Thermodynamics

Thermodynamics is the accounting system of chemistry: it tells you how much energy a reaction releases or absorbs, and whether the reaction will happen at all. This chapter builds that system from the ground up. It starts with the vocabulary — system and surroundings, open, closed and isolated systems, state functions against path functions — then defines internal energy and states the first law, Delta U = q + w, in the IUPAC sign convention. From there it works out pressure-volume work for irreversible and reversible expansions, introduces enthalpy and the relation Delta H = Delta U + Delta n_g RT, and shows how both quantities are measured by bomb and coffee-cup calorimetry. The thermochemistry that follows — standard enthalpies of formation and combustion, Hess's law, bond, lattice and solution enthalpies — is the part boards and NEET lean on hardest. The chapter then turns to the harder question of direction: why enthalpy alone cannot predict spontaneity, what entropy measures, the second law, and finally Gibbs energy, whose sign settles spontaneity and whose standard value fixes the equilibrium constant through Delta G = -RT ln K.