Create a free Team What is Teams? Learn more. What is the relation between chemical thermodynamics and chemical kinetics? Asked 5 years, 9 months ago. Active 5 years, 9 months ago. Viewed 1k times. Improve this question. Add a comment. Active Oldest Votes. Improve this answer. Aaditya Joshi Aaditya Joshi 5 5 bronze badges.
Knowledge of either yields nothing of the other right? Why is that? If you look at developement of thermodynamics it was developed for handling energy in form of heat. Thermodynamics deals with macroscopic systems. So it doesn't tell about rates. The position of equilibrium is where both the reactants and products are present and the concentrations of all species involved stays without changing over time, and it is specific for a particular reaction when the reaction is done under standard conditions.
Thermodynamics may predict that a reaction will definitely take place because the energy of the products is less than that of the reactants. However, in practice, one may need the principle of kinetics to make the reaction happen at an appreciable rate. Kinetics is more often involved in the field of chemical sciences.
Hence it relates as to how fast a chemical reaction might occur or how fast the chemical equilibrium point is reached. Various parameters are associated with the control of the rates of chemical reactions. The molecules involved must collide with sufficient energy and in the proper orientation. Any condition that meets this requirement increases the rate of a chemical reaction.
And the same on the right side, just again extending between the start and endpoints of our reactions. So I'll go ahead and indicate that this green line in both cases refers to our delta G values. And in a different color, let's say red, I'm going to go ahead and indicate the activation energy, which takes into account the change in energy between the high-energy intermediate and the reactants.
So in the case on the left, that change is indicated here with red. And on the right side, the change between the intermediate and the reactant is a bit longer, so we'll go ahead and indicate that here. Now, activation energy is an important quantity to take into account, because in order for molecules to react, they must have enough energy to overcome this activation energy barrier. Essentially, in the case of a spontaneous reaction for example, I think of it like the energy one needs to get a ball to start rolling down a hill.
We all know that gravity will make a ball roll down a hill, which is like a negative delta G value, it's telling us that the reaction is very thermodynamically favorable. But we need to sometimes give the ball push in order for the reaction to occur.
And so that's kind of this little help that it needs to go over before it can actually proceed. For a non-spontaneous reaction, the idea is essentially the same. We still need to have some activation energy. But in addition, because it requires an input of energy, we can think about it as rolling ball up a hill instead of down a hill. Now in general, the idea is that the lower this free energy change, the faster a reaction will occur. And remember I'm saying faster, so I'm talking about kinetics.
I'm talking about the rate of a reaction. So just to write that out, the activation energy, the smaller it is, the faster the reaction will proceed.
Now in biochemistry in particular, it's really important to distinguish between these two terms of thermodynamics and kinetics, which we've drawn out in our diagrams as the change in delta G over the change in activation energy. Because many biochemical reactions in our body are kinetically unfavorable, that is to say they have a very high energy of activation even if they are thermodynamically favorable. This is why our bodies have enzymes, which essentially lower the activation energy of a reaction.
So I went ahead and drew a dotted white line that's a little bit lower, so you can see that when an enzyme is present, the height of the barrier has decreased. And if it's decreased, the reaction will proceed faster. Now, there's one analogy that my chemistry professor used to tell us all the time that really helped me understand the interplay between kinetics and thermodynamics as they apply to whether or not a reaction will occur.
So I'm going to go ahead and scroll down so we can briefly talk about this analogy, which is I think a fun way to think about all of this. So let's say you went to a dating website, because you were looking for your perfect match.
And this dating website told you that your perfect match lived halfway across the globe. And this is such a perfect match, and they have all these algorithms.
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