Enthalpy, Entropy & Gibbs Free Energy

 Enthalpy  Entropy Gibbs Free Energy
 icon-enthalpy  icon-entropy
Enthalpy is the amount of heat energy transferred (heat absorbed or emitted) in a chemical process under constant pressure. Entropy measures the amount of heat dispersed or transferred during a chemical process. Gibbs Energy is also known as energy available to initiate a chemical process under constant pressure and temperature.
It is expressed as a change in enthalpy (ΔH) because the total enthalpy (H) of a system cannot be measured directly.  Nature tends to form chaos than order — aging, decaying, rusting, etc. Usable energy is transformed to unusable energy when work is performed. Entropy is often described as a measure of randomness but this mustn’t be confused with random patterns or arrangements.Entropy is about heat. The change in entropy is expressed as ∆S.  The higher energy dispersal means higher entropy. Some reactions are spontaneous (eg. rusting). A spontaneous process happens by itself without any energy added to the system (apart from the activation energy). A non-spontaneous process will not take place unless it is driven by an external source of energy.

∆G = ∆H — T•∆S

∆G = Gibbs Free Energy

∆H = Change in Enthalpy

T = Temperature in K

∆S = Change in Entropy

ΔH < 0 ∆S > 0 ∆G < 0
• Total energy of products lower than total energy of reactants.

• The process is exothermic.

• Gives off heat.

Entropy increases. Process is spontaneous

4 thoughts on “Enthalpy, Entropy & Gibbs Free Energy

  1. The relation [dS <0] looks like a typo. I think it should be [dG <0], neatly fitting beneath the explanation for Gibbs' Energy :).

  2. I believe there is a typo……

    In an exothermic reaction Total energy of products is lower than total energy of reactants..the natural flow is energy minimisation…..hence the delta is negative

    With Positive change in H the process is endothermic…absorbs (latent) heat…..

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