Entropy

  1. Entropy is a measure of the disorder or randomness of a system.
  2. The symbol for entropy is S, and its SI unit is joules per kelvin (J/K).
  3. It quantifies the unavailability of a system's energy to perform useful work.
  4. The Second Law of Thermodynamics states that entropy always increases in a spontaneous process.
  5. ΔS = Q/T, where:
    • ΔS is the change in entropy.
    • Q is the heat exchanged.
    • T is the absolute temperature.
  6. In an isolated system, the total entropy either increases or remains constant.
  7. Reversible processes occur with no change in entropy, while irreversible processes increase entropy.
  8. Entropy explains the direction of natural processes, such as heat flow from hot to cold.
  9. It is a key factor in determining the efficiency of thermodynamic systems.
  10. Entropy changes are significant in chemical reactions, phase changes, and heat engines.

Enthalpy

  1. Enthalpy is the total heat content of a system at constant pressure.
  2. The symbol for enthalpy is H, and its SI unit is joules (J).
  3. It is defined as H = U + PV, where:
    • U is the internal energy.
    • P is the pressure of the system.
    • V is the volume of the system.
  4. Enthalpy changes are used to measure heat transfer during chemical reactions and phase changes.
  5. The change in enthalpy (ΔH) for a process is given by:
    • ΔH = Q at constant pressure.
  6. For exothermic reactions, ΔH is negative, as heat is released.
  7. For endothermic reactions, ΔH is positive, as heat is absorbed.
  8. Enthalpy is a key concept in understanding thermodynamic cycles, such as the Rankine and Brayton cycles.
  9. Enthalpy is used to calculate heat changes in enthalpy of formation and enthalpy of combustion.

Internal Energy

  1. Internal energy is the total energy of a system, including kinetic and potential energy at the molecular level.
  2. The symbol for internal energy is U, and its SI unit is joules (J).
  3. It includes the energy due to molecular motion (kinetic) and interactions (potential).
  4. Internal energy is a state function, meaning it depends only on the state of the system, not the process path.
  5. The change in internal energy (ΔU) is given by the First Law of Thermodynamics:
    • ΔU = Q - W
    • Q is the heat added to the system.
    • W is the work done by the system.
  6. Internal energy is crucial in understanding heat and work interactions in thermodynamic systems.
  7. In an ideal gas, internal energy depends only on temperature.
  8. It is used to describe energy changes in processes such as heating, cooling, and compression.
  9. Internal energy plays a central role in determining the properties of thermodynamic systems.

Applications of Entropy, Enthalpy, and Internal Energy

  1. These concepts are essential in designing and analyzing engines, refrigerators, and power plants.
  2. Entropy helps determine the direction and feasibility of natural processes.
  3. Enthalpy is used to calculate heat changes in chemical reactions and phase transitions.
  4. Internal energy is fundamental in energy conservation and thermodynamic cycles.
  5. These principles are applied in studying the Earth's atmosphere, weather systems, and climate.
  6. They are crucial in chemical engineering, particularly in reaction thermodynamics.
  7. Advanced technologies like fuel cells, heat pumps, and solar panels rely on these thermodynamic concepts.

Category

Questions

  1. What is entropy a measure of?
  2. What is the SI unit of entropy?
  3. Which thermodynamic quantity is represented by "H"?
  4. What is the mathematical expression for enthalpy?
  5. What is internal energy a measure of?
  6. Which quantity remains constant in an isothermal process?
  7. What is the relationship between enthalpy change and heat transfer at constant pressure?
  8. What is the change in entropy for a reversible adiabatic process?
  9. What is the significance of the second law of thermodynamics in terms of entropy?
  10. In which process does internal energy remain unchanged?
  11. What is the expression for change in internal energy for a closed system?
  12. What is the SI unit of enthalpy?
  13. Which law of thermodynamics defines internal energy?
  14. What is the relationship between entropy and temperature in a reversible process?
  15. Which thermodynamic quantity is a state function?
  16. What does a positive entropy change indicate about a system?
  17. In a reversible adiabatic process, what happens to entropy?
  18. What is the physical significance of enthalpy?
  19. What is the term for the energy required to break intermolecular bonds in a substance?
  20. What does the term "enthalpy of fusion" refer to?
  21. How is entropy related to spontaneity of a process?
  22. What is the equation for the first law of thermodynamics in terms of enthalpy?
  23. What does a high value of specific heat capacity indicate about a substance?
  24. Which term describes the energy required to increase the temperature of a system by 1°C?
  25. What is the entropy change for a perfect crystal at absolute zero?
  26. Which quantity describes the energy transfer due to a temperature difference?
  27. What is the relationship between enthalpy and internal energy at constant pressure?
  28. How is entropy change calculated for a phase transition?
  29. Which property determines the direction of heat flow?
  30. In which process is the work done equal to the change in enthalpy?
  31. Which of the following statements about entropy is correct?
  32. What does the first law of thermodynamics establish?
  33. Which thermodynamic potential is used to predict spontaneity at constant pressure and temperature?
  34. What does a negative change in enthalpy indicate?
  35. How is internal energy related to kinetic and potential energy of molecules?