There are as many applications of free energy as reactions. We can only focus on a small number of these. One important set of reactions in this course will be reactions that occur in living cells. Metabolic reactions occur as series of coupled reactions, which are not in equilibrium. Rather each reaction consumes some products from the previous reaction so that the steady state concentrations of reagents is often far from equilibrium. This is only one example of applications of free energy to a non-equilibrium condition. For example saturated solutions of not in equilibrium. In a saturated solution of a crystalline solid material, we often produce a crystal very rapidly by introducing a seed crystal into the saturated solution. This is shown in the banner figure on this page.
Justification for the free energy function
The free energy function can describe both equilibrium and non-equilibrium processes. In the video below we review the role of the system and the surroundings in defining a single state function that has the power to predict the direction of spontaneous change. The idea of dividing up space into system and surroundings has a particular validity in the study of cell biology. Cells are systems that appear to defy the statement that the entropy of the universe tends towards a maximum. Cells are highly organized, which is indicative of a negative entropy change during their growth and development. This appears to defy the statement that the entropy of the universe tends towards a maximum. The resolution to this apparent conceptual problem lies in the fact that the cell can be considered system and the energy required for cell growth is dissapated as heat in the surroundings. The total entropy change from the cell's growth is postive since the entropy change in the surroundings is positive and outweighs the negative entropy chnage in the system.
