Free Energy Equilibrium and Work 17.8-17.9 Presentation

17.8 Free energy and Equilibrium

17.8 Free energy and equilibrium Equilibrium occurs at the lowest value of free energy available to the reaction This is because at this point, no more driving force exists to favor a change in one direction versus another Any system can achieve the lowest possible free energy state by going to equilibrium and NOT TO COMPLETION. This is because at equilibrium, the system stops short of completion and so it never fully forms product to point of stopping

3 cases for free energy at Equilibrium Case #1—DG = 0 Indicates to us that the free energy of the reactants and products are equal when every component is in its standard state System is at equilibrium K = 1, and we also know that pressure = 1 atm

Case #2 DG < 0 In this case DGo is negative (DGproducts – DGreactants) This means that the standard free energy of the products, is less than the standard free energy of the reactants System is NOT at equilibrium Since the products have less free energy, the system must shift equilibrium to them (right) to reach equilibrium K is greater than 1 now because of the shift right Pressure of the products is greater than 1 atm at equilibrium Pressure of the reactants is less than 1 atm at equilibrium

Case #3 DG > 0 In this case DGo is positive (DGoproducts – DGoreactants) System is not at equilibrium System will have to shift equilibrium to the left (favor reactants) to reach equilibrium The reactants have lower free energy The value of K will be less than 1 At Equilibrium the pressure of the products will be greater than 1 At Equilibrium the ressure of the reactants will be less than 1

What does all of this mean? Positive DGo value tells me that the equilibrium will have to shift to the left to reach equilibrium Negative DGo value tells me that the equilibrium will have to shift to the right to reach equilibrium A DGo of 0, means that the system is at equilibrium

17.9 Free Energy and work We need to know if a process is spontaneous or non-spontaneous We also need to know when to apply a catalyst, or when to just give up if a process is not going happen DG essentially tells us the maximum possible amount of useful work that we can obtain from a process If a process is spontaneous, we have free energy availible to do work, and if it’s non-spontaneous we can calculate the minimum amount of energy necessary to make it happen (if possible) DG also allows us to determine efficiency as well In all processes it is important to note that we never obtain the maximum amount of work from any process