Understanding Gibbs Free Energy

Gibb's Free Energy

What is Gibbs Free Energy?

For a simple definition, Gibbs free energy can be described as

A measure of the amount of energy available to do work.

Gibbs Free Energy is invented by Josiah Willard Gibbs (February 11, 1839 – April 28, 1903) – an American scientist who made important theoretical contributions to physics, chemistry, and mathematics
Gibbs Free Energy is invented by Josiah Willard Gibbs (February 11, 1839 – April 28, 1903) – an American scientist who made important theoretical contributions to physics, chemistry, and mathematics. More on Josiah Willard Gibbs

Gibbs free energy is used in chemistry to help you determine and predict ahead of time whether a chemical process is spontaneous or non-spontaneous.

You might be wondering what’s the advantage of that. There are many applications in life that we need advance knowledge what to expect. For example in the manufacturing of products – if you have no clue which direction your process is going, then you might produce something totally unexpected and waste a lot of resources.

Gibb's-Free-Energy-sponaneous

Spontaneous Process

In a spontaneous process, it happens automatically.

Gibbs free energy non-spontaneous

Non-spontaneous Process

In a non-spontaneous process, energy input is necessary to trigger off a process. You need activation energy.

The Gibb’s Free Energy is simply a method of telling whether a chemical process will take place spontaneously or non-spontaneously.

  • The Gibbs free energy calculates the amount of energy available in a system to do work like carrying out a chemical reaction.
  • Gibbs free energy is only applicable for systems under constant temperature and pressure.
  • The Gibbs calculation allows you to determine whether a process is spontaneous or not.
  • Gibbs calculation uses the relationship between Ethalpy and Entropy in a system to determine the spontaneity of a process.

bread making non-spontaneous process

HOW TO DETERMINE IF A REACTION IS SPONTANEOUS

For notes on spontaneity, please click here >>

Gibbs free energyGibbs Free Energy is the energy associated with a chemical reaction that can be used to do work.

∆H – Enthalpy is the change of heat in a system due to chemical reaction measured in joules

∆S –Entropy is the measure of energy dispersal in j/k

∆G – Gibbs free energy

∆Gsystem = ∆Hsystem – T∆Ssystem

  • If ∆G is negative – spontaneous reaction.
  • If ∆G is positive – non spontaneous reaction.

Equation representing the reaction occurring under standard condition (298K and 1atm)
free-energy-deltaO

Now Gibbs free energy is Enthalpy minus Entropy.

Example Calculation

Go here to see an example of Gibb’s Free Energy calculation for the Haber Process of ammonia manufacturing >> icon-sg50

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