IIT JEE Chemistry Practice Paper – Part 16 (Thermodynamics) with Formula Sheet

IIT JEE Chemistry – Thermodynamics Summary & Formula Sheet

Thermodynamics is the branch of physical chemistry that studies energy changes accompanying physical and chemical processes. It helps us understand the direction and feasibility of reactions — an essential part of IIT JEE Chemistry.

1. Basic Terms

• System: The part of the universe under study (e.g., reacting mixture).
• Surroundings: Everything outside the system.
• Types of Systems:
  • Open – exchanges both matter and energy.
  • Closed – exchanges energy but not matter.
  • Isolated – exchanges neither energy nor matter.

2. Thermodynamic Processes

• Isothermal: Temperature constant (ΔT = 0).
• Adiabatic: No heat exchange (q = 0).
• Isobaric: Constant pressure.
• Isochoric: Constant volume.
• Reversible: Infinitely slow, equilibrium maintained.
• Irreversible: Rapid and spontaneous, not in equilibrium.

3. First Law of Thermodynamics

Energy can neither be created nor destroyed; it can only be transformed.

ΔU = q + w

• ΔU – Change in internal energy
• q – Heat absorbed by the system
• w – Work done on the system

For ideal gas: w = –P_extΔV

At constant volume: q_v = ΔU
At constant pressure: q_p = ΔH

4. Enthalpy (H)

H = U + PV

Change in enthalpy: ΔH = ΔU + PΔV

For chemical reactions:
ΔH = ΣH_products – ΣH_reactants

• Exothermic: ΔH < 0
• Endothermic: ΔH > 0

5. Heat Capacities

C_p – C_v = R

For n moles of gas:
ΔU = nC_vΔT    and    ΔH = nC_pΔT

6. Hess’s Law

The total enthalpy change of a reaction is the same, irrespective of the path taken.

ΔH_overall = ΣΔH_{individual steps}

7. Second Law of Thermodynamics

The entropy (S) of an isolated system always increases in a spontaneous process.

ΔS_universe = ΔS_system + ΔS_surroundings > 0

8. Gibbs Free Energy (G)

G = H – TS

Change in Gibbs energy: ΔG = ΔH – TΔS

• ΔG < 0 → Reaction is spontaneous
• ΔG = 0 → System at equilibrium
• ΔG > 0 → Non-spontaneous reaction

9. Key Relations

• ΔG° = –RT ln K (Relation between Gibbs energy and equilibrium constant)
• w = –nRT ln(V₂/V₁) (Reversible isothermal expansion of ideal gas)

Conclusion

Thermodynamics forms the backbone of physical chemistry, connecting energy, heat, and work with the spontaneity and equilibrium of reactions. By mastering concepts like internal energy (U), enthalpy (H), entropy (S), and Gibbs free energy (G), IIT JEE aspirants can predict the feasibility and direction of any chemical process — making it one of the most scoring topics in the exam.