IIT JEE Ch. 6 ENERGETICS Core Points for Revision

JEE Syllabus

Energetics:
First law of thermodynamics;
Internal energy, work and heat,
pressure-volume work;
Enthalpy,
Hess's law;
Heat of reaction, fusion and vapourization;
Second law of thermodynamics;
Entropy;
Free energy;
Criterion of spontaneity.
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First law of thermodynamics;

Energy cannot be created or destroyed.

U = q + w

Internal energy of matter is equal to kinetic energy and potential energy.

The change in internal energy is equal to heat transferred and work done between the system and the surroundings.

Pressure volume work: If the pressure is constant and the matter expands, the work done is given by p * change in volume. This in termed as pressure volume work.

Enthalpy = U + pv

Hess's Law

Hess's Law states that the enthalpy change for a reaction that occurs in many steps is the same as if it occurred in one step. Another way to put this is if several reactions add up to some total reaction, then their enthalpy changes will add up to the enthalpy change for the total reaction.


Second law of thermodynamics

In general it is impossible to perform a transformation whose only final result is to convert into useful work heat extracted from a source that is at the same temperature throughout. This statement is Lord Kelvin's version of the second law of thermodynamics. Another version of this law, formulated by R. J. E. Clausius, states that a transformation is impossible whose only final result is to transfer heat from a body at a given temperature to a body at higher temperature; in other words, the spontaneous flow of heat from hot to cold bodies is reversible only with the expenditure of mechanical or other nonthermal energy.

The Second law of Thermodynamics states that every spontaneous change is accompanied by an increase in entropy which is a measure of the randomness or disorder of a system.