Sample Thermodynamics Questions and Detailed Answers
FAQs on Thermodynamics Practice Paper for Students
1. What is thermodynamics in simple terms?
Thermodynamics is the branch of physics that studies the relationships between heat, work, and energy in physical systems. It helps describe how energy moves and changes form using key principles known as the laws of thermodynamics.
- Focuses on heat and energy transfer
- Explains key concepts like temperature, entropy, and internal energy
- Forms the foundation for engines, refrigeration, and many natural processes
2. What are the four laws of thermodynamics?
The four laws of thermodynamics govern how energy and heat behave in physical systems.
- Zeroth Law: If two systems are each in thermal equilibrium with a third, they are in thermal equilibrium with each other.
- First Law: Energy cannot be created or destroyed, only converted between forms (law of conservation of energy).
- Second Law: In any spontaneous process, the overall entropy (disorder) of the universe increases.
- Third Law: As temperature approaches absolute zero, the entropy of a perfect crystal approaches zero.
3. State the first law of thermodynamics with an example.
The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or changed in form. For example:
- When you heat water in a kettle, the electrical energy is converted to heat energy, increasing the water's internal energy.
- The total energy remains the same, but changes from electricity to heat.
4. What is entropy and why is it important?
Entropy measures the amount of disorder or randomness in a system. It is important because:
- Entropy helps determine the direction of heat flow and spontaneity of a process.
- The second law of thermodynamics states that entropy of the universe tends to increase.
- High entropy means more disorder and less energy available to do work.
5. What is the difference between an open, closed, and isolated system in thermodynamics?
Thermodynamic systems are classified based on how they exchange matter and energy with the surroundings.
- Open System: Can exchange both energy and matter (e.g., an open cup of tea).
- Closed System: Exchanges energy but not matter (e.g., a sealed bottle).
- Isolated System: Does not exchange energy or matter (e.g., an insulated thermos).
6. What is internal energy in thermodynamics?
Internal energy is the total energy contained within a thermodynamic system due to the random motion and interactions of its particles.
- Includes kinetic energy and potential energy at the molecular level
- Changes in internal energy are closely linked to the first law of thermodynamics
- Represented by symbol U in formulas
7. How do you define enthalpy and what is its significance?
Enthalpy (H) is the total heat content of a system at constant pressure. Its significance is as follows:
- It helps measure heat changes in chemical reactions at constant pressure.
- Expressed as H = U + PV, where U is internal energy, P is pressure, and V is volume.
- Important for understanding energy changes in everyday processes and CBSE board exam calculations.
8. Explain the concept of reversible and irreversible processes in thermodynamics.
Reversible processes occur so slowly that the system stays in equilibrium, while irreversible processes occur rapidly and cause loss of energy as heat or friction.
- Reversible: Processes can be reversed by an infinitesimal change (idealized).
- Irreversible: Real-life processes (e.g., burning, mixing) involve energy loss and increased entropy.
9. What do you mean by spontaneous and non-spontaneous processes?
Spontaneous processes occur naturally under given conditions without external intervention, while non-spontaneous processes need outside energy.
- Spontaneous process: Ice melting at room temperature
- Non-spontaneous process: Water freezing at room temperature requires cooling
- Key terms: Gibbs free energy, entropy, and enthalpy play important roles
10. What is the importance of thermodynamics in daily life?
Thermodynamics plays a crucial role in daily life by helping us understand and manage energy efficiently.
- Heating and cooling (refrigerators, air conditioners)
- Cooking and engines (cars, power plants)
- Natural processes (weather, metabolism)
11. State the second law of thermodynamics in terms of entropy.
The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time.
- Entropy increases in all natural processes
- Energy becomes less available to do useful work
- This law explains why certain processes are irreversible
12. What is a thermodynamic equilibrium?
Thermodynamic equilibrium is a state where a system's properties remain constant over time, with no net flow of energy or matter.
- Includes thermal, mechanical, and chemical equilibrium
- All driving forces for change are balanced
