Introduction to Catalysis - Online Tutor, Practice Problems & Exam Prep

Catalysts are substances that enhance reaction rates by lowering the activation energy (E_a) without being consumed, while not affecting the equilibrium constant (K_eq). They achieve this by stabilizing the transition state, altering the reaction mechanism to create multiple transition states, or increasing reactant reactivity. This can enhance the nucleophile or electrophile's reactivity and improve the leaving group's ability, often by making it a weaker base. Understanding these mechanisms is crucial for mastering reaction kinetics and catalysis in organic chemistry.

Introduction to Catalysis Concept 1

Hey everyone. So let's take a look at the intro to catalysis. Now recall that catalysts are substances that increase the rate of a reaction without being consumed. We're going to say here that they help to lower the energy of activation, which is ea, without changing the equilibrium constant, which is capital keq. Here, we're going to say that a catalyst can lower the energy of activation in three ways.

The first way is by stabilizing our transition state. Here, just imagine that this blue hill here represents our uncatalyzed reaction and the red one represents our catalyzed reaction. Our y-axis deals with the energy of activation, and our x-axis is time for all three of these graphs. We can see that the red hill is shorter, lower down, which would mean we have a lower energy of activation. This would help to increase the stability of our transition state.

Another way a catalyst can work is it alters the reaction mechanism. Our uncatalyzed reaction is one step since it has one transition state. But now, we have one, two of these transition states, so now it's a two-step process. And then finally here, we can increase our reactant reactivity. So if we take a look here, we have increased our reactive reactant because here we started down over here, and we're going to say now we're over here at a higher energy state.

So we're going to have a reactant that's even more reactive. And we're going to see that it also shifts our reaction a little bit more to the right in terms of time. What is the effect of this? Well, this is going to help to increase the reactivity of our electrophile and or nucleophile within this reaction, and then it also could help to increase the leaving group tendency by making a better leaving group. Typically, this makes it a weaker base which will translate to it being a better leaving group.

So these are the three ways in which catalysts can lower our energy of activation.

Introduction to Catalysis Example 1

In this example question, it says, select the best way in which an acid catalyst can increase the rate of organic reactions. So, a, by shifting the equilibrium towards the products thus resulting in a faster rate. Remember, a catalyst affects the rate of a reaction. Here they're talking about equilibrium. Remember, a catalyst does not affect the equilibrium constant, so it would not affect which way the reaction shifts.

All it can do is help to speed up the reaction. It doesn't control the direction of the reaction. So this doesn't work. By providing a higher energy pathway for the reaction to take, remember we want to go through a lower energy pathway, not a higher one, so this is out. By increasing the concentration of reactants, a catalyst doesn't increase the amount of a reactant or products in terms of our reaction, so this wouldn't work.

By increasing the electrophilicity of a reactant, thus decreasing the energy of activation of the reaction pathway. So this is the best answer out of the ones given. This is one of the ways in which a catalyst can help to decrease the energy of activation for a given reaction. You can do this by increasing the reactivity of an electrophile and or nucleophile within a given reaction. So here, option d is our best answer.