding energy transfer in thermodynamic systems, often tested through first law of thermodynamics MCQ questions.
• The Second Law of Thermodynamics: Introduces the concept of entropy, explaining why energy spontaneously tends to disperse if not constrained.
• The Third Law of Thermodynamics: States that as the temperature approaches absolute zero, the entropy of a system approaches a constant minimum.
• Heat Transfer: Understanding conduction, convection, and radiation is essential for applying thermodynamic laws. This topic is covered extensively in heat and thermodynamics MCQs with solutions.

Preparing for Thermodynamics Exams

For students aiming to excel in competitive exams, online resources provide a range of tests that strengthen understanding and improve test-taking strategies.

1. Thermodynamic Online Tests: Designed for a thorough understanding of thermodynamic principles, these tests are suitable for Class 11 and Class 12 students to gauge knowledge and identify areas for improvement.
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3. AP Chemistry Thermodynamics MCQs: Useful for students preparing for the AP Chemistry exam, covering key thermodynamic concepts in chemistry.
4. Free Online MCQ Thermodynamics Tests: Many platforms offer free online MCQ thermodynamics tests with both conceptual questions and complex problem-solving exercises.
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6. Thermodynamics PDF Resources: Comprehensive resources like online MCQ thermodynamics tests with answers PDFs are useful for revisiting questions and explanations.

Benefits of Online Thermodynamics Tests

• Flexible Learning: Tests cater to different educational levels and allow students to learn at their own pace.
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In summary, online MCQ tests on thermodynamics are an excellent resource for building a solid understanding of energy principles, laws of thermodynamics, and heat transfer. These tests cater to various educational levels and exam preparations, from JEE and NEET to AP Chemistry. With resources such as thermodynamics MCQ PDFs and mock exams, students are well-prepared to succeed in this fundamental topic.

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