[Music] hi it's Mr Anderson and welcome to my podcast on Gibbs free energy whenever I get to Gibbs free energy in the year I can see my kids eyes gloss over and they're confused and even William Gibbs talks about this in this quote he said the idea of entropy and the second law of Thermodynamics will seem far-fetched and may repel beginners as obscure and difficult for comprehension so what does that mean I'm going to try to tackle something that's been a problem for years I'm going to try to make Gibbs free energy more understandable um and so that you that you really know what it is and understand the power of it especially in biology and so I think the first place to start is the name itself the idea of free kinds of gets in the way and so what I'd like to go back to is the old name which used to be called available energy and so let's think of Delta G as available energy or energy that we can actually use to do work the other thing that I think makes it hard is the the equation itself is confusing we've got Delta G we've got enthalpy we've got entropy we've got words that you're maybe not understanding and so what I'm going to try to do is pair this down to the easiest uh explanation that I can and then we can get into the more of the specifics a little bit later and so the best place to start when you're trying to understand available energy or free energy is to look at spontaneous reactions spontaneous reactions are reactions that once you give them a little bit of a push they'll actually go on their own um these these reactions also will tend to release energy uh and they give energy uh to their surroundings uh quintessential example in life is cellular respiration but let's kind of let's not get there yet so the three reactions that I'm going to talk about here are number one a ball rolling down a slide number two diffusion and then number three a cherry bomb that's exploding and so we're going to apply Gibbs free energy to each of these so let's start with a ball at the top of a slide uh and the ball at the top of the slide is going to roll down to the bottom and so the first thing that I want to give you is uh what's called enthalpy or total energy of a system and so if we say this is a system what happens to the total energy of the system as the ball rolls down the slide well if you know anything about potential energy the amount of potential energy that we have up here is going to be greater than the amount of potential energy that we have down here and so the total en of the system we'll call that H or enthalpy the total energy of the system has gone from a big H to a little H in other words the total energy of the system has decreased when the ball rolls down now if I had to push it up again then we would add energy to the system but this is a spontaneous reaction and the en enthalpy or the total energy is decreasing now in biology we don't move around because of uh potential energy your mechanical potential energy in biology our energy or our potential energy is actually in these Bonds in other words there's a huge amount of potential energy in this bond between the carbon and the hydrogen and so this right here is glucose and if we can release some of that energy we can do it to do work and so again what is h h stands for the total energy of the system and it looks like in a spontaneous reaction that's actually going to get smaller or decrease okay next one let's talk about diffusion so in diffusion imagine that right here we've got a bunch of molecules in this container and they're bouncing around and I remove this wall so if I remove that wall what's going to happen to the molecules the molecules are going to spread out to fill that area we call that diffusion now entropy is uh We call we use the symbol S for that entropy is a measure of the disorder of a system or sometimes we call that the randomness of the system and so let's compare this right here we've got a bunch of molecules on this side and then we got a lot of space over here so what happens to the disorder of that system as I do diffusion well it's becoming more disordered in other words the entropy is increasing what's an example of that let's say I go into your room and your room's a mess it looks like this if I say clean up your room then you could go like that and so what happens through diffusion or in this spontaneous reaction well let's say remove this wall what's going to happen now now we're going to get even more Disorder so we're going to even get a bigger S value and so in this spontaneous reaction it looks like the S value is increasing okay last one is that cherry bomb so let's say we have a cherry bomb we put it on the desk does it explode no and one of the reasons it doesn't is the temperature is really low and so let's say I add a bonfire to the situation so I increase the temperature does that make it a more spontaneous reaction or is the reaction more likely to happen happen or less well it's more likely to happen if I increase the temperature more likely to get an explosion okay so those three things total energy or enthalpy entropy or S and temperature can affect uh spontaneous reactions so now let's apply that to Gibbs free energy and so uh before we actually get to the equation let's just do a little algebra here so let's say I wrote this equation x = y - A B okay so let's say we had this equation right here and I were to decrease this value the Y value what would that do to the XV value it would decrease it right let's say I were to increase the a value and increase the B value what would that do to the x value well since we're subtracting right here that would decrease it as well or make it even go farther down and so let's go back and and summarize those three spontaneous reactions in the first one the ball rolled down so what happened to our H value well our n enthalpy of the system decreased what should that do to our Gibbs free energy or available energy it should decrease that value what happened here when we increase the entropy of the system or increase the Delta s well if we increase the Delta s that