Free Energy

Free energy denoted by the letter G is a thermodynamic quantity, with which we can predict the spontaneity of a reaction. The change in free energy (Î”G) is related to the changes in enthalpy and entropy, and temperature as indicated by the equation:

 Î”G = Î”H â€“ TÎ”S
Here, Î”G represents the change in free energy, H represents the change in enthalpy, Î”S represents the change in entropy, and T represents the temperature.

How Can We Predict Spontaneity?

On the basis of free energy change we can predict the spontaneity of a reaction. You should be able to manipulate the above mentioned equation, and once you have found the free energy change, you can do the prediction using the following guidelines.

If Î”G is positive, the reaction generally is nonspontaneous. If Î”G is negative, then the reaction is generally spontaneous. The changes in free energy and spontaneity depend on the change in enthalpy as well as the change in entropy. Besides these two important factors, the temperature at which the reaction takes place also plays a major role in dictating the spontaneity of reactions. Take a look at Table 10-1.