Understand state functions, Hess's Law, entropy changes, and Gibbs free energy for spontaneity in chemical systems.
Thermodynamics governs energy transformations and spontaneity in physical and chemical processes. It is a cornerstone chapter of Class 11 Physical Chemistry with direct applications across chemical equilibrium and electrochemistry.
First Law of Thermodynamics: Energy can neither be created nor destroyed: Delta U = q + w. For isothermal reversible expansion of an ideal gas: w = -2.303 nRT log (V2 / V1). Enthalpy (H = U + PV) measures heat content at constant pressure.
Hess's Law of Constant Heat Summation states that total enthalpy change during a reaction remains identical whether the reaction takes place in one step or several steps. Thermochemical equations must be balanced with physical state indicators.
Second Law & Gibbs Free Energy (G): Spontaneity depends on Universe Entropy change (Delta S Total > 0). Gibbs-Helmholtz equation: Delta G = Delta H - T Delta S. For spontaneous processes at constant T and P, Delta G must be negative. At equilibrium, Delta G = 0 and Delta G° = -2.303 RT log K. Dr. Aarzoo Saini trains students in Thermodynamic sign conventions at We-Gyaan Classes Roorkee.
Key Takeaways for Students
- Remember First Law equation: Delta U = q + w with IUPAC work sign conventions.
- Apply Hess's Law to calculate formation, combustion, and bond dissociation enthalpies.
- Evaluate spontaneity using Delta G = Delta H - T Delta S.
- Relate standard Gibbs free energy to equilibrium constant using Delta G° = -RT ln K.
Authored by Dr. Aarzoo Saini
Founder & Lead Educator at We-Gyaan Classes Roorkee, with over 20 years of teaching excellence in Science and Chemistry for Board Exams, NEET, JEE, and CUET.