Why is ATP hydrolysis an exergonic reaction?
1. The entropy, which is the level of disorder, of ADP is greater than that of ATP. Therefore, due to thermodynamics, the reaction spontaneously occurs because it wants to be at a higher entropy level. Also, the Gibbs’ free energy of ATP is higher than that of ADP. Naturally, molecules want to be at a lower energy state, so equilibrium is shifted towards ADP. 2. Electrostatic repulsion of the four negative charges on the oxygens of the ATP molecule. Naturally, like charges repel and opposite charges attract. Therefore, if there are four negative charges in close proximity to one another, they will naturally repel each other. This makes ATP a relatively unstable molecule because it will want to give away its phosphate groups, when given the chance, in order to become a more stable molecule. 3. Resonance stabilization of ADP and of Pi is greater than that of ATP. The oxygen molecules of the ADP are sharing electrons. Those electrons are constantly being passed back and forth between the
