Entropy and Second Law of Thermodynamics - AP Physics 2

1. What is the significance of $\Omega$ in Boltzmann's equation?

   Number of microstates. Represents the total number of possible microscopic arrangements.

2. What does the Second Law imply about perpetual motion machines?

   They are impossible. Entropy increase prevents 100% efficient energy conversion.

3. What does a negative entropy change indicate?

   Decreased disorder or energy dispersal. Negative $\Delta S$ means the system becomes more ordered.

4. Define entropy.

   Entropy is a measure of a system's disorder. Entropy quantifies the randomness or energy dispersal in a system.

5. State the sign of entropy change for a spontaneous reaction.

   Positive. Spontaneous processes always increase total system entropy.

6. What is the significance of the Third Law for entropy?

   Entropy becomes constant at absolute zero. All substances reach minimum entropy at absolute zero temperature.

7. What is the formula for change in entropy?

   $\Delta S = \frac{Q}{T}$. Heat $Q$ divided by temperature $T$ gives entropy change.

8. What is the statistical interpretation of entropy?

   Entropy relates to the number of microstates. More microstates correspond to higher entropy values.

9. In which type of process does total entropy change equal zero?

   Reversible process. Only reversible processes maintain constant total entropy.

10. What is the Second Law of Thermodynamics?

    Entropy of an isolated system never decreases. This fundamental law states entropy never decreases in isolated systems.

11. What is the relationship between entropy and temperature?

    Entropy increases with temperature. Higher temperatures allow more molecular motion and disorder.

12. What is the effect of entropy on energy dispersal?

    Higher entropy means greater energy dispersal. Energy spreads out more uniformly with increasing entropy.

13. Calculate the entropy change for $Q = 150 \, J$ and $T = 75 \, K$.

    $\Delta S = 2 \, J/K$. Using $\Delta S = Q/T = 150/75 = 2$ J/K.

14. What is the entropy change for an isothermal process?

    $\Delta S = \frac{Q}{T}$. For constant temperature, entropy change equals $Q/T$.

15. Which principle dictates that entropy never decreases?

    Second Law of Thermodynamics. This law mandates entropy never decreases in isolated systems.

16. Calculate entropy change for $Q = 500 \, J$ and $T = 300 \, K$.

    $\Delta S = 1.67 \, J/K$. Using $\Delta S = Q/T = 500/300 = 1.67$ J/K.

17. Which physical law relates to energy's ability to do work?

    Second Law of Thermodynamics. Entropy increase limits the conversion of heat to work.

18. What does a decrease in entropy mean for a system?

    The system becomes more ordered. Negative $\Delta S$ indicates reduced randomness and fewer microstates.

19. What is the relationship between entropy and heat exchange?

    Entropy change is proportional to heat exchange. More heat transfer at lower temperatures increases entropy more.

20. How does entropy impact heat engine efficiency?

    Higher entropy reduces efficiency. Rising entropy means less available energy for useful work.

21. How does entropy affect the feasibility of chemical reactions?

    Reactions tend to increase total entropy. Reactions favored when they increase overall system entropy.

22. How does entropy change in irreversible processes?

    Entropy increases. All real processes are irreversible, so entropy always increases.

23. What is the Third Law of Thermodynamics?

    Entropy approaches zero as temperature approaches absolute zero. Perfect crystals reach minimum entropy at 0 K.

24. What happens to entropy in an isolated system over time?

    Entropy increases or remains constant. Second Law prevents entropy decrease in isolated systems.

25. Identify the symbol for entropy.

    S. Standard symbol used to represent entropy in thermodynamic equations.

26. Define a microstate in statistical mechanics.

    A specific configuration of a system's particles. One possible arrangement of all particles in the system.

27. What does a positive change in entropy indicate?

    Increased disorder in the system. Positive $\Delta S$ means more microstates and greater randomness.

28. What does $k$ represent in Boltzmann's formula?

    Boltzmann's constant. Fundamental physical constant linking microscopic and macroscopic properties.

29. Find the entropy change for $Q = 100 \, J$ and $T = 25 \, K$.

    $\Delta S = 4 \, J/K$. Using $\Delta S = Q/T = 100/25 = 4$ J/K.

30. State the units of entropy in the SI system.

    Joules per Kelvin (J/K). Energy per temperature unit in the International System of Units.

31. State the equation for entropy change during phase transition.

    $\Delta S = \frac{\Delta H}{T}$. Enthalpy change divided by temperature during phase changes.

32. Describe the entropy of a perfect crystal at absolute zero.

    Entropy is zero. Perfect order at absolute zero means minimum possible entropy.

33. Define the term 'macrostate'.

    A set of conditions defining a system's state. Observable properties like temperature and pressure define macrostates.

34. What is the entropy change for an adiabatic process?

    $\Delta S = 0$. No heat transfer means no entropy change in ideal case.

35. What does entropy measure in a thermodynamic system?

    Disorder or randomness. Quantifies the degree of molecular chaos or energy spread.

36. Which law applies to the direction of spontaneous processes?

    Second Law of Thermodynamics. Entropy increase determines which processes occur naturally.

37. What is the condition for a process to be reversible?

    Total entropy change is zero. No net entropy increase means the process is reversible.

38. State Boltzmann's entropy formula.

    $S = k \ln \Omega$. Relates entropy $S$ to number of microstates $\Omega$.

39. What is the role of entropy in the heat death of the universe?

    Entropy maximizes, leading to uniform energy distribution. Maximum entropy means complete thermal equilibrium throughout the universe.

40. What is the typical outcome for entropy when mixing gases?

    Entropy increases. Mixing creates more possible molecular arrangements and disorder.

Study these flashcards