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It states in the book that breaking bonds is always endothermic and requires energy. However in biology, breaking a phosphate group from ATP to form ADP releases energy. Can someone help me understand this?
When the phosphate bond of ATP is broken, a small input of energy is required. However, the formation of new bonds (between OH and the last P in ADP) releases lots of energy so the net energy change is an increase in energy.
Breaking bonds itself is an endothermic process because it requires energy to break any bond. However, whether a reaction is endothermic or exothermic depends on the difference between the energy needed to break bonds and the energy released when new bonds form. When ATP is converted into ADP it the reaction overall releases more energy than it takes to break the bond.
The breaking of bonds always requires energy. However, the overall heat change of the system also takes into account other factors. For instance, the breaking of the bond between two phosphates in the decomposition of ATP into ADP and inorganic phosphate requires an energy input and is therefore endothermic. However, there is a strong repulsion between the two negatively charged phosphate groups that are held together by that bond which results in the release of this potential energy when the bond is broken. Thus, the breaking of the bond, in this case, also releases energy and is exothermic. When looking at the overall reaction, energy is required to break the bond, but it is also released when the bond is broken, and the energy released when the bond is broken is greater than the energy required to break the bond. Therefore, the breaking of the bond is endothermic whereas the overall reaction is exothermic.
In LS we learned that there is an input of energy to overcome the energy barrier, and that energy was released. But the energy put in or released depends on the type of bond that is broken. Determining enthalpy depends on the difference of energy between input to break and output to form these bonds.
Brian_Ho_2B wrote:It states in the book that breaking bonds is always endothermic and requires energy. However in biology, breaking a phosphate group from ATP to form ADP releases energy. Can someone help me understand this?
It is important to understand that the when an reaction is exothermic or exergonic the amount of energy released through the formation of new bonds and intermolecular interactions is larger than the energy needed to break bonds. So yes, the breaking of ATP to ADP and P does require a small amount of energy. However, the intermolecular interactions that the P group makes with other molecules releases more energy than was needed to break the bond. This means that the reaction will overall add enthalpy to the surroundings. I hope that this makes sense!
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