Enthalpy, Entropy & Gibbs Free Energy

Gibb's 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 and is determined 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.  Entropy can be thought of as the degree to which energy is dispersed throughout a system. For example, water has a greater entropy than ice because energy is more spread out in water than in ice. 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.
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

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