should also decrease the Gibs free energy so now we have two things decreasing that and what happened here well if we increase the temperature that made it more spontaneous so if we increase that we also decrease the Gibs free energy so what's the moral of the story moral of the story is that if the Delta G ever decreases or if it's ever less than zero that's a spontaneous reaction um likewise if the Delta G is greater than zero let's turn to the next slide that's going to not be a non-spontaneous reaction okay so in summary if the Delta G is less than zero that's a spontaneous gen uh reaction or we call that a exergonic reaction or an energy releasing reaction if it's greater than zero that's an endergonic reaction and then finally if nothing happens to the available free energy then it's just at equilibrium the quintessential example of a spontaneous reaction in in uh life is going to be cellular respiration photosynthesis is example of an endergonic reaction and so let's talk about each of those so let's say we're doing cellular respiration so what I said earlier is that glucose has a certain amount of energy within the bonds and so let's do cellular respiration so so I take in Sugar my body is going to combine that with oxygen we're going to convert that to carbon dioxide and water so let's animate and see what happens wow so a lot of stuff happened so let's go back so first of all let's look at the entropy of the system what happened did it become more or less ordered seems like it became more random for sure what happened to the enthalpy of the system well we're releasing energy so we have energy out here so we've released energy that means that the total energy that was contained within those bonds has actually decreased and so you can look at the value right down here the Delta G of cellular respiration is 686 kilal per mole that means if you had about a third of a pound of glucose or sugar um you were to break that down in your body you would release about 686 uh calories uh Big C of energy so we call that an exergonic reaction or it's releasing energy now we can actually plot that on a um energy diagram so glucose itself had a certain amount of free energy to start with but in this cellular respiration we end up with less energy so this is a spontaneous or an exergonic reaction now it doesn't just explode into flames the sugar that's sitting on your uh on your counter or the sugar that's inside your body and so in order to get that work to work you have to put a certain amount of energy into the system and that amount of energy we call all activation energy and so if you look back um to the first three examples I gave you the ball just didn't roll down the slide on its own you had to push it and the Cherry Bomb just didn't exploded on its own you had to little add a little bit of energy to that we call that activation energy but there's a net loss in energy and so we call that an exergonic reaction let's think about photosynthesis what do you need for photosynthesis really only three things carbon dioxide water and sunlight four things because you also need plants and so in photosynthesis what happens well we store that energy in glucose and so if we look at our Delta G value it's a positive or we call that an endergonic reaction if we were to actually draw the energy diagram of that we have a lower amount of energy to start with a greater amount of energy at the end and so we're storing energy and then it has more energy at the end in the form of that glucose now where do we get the activation energy in photosynthesis we get that from the Sun and so those two reactions releasing energy and storing energy allow life to exist but our day-to-day life doesn't use glucose doesn't use uh or we do use glucose but our second to second kind of a functioning doesn't use glucose we actually use something called ATP and so ATP or Denine triphosphate is the energy coinage of our cells it's what you're using right now it's we can we can store it as energy and then we can kind of cash it in so let me show you what happens ATP is broken down into ad DP and it releases a certain amount of energy if we look at that the breakdown of ATP to a DP or Denine diphosphate it only has two phosphates right here uh plus a phosphate group is a exergonic or the Delta G value is going to be negative if we go back and convert that ADP back into ATP now you can see right here that our Delta G value is actually positive or if we break it we release energy and then we can store that again when we make ATP again and so right now when you move your finger like this what's actually powering that muscle is ATP releasing energy allows that muscle to contract and then we can do that over and over and over again and so you use respiration to get energy but we actually store that in ATP over time so what is the secret of life and how does all of this work well energy comes from the Sun so we have a certain amount of energy up here and we store that energy through photosynthesis in sugars and so the release of energy by the Sun the Delta G is going to be less than zero it's an exergonic or an energy releasing reaction but photosynthesis photosynthesis is going to have a Delta G value that is greater than zero in other words it requires energy and it pairs that to the uh energy coming from the the sun next we make bread out of that and then through cellular respiration respiration we are going to release energy so the Delta G value now is less than zero we use that to store ATP now that ATP is used uh to break down into ADP and so that's going to be um a Delta G value of less than zero and that's going to release energy but to convert that ADP back into ATP uh it's going to be a Delta G value greater than zero and so available energy and free energy is super important it's converting energy in the sun eventually into energy that we can use and eventually that energy ends as heat um so the energy is converted that whole way through uh but it just becomes more and more disordered as we get to the end and so that's free energy and I hope that's helpful