THERMODYNAMICS

CLASS 11 CHEMISTRY – CHAPTER 6

THERMODYNAMICS

1. Define thermodynamics.

Thermodynamics is the branch of chemistry that deals with the study of energy changes involved in physical and chemical processes.

2. What is a system and surroundings?

• System: The part of the universe under study.

• Surroundings: Everything outside the system.

3. What are the types of systems?

1. Open system: Exchange of matter and energy.

2. Closed system: Exchange of energy but not matter.

3. Isolated system: No exchange of matter or energy.

4. What is an extensive property? Give examples.

Properties that depend on the amount of substance.
Examples: Mass, volume, heat capacity, internal energy.

5. What is an intensive property? Give examples.

Properties that do not depend on the amount of substance.
Examples: Temperature, pressure, density, concentration.

6. State the first law of thermodynamics.

Energy can neither be created nor destroyed, but can be converted from one form to another.
ΔU = q + w
where
ΔU = change in internal energy
q = heat
w = work

7. What is internal energy?

Internal energy is the total energy of all molecules in a system, including kinetic and potential energies.

8. What is enthalpy (H)?

Enthalpy is the heat content of a system at constant pressure.
H = U + PV

9. What is enthalpy change (ΔH)?

The amount of heat absorbed or released during a process at constant pressure.
ΔH = ΔU + PΔV

10. Distinguish between exothermic and endothermic reactions.

• Exothermic: Heat is released, ΔH is negative.
  Example: Combustion.

• Endothermic: Heat is absorbed, ΔH is positive.
  Example: Photosynthesis.

11. Define heat capacity.

Heat capacity is the amount of heat required to raise the temperature of a substance by 1°C or 1 K.

12. Define molar heat capacity.

Heat required to raise the temperature of one mole of a substance by 1°C or 1 K.

13. What is specific heat?

Heat required to raise the temperature of 1 gram of a substance by 1°C or 1 K.

14. State Hess’s Law.

The total enthalpy change in a reaction is the same whether the reaction occurs in one step or multiple steps.

15. What is lattice enthalpy?

Lattice enthalpy is the energy required to separate one mole of an ionic solid into gaseous ions.

16. What is bond enthalpy?

Bond enthalpy is the amount of energy needed to break one mole of bonds in gaseous molecules.

17. Define spontaneity.

A spontaneous process occurs by itself under given conditions without external work.

18. What is entropy (S)?

Entropy is a measure of disorder or randomness of a system.
Greater disorder → higher entropy.

19. What is Gibbs free energy (G)? Write the formula.

Gibbs free energy tells whether a process is spontaneous.
G = H – TS

20. What is the condition for spontaneity in terms of Gibbs free energy?

• ΔG < 0 → Spontaneous

• ΔG > 0 → Non-spontaneous

• ΔG = 0 → Equilibrium

21. Write the relation between ΔG, ΔH and ΔS.

ΔG = ΔH – TΔS

22. Define isothermal and adiabatic processes.

• Isothermal: Temperature remains constant (ΔT = 0).

• Adiabatic: No heat exchange with surroundings (q = 0).

23. What is work of expansion?

When a gas expands against external pressure, it performs work.
w = – P_ext ΔV

24. Define standard enthalpy of formation.

It is the enthalpy change when one mole of a compound is formed from its elements in their standard states.

25. What is standard enthalpy of combustion?

Enthalpy change when one mole of a substance is completely burned in excess oxygen.