Thermodynamics (Chemical Perspective) – Multiple Choice Questions (MCQs)

1. 25. What is activity (ai)?

   • A. A measure of the effective concentration of a substance in a solution
   • B. A measure of temperature
   • C. A measure of pressure
   • D. A measure of volume

2. 26. What is the activity coefficient (γi)?

   • A. A correction factor that relates activity to mole fraction or concentration for real solutions
   • B. A constant value for all solutions
   • C. A measure of temperature dependence
   • D. A measure of pressure dependence

3. 27. What is Raoult's Law?

   • A. P_i = x_i * P_i^*
   • B. P_i = k * x_i
   • C. P_total = ΣP_i
   • D. P_i = P_total * y_i

4. 28. What is Henry's Law?

   • A. P_i = x_i * P_i^*
   • B. P_i = k * x_i
   • C. P_total = ΣP_i
   • D. P_i = P_total * y_i

5. 29. What is the triple point on a phase diagram?

   • A. The point where all three phases (solid
   • B. liquid
   • C. gas) coexist in equilibrium
   • D. The point where two phases coexist

6. 30. What is the critical point on a phase diagram?

   • A. The point where all three phases coexist
   • B. The temperature and pressure at which the liquid and gas phases of a substance merge into a single fluid phase
   • C. The melting point
   • D. The sublimation point

7. 31. What is an azeotrope?

   • A. A mixture of two or more liquids whose proportions cannot be changed by simple distillation
   • B. A pure substance
   • C. A solid-liquid mixture
   • D. A gas-liquid mixture that can be separated by distillation

8. 32. What is the lever rule used for in phase diagrams?

   • A. To determine the relative amounts of each phase present in a two-phase region
   • B. To determine the boiling point of a mixture
   • C. To determine the critical temperature
   • D. To determine the pressure of a system

9. 33. What is the concept of excess properties in thermodynamics?

   • A. The difference between the actual thermodynamic property of a mixture and the property calculated assuming ideal behavior
   • B. Properties that are always positive
   • C. Properties that are always negative
   • D. Properties that are only relevant for pure substances

10. 34. What is the standard state for a pure solid or liquid?

    • A. The pure substance at 1 bar (or 1 atm) and a specified temperature
    • B. The substance in solution
    • C. The substance as a gas
    • D. The substance at its critical point

11. 35. What is the standard state for a pure gas?

    • A. The pure gas behaving ideally at 1 bar (or 1 atm) and a specified temperature
    • B. The gas as a liquid
    • C. The gas at its dew point
    • D. The gas at its critical point

12. 36. What is the standard state for a component in a solution?

    • A. A hypothetical ideal solution of unit molality or molarity at 1 bar and a specified temperature
    • B. The pure component at 1 bar and specified temperature
    • C. The component as a gas
    • D. The component as a solid