Gibbs Free Energy and Equilibrium - Video Tutorials & Practice Problems

Gibbs Free Energy

Hi. In this video, we're gonna be talking about gifts, free energy and equilibrium. So I'm not gonna lie. This is probably one of my least favorite cell biology topics. Um, just because it's so chemistry and whatever, and it's not really my favorite thing, But don't fret, because I'm leaving a lot of the heavy chemistry calculations up to the chemistry courses, and we're just going to spend some time talking about how this relates to Sal biology and just understanding the concepts. So we know what we're talking about when we talk about things like equilibrium. And so the first concept that we want to talk about is Gibbs Free Energy, and that is a measure to determine if chemical reaction will occur spontaneously. So what does it mean if a reaction occurs spontaneously? Well, spontaneous reactions are those which are thermodynamic lee favorable. So what does that mean? It just means that a reaction can occur without outside help, so it doesn't need anything else to happen. Reaction will just occur, Um, and so the reason it does that is because it's increasing the entropy, which is the disorder of the universe, and anything that really increases disorder doesn't necessarily need help because it's thermo dynamically favorable. So, um, Gibbs free energy can be calculated at a particular time point, which we really refer to as just a G and or it can occur. Or it can be calculated, um, regarding a change occurring during reaction, which we measure this as a Delta G. And so this strategy value changes a lot. Um, in just a single reaction, because the reaction is always moving towards equilibrium. So this these values aren't very static, but instead, they're very dynamic, depending on what point in a relation or rock point in a reaction you're talking about. And so equilibrium, um, is a state where the chemical reaction occurs equally and forward and reverse, and so, typically in chemistry, we, you know, see this a lot. Um these, you know, reactions and make these products, and the reaction can occur this way or this way. And so equilibrium is win. This reaction is occurring equally to this one. And so why do we need to know this? How does this relate to symbology? Well, um, cells do not exist at equilibrium, and instead, life depends on having reactions that are trying to reach equilibrium, but not quite getting there. And I think that that phrase right there trying to reach equilibrium but not quite getting there really expertly describe cell biology. Um and so the rest of the course, we're going to be talking about things that our reactions that are trying to make equilibrium, but not quite getting there. So when we look at a reaction, I know that, um, so or that in chemistry, they like to use letters and arrows and things that that look a lot like this. But that doesn't really make sense to me. So I'm going to show you reactions in terms of blocks. So here is a chemical reaction that's occurring. And so we have, um, here these blocks that I've stacked up and this is pretty ordered. So there's less entropy. It's very ordered. Um, and then a spontaneous reaction can occur without any outside help to create this more disordered. More entropy, so disordered, um, product. And so this is These are spontaneous reactions that occur, you know, from more ordered to less ordered, and they can occur without outside help because these blocks don't necessarily want to be stacked up, and they actually prefer to be this jumbled mess, and it's very easy to get them there compared to the energy required to build them up. So, um, now we talked about Delta G some free energy calculation. Now let's talk about the second calculation, and that's the standard free energy change. And so this also measures the spontaneity of chemical reactions. So what's the difference between the two? Well, Delta G is going to calculate for reaction and a single direction with a known concentrations of products and reactions. So in layman's terms, what this means is that it measures real life reactions. Um, and it's sort of this very dynamic thing, because react and product concentrations are constantly changing in real life reactions. It was really sensitive to those changes. Now the standard free energy change, on the other hand, calculate um, spontaneity for reaction occurring in standardized or in standard conditions. So these conditions include the temperature being twenty five degrees Celsius, the pressure being one eighty m. And so, um so why do we need that calculation? Well, that allows us to compare the thermodynamics of many reactions. Um, and so let's look, at example, of why this is necessary. So we have our blogs back. We disappear for a second. We have our blogs bag. So we're going to say this is one chemical reaction and this is too. And we want to compare the spontaneity between the two. Now, this can be really difficult because these blocks are different. They're different sizes. There's different numbers. There's, um they're different colors. So these are two completely different reactions. But we want to say which one is more spontaneous. Well, if we calculate just the Delta G, this is highly dependent on concentrations, which you can already tell are different between the two. So if we use the Delta G to compare, we're not actually giving a good representation and a good comparison of the two reactions so we don't use we don't use that value. We don't use the Delta G. Instead, we use the standard free energy change, which I realized I wrote that wrong. So we don't use the Delta G No, don't use that and instead use the standard free energy change to compare these two. The spontaneity of these two reactions. Let me come back to talk about this, uh last concept here before we turn the page. And that is the concept of eggs, organic and inorganic reaction. Now you're probably familiar with these terms from chemistry, but let's just review them real fast. So extra panic reactions release energy and inorganic absorb energy. And so because energy is being released, it released in eggs organic reactions that means they're more thermodynamic lee favorable. And so, if we look at a just a standard reaction with reactant since going to products U C. T s, then the free energy of products will be less then the free energy of Iraq tints and the Delta G will be negative. And so for inorganic reactions, you know, it's an inorganic reaction by looking at the Dell G value because it will be positive. And so that means that they're less thermo, dynamically favorable, and the free energy of the product is more then the free energy of reaction, a reactant and so, uh, mention equilibrium again, Um, the delta actually is zero, and so no reactions occur. So let me disappear while we look at these graphs. Now, I'm sure you've seen these graphs before, and sometimes some of this might be a little difficult to see, but essentially what you have is your reactant and your products, and the same is over here you're reactant and your products. Now, for an extra chronic reaction, this is energy releasing. And this is because the free energy, which is here on the Y axis and you're looking at the reaction of moving forward, the reaction the free energy of the reactant is higher with all the way up here compared to the free energy of the products which is all the way down here Now, this is exactly opposite for the inter chronic reactions where the free energy of the reactions is really low and the free energy of the products is really high. You can see this up here. And so, um, extra organic reactions release energy. So they're releasing this energy from the reactant to the products, whereas in organic reactions are energy absorbing. So they need energy because the products have a higher level of re energy than the reactant in order to occur. So now Anderson, that let's turn the page

