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Gibbs Free Energy Equation

If you know that a reaction will proceed as written, then you know which chemicals are reactants and which are products. One way of finding out if your reaction equation is correctly written is to perform the reaction, identifying and measuring reactant and product amounts along the way. That could be impractical for you!

Another way is to get out a pencil and some paper! Finding a negative change in enthalpy (ΔH), i.e. the reaction is exothermic, could direct you to your answer. However, ΔH is not the only factor in determining whether or not a reaction will occur spontaneously; you must also have a net positive change in entropy ( + ΔS ), or randomness.

The combination of ΔH and of ΔS at a constant temperature (K) will allow you to calculate Gibbs energy change (ΔG); think of ΔG as the 'push' for your reaction.

Traditionally Gibbs energy has been called Gibbs free energy , but as IUPAC recommends the term 'Gibbs energy', that is what we will use.