1. Chem 1310: Introduction to physical chemistry Part 3: Equilibria Equilibria and kinetics

2. Kinetics and equilibrium constants If you have an equilibrium then at equilibrium, Rate forward = Rate backward Why would you call this equilibrium?

3. Kinetics and equilibrium constants If we know the rate laws, we can relate them to the equilibrium constant: Rate forward = k 1 [A][B] Rate backward = k -1 [X][Y] Set equal: k 1 [A][B] = k -1 [X][Y]  But, even if rate laws are very complicated the K C expression holds...

4. Steady-state and equilibrium Suppose you have The pure steady-state approximation is

5. Steady-state and equilibrium We often also neglect k 2 relative to k 1 and k -1 : This is called the pre-equilibrium assumption. It is usually OK, but why make it if you don't need to?

6. Kinetics, equilibria, and temperature For rate constants, we usually have k = A e -Ea/RT This means that for a k 1 /k -1 equilibrium, we have So we have a straight line of log K vs 1/T. This is also true for reactions with more complicated rate laws.