Equilibrium

Okay, so in this video we're gonna talk more about equilibrium and specifically we're going to focus on this equilibrium constant and what this is a measure of is the right of products to reactant. So if we go back to our chemistry drawing of a chemical reaction equilibrium is when the forward and reverse reactions are occurring equally. And so how we can know whether or not that's going to happen is looking at equilibrium constant because that actually measures, you know, what's the proportion of products to react in. So this is really important measure of directionality. And the reason that it is is because if we have these reactant and we have these products, if there are more products than reactant, then it's going to move this way in order to equal out the amount of reactions and products. Whereas if there's more reactant than products, it's going to move this way because then um because it wants to equal out the amount of products. So the number or the value of the K Eq can actually help determine the directionality. So Um we can see that when K. Q. is greater than five, then the reaction occurs in reverse. If it's greater than .5, it occurs um or less than .5, sorry, it proceeds forward. And then if it's at equilibrium, no reactions occur. So those numbers are kind of, I get, you know, arbitrary, they don't really mean anything. So let's um let's actually look at a reaction here. So we have three reactions. So let's figure out you know what the K. E. Q. Is for them. So at equilibrium the reactions are occurring both forward and reverse equally. And so the K EQ is going to equal 30.5. Let me move out of the way, sorry for that equal 0.5. And that's kind of easy to understand. But let's look at these other reactions. Now when um the reaction is moving forward, more is moving to make more products then what is the K. Q equal? So the KEQ is going to be less than .5 And then that's going to be opposite of course with the reverse reaction. So when the products are more and the reaction is moving in reverse the KEQ is going to be greater than .5. Now let me come back and talk about another concept and that is steady state. So in steady state is not equilibrium and I think that's really important to understand because we're very familiar with study state, are very familiar with the equilibrium but not so much the term steady state. So what is steady state? Well that's actually the stability of concentrations of reactant and products. So um for equilibrium, what we can see I'm gonna draw this again here um that these reactions are occurring the same but at steady state um there can be a much higher concentration of products or reactant and a low concentration of products but as long as these concentrations stay relatively stable, this is occurring at steady state. So in cell biology, what does this mean? Um Well we can talk about this in terms of nutrients for example coming into a cell now the reaction of nutrients actually coming into the cell isn't equilibrium because they're not equally flowing in and out of the cell, they're only flowing one direction so um they're flowing into the cell so not at equilibrium but they can be at steady state if the concentration of nutrients outside the cell inside the cell remain relatively stable. So when it moves in there could be a really high concentration of nutrients outside of cell and a really low concentration inside. But as long as it maintains those concentrations it's fine it's still it's steady state but it's definitely not happening in equilibrium because there's not an equal flow and there's not this movement towards equilibrium. We're trying to get the products and react in the same concentration on either side because that's not going to happen in terms of nutrients a crossing crossing a cell membrane. So that's a so that is equilibrium and study safe. So now let's move on

The standard free energy change (ΔG°) measures which of the following?

• A. Spontaneity of a chemical reaction under any condition
• B. Spontaneity of a chemical reaction under standard conditions
• C. Ratio of products to reactants
• D. Disorder in the universe

The above energy diagram represents what type of reaction?

• A. Exergonic
• B. Endergonic

True or False:In an exergonic reaction, ΔG will be positive because energy is being released.

• A. True
• B. False

Which of the following ΔG values represents a reaction that is most likely to occur?

• A. 30
• B. 250
• C. -30
• D. -250