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 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. Well, there are many applications in life that advance knowledge of the direction the process takes is critical. For example in the manufacturing of products – if you are unable to predict which direction your process is going, then you might be wasting a lot of resources producing unwanted products.

Spontaneous Process


In a spontaneous process, it happens automatically. You might have to start off the process with a little activation energy and the rest will take care of itself. A good example of a spontaneous process is combustion – the burning of substances to produce heat and energy. You may have to light the substance first (giving it activation energy) but once the substance burns, it continues by itself.

Non-spontaneous Process

In a non-spontaneous process, a continuous energy input is necessary for the reaction to proceed in a certain direction.

A good example is photosynthesis, a process in which plants use to make glucose. Photosynthesis requires energy in the form of sunlight to drive chemical reactions. Therefore at night when it’s dark, photosynthesis does not work.

Spontaneous vs Non-spontaneous process

Gibb's-Free-Energy-sponaneous Gibbs free energy non-spontaneous
A spontaneous process – no continuous energy input from external source is necessary to run the process A non-spontaneous process – a continuous energy input is necessary to run the process

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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