Fundamentals of Thermodynamics
1. Define a thermodynamic system and its surroundings.
Answer: A thermodynamic system is the part of the universe that is being studied, while the surroundings are everything outside the system. The system and surroundings are separated by a boundary, which can be real or imaginary.
2. Differentiate between extensive and intensive properties with examples.
Answer: Extensive properties depend on the amount of matter in a system (e.g., mass, volume, total energy), while intensive properties do not depend on the amount of matter (e.g., temperature, pressure, density).
3. What is a state function? Give two examples.
Answer: A state function is a property that depends only on the current state of the system, not on how it got there. Examples include enthalpy (H) and internal energy (U).
4. Describe an isothermal process.
Answer: An isothermal process is one that occurs at a constant temperature. In such a process, the internal energy of an ideal gas remains constant.
5. Explain the difference between an adiabatic process and an isochoric process.
Answer: An adiabatic process occurs without any heat exchange between the system and its surroundings, while an isochoric process occurs at a constant volume, meaning no work is done by the system.
The First Law of Thermodynamics
6. State the first law of thermodynamics.
Answer: The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or transformed. Mathematically, it is expressed as ΔU = Q – W, where ΔU is the change in internal energy, Q is heat added to the system, and W is work done by the system.
7. Define internal energy and enthalpy. How are they related?
Answer: Internal energy (U) is the total energy contained within a system, including kinetic and potential energy at the molecular level. Enthalpy (H) is the total heat content of a system, defined as H = U + PV, where P is pressure and V is volume. Enthalpy accounts for internal energy and the work done to displace the surroundings.
8. What is heat capacity? How is it different from specific heat capacity?
Answer: Heat capacity (C) is the amount of heat required to raise the temperature of a system by 1 degree Celsius. Specific heat capacity (c) is the heat capacity per unit mass of a substance. Molar heat capacity is the heat capacity per mole of a substance.
9. State Hess’s law of constant heat summation.
Answer: Hess’s law states that the total enthalpy change for a reaction is the same, regardless of the number of steps in which the reaction occurs. It is based on the principle that enthalpy is a state function.
10. What is the enthalpy of formation?
Answer: The enthalpy of formation (ΔH_f^0) is the change in enthalpy when one mole of a compound is formed from its elements in their standard states under standard conditions (298 K and 1 atm).
Enthalpies of Various Processes
11. Define the enthalpy of combustion.
Answer: The enthalpy of combustion (ΔH_c^0) is the change in enthalpy when one mole of a substance is completely burned in oxygen under standard conditions.
12. What is the enthalpy of atomization?
Answer: The enthalpy of atomization (ΔH_a) is the change in enthalpy when one mole of a compound is completely dissociated into its atoms in the gas phase.
13. Explain the enthalpy of sublimation.
Answer: The enthalpy of sublimation (ΔH_sub) is the change in enthalpy when one mole of a solid substance converts directly into gas without passing through the liquid phase.
14. Describe the enthalpy of hydration.
Answer: The enthalpy of hydration (ΔH_hyd) is the change in enthalpy when one mole of gaseous ions is dissolved in water to form an aqueous solution.
15. What is the enthalpy of ionization?
Answer: The enthalpy of ionization (ΔH_ion) is the change in enthalpy when one mole of electrons is removed from one mole of gaseous atoms or ions.
The Second Law of Thermodynamics
16. State the second law of thermodynamics.
Answer: The second law of thermodynamics states that the total entropy of an isolated system always increases over time, and processes occur in a direction that increases the overall entropy of the universe.
17. What is the significance of entropy (S) in spontaneous processes?
Answer: Entropy is a measure of the disorder or randomness of a system. For a process to be spontaneous, the total entropy change of the system and surroundings (ΔS_universe) must be positive.
18. Define Gibbs free energy (G).
Answer: Gibbs free energy (G) is a thermodynamic potential that measures the maximum reversible work a system can perform at constant temperature and pressure. It is given by G = H – TS, where H is enthalpy, T is temperature, and S is entropy.
19. What is the criterion for spontaneity in terms of Gibbs free energy?
Answer: A process is spontaneous if the change in Gibbs free energy (ΔG) is negative (ΔG < 0) under constant temperature and pressure.
20. How is the equilibrium constant (K) related to the standard Gibbs free energy change (ΔG°)?
Answer: The equilibrium constant (K) is related to the standard Gibbs free energy change (ΔG°) by the equation ΔG° = -RT ln(K), where R is the gas constant and T is the temperature in Kelvin.