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10.5 Gibbs Free Energy

The change in entropy of the surroundings often plays a dominant role in determining whether the process is spontaneous ( if DS is positive ).

Gibbs Free Energy is a criterion for spontaneity and takes into account the entropy change of the surroundings.

The Gibbs Free Energy Function is defined by the equation,

G = H - TS

For change at constant temperature

DG = DH - T D S

Based on DG reaction behavior can be predicted accurately.

DG negative reaction proceeds spontaneously.

0 reaction is at equilibrium

positive reaction will not proceed at all

Free energy or reaction can be calculated as follows :

DG reaction = DG products - DG reactants

Standard Free Energy

A standard free energy change, given the symbol DG0 applies to a reaction run at 250C and 1 atm pressure with reactions and products in their standard states (that state in which the substance occurs under these conditions).

The standard free energy of formation DG0f is defined as the change in standard free energies when 1 mole of a substance is prepared from its constituent elements.

An element in its standard state at 250C and 1 atm is assigned a standard free energy of zero.

The table lists the standard free energy formation of different compounds.


10.1 Introduction
10.2 First Law of Thermodynamics
10.3 Enthalpy
10.4 Second Law of Thermodynamics
10.5 Gibb's Free Energy
10.6 Absolute Entropies

Chapter 11

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