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Current time:0:00Total duration:11:52

Endergonic, exergonic, exothermic, and endothermic

Video transcript

so we have some words here that relate to different reactions and whether they absorb or release different types of energy so the first word here exothermic exothermic the root of the word is therm which relates to Heat and this word indeed means a reaction that releases heat releases releases it releases heat and one way to think about it if you're thinking about constant pressures or change in enthalpy it can be viewed as your as your how much heat you absorb or release so a negative change in enthalpy negative change in enthalpy means that you're releasing Heat one way to think of if you view enthalpy is heat content you have you have less heat content after the reaction than before it which meant you released Heat which means your change in enthalpy is going to be less than zero so these all mean the same thing well this this is true you're releasing Heat this is the same thing as releasing Heat if you talk about constant pressure constant pressure which is a reasonable assumption if you're doing something in a beaker that's open to the air or if you're thinking about a lot of different biological systems now based on that logic what do you think this word means endothermic well endothermic endothermic therm same route and now you're prefix is endo so this is a process that absorbs heat absorbs absorbs heat or if you're thinking at constant pressure you can say your enthalpy after the reaction is going to be higher than the enthalpy before the reaction so your Delta H Delta H is going to be greater than greater than zero alright fair enough now let's look at these two characters over here exergonic and endergonic so X organic the root here is our gone and that you might not be as familiar with that as you are with therm but you might have heard the word economics say hey that's a nice ergonomic desk that means it's a desk that it's good to do work at it's a nice ergonomic chair and Ergun does indeed come from the Greek for work and so exergonic is a reaction that releases work energy or at least that's what the word ize releases releases let me do that in the same color this is something that is going to release release work work energy energy and endergonic same logic well that's going to be something based on just the word the way the word is set up that absorbs work energy or uses uses work work energy now one of our one of our variables or properties that we can use to think about energy that can be used for work is Gibbs free energy and the formula for Gibbs free energy if we're thinking about constant pressure and temperature so let me write that down so if we're talked about constant constant pressure pressure and and temperature then the formula for Gibbs free energy or you can even view this as a definition of Gibbs free energy the change in Gibbs free energy we do this in another color the change in Gibbs free energy is equal to our change in enthalpy our change in enthalpy - - is in the different color - our temperature - our temperature times our change in entropy and if this looks completely foreign to you I encourage you to watch the video on Gibbs free energy but the reason why this is related to energy for work is okay look I have I have my whether I'm absorbing or I'm releasing Heat and I'm subtracting out entropy which is kind of the energy that is going to the disorder of the universe and what's left over is is the energy that I can do for work that's one way to think about it and so you can see that this relates work energy to change in enthalpy right over here and so exergonic exergonic something that releases work energy you could say that it has less work energy after the reaction than before it your delta g is going to be less than zero so let me write that down so here our delta g is going to be less than zero these things these reactions that release work energy we've seen it in the video on Gibbs free energy we consider these to be spontaneous spawn spontaneous these are going to move forward and so these over here the ones that absorb work energy well they're going to have more work energy in the system than before is one way to think about it and so your Delta G your Delta G is going to be greater than zero and we say these are not spontaneous so these are not spawn spontaneous so now that we have the definitions out of the way and we have a way to relate these variables let's look at these different scenarios of things that are exothermic and an exergonic or exothermic and endergonic and see why they make an intuitive sense so in this first reaction it's exothermic our Delta H is less than zero that means it has less enthalpy after the reaction than before which means it released Heat and so you can see here this heat is being released and where does that energy come from well when the when the when it bonds in these new configurations on a net basis the electrons are able to go to lower energy states and release that energy and heat if you're thinking about on a microscopic scale it's something that's raising a temperature at least locally which it means just about transferring kinetic energy to these two these microscopic molecules remember we talked about heat or temperature you're thinking about these macro variables but on a microscopic variable you're talking about kinetic energies and potential energies and things like that so what's happening is these electrons or when they get into a new configuration and they're going to they're going to release energy and that can be transferred to the individual to the individual molecules and so you see here we've released energy and we also have an increase in entropy we have more entropy after the reaction then before the reaction we have more we have more objects all right over here there's more states in which they could actually be in and they're actually moving faster and so this one we see if you just apply if you apply the formula over here this is going to be less than zero this over here Delta s is going to be greater than zero the temperature that's going to be absolute temperature in terms of Kelvin so it's always going to be positive and so this whole term is going to be positive so you're going to have a negative minus a positive is going to be negative so our Delta G our delta g is going to be less than zero and we see that this is spontaneous this is going to move forward and it makes sense it releases energy the electrons like it it creates a more disordered state I think another way to think about it is think about trying to do the reaction the other way you're going to have to get some energy for those electrons to get into a higher energy state when they form these new bonds you're gonna have to get these four constituents together in the exact right way that seems that less like a lot a lot less likely to happen than going in from the left to the right now let's think about something that absorbs heat and this one's a little bit counterintuitive it absorbs heat but it's still going to be spontaneous it's still going to be exergonic it's still going to happen so Delta H is greater than zero so it absorbs heat to happen so I have these two molecules with these different constituents they're about to collide and we're saying that the temperature is high if the temperature is low this might not be spontaneous but if the temperature is high enough it will be so the temperature high on a microscopic basis you're saying okay these things just have a really high kinetic energy they're going to ram into each other really fast and they're going to ram it to each other so fast that they can form all these other constituents in so that you have the you have the net entropy you have the net entropy has increased and even though over here our electrons are in a higher energy state to form these configurations so it had to absorb heat so it had to absorb heat energy so we could say heat but heat on a microscopic level we're just talking about kind of kinetic energy of these molecules so it has to absorb it but where where did that where did that energy come from well it came from the kinetic energy of of the molecules they might have been they might have a certain kind of cat energy before but then some of that gets lost so when they all get banged up into their different configurations and if you're saying well I still don't get this think about trying to do this reaction the other way try to get these four constituents in the right time all together even though if they're happening if they're if they're if they're put together at the right way their electrons could configure in a way to release energy but this is super high temperature this is a really really chaotic system it's not going to go from right to left it's going to go from left to right when it's really chaotic things are banging each other really fast you're more likely to go in the direction of a higher entropy so now lookit now let's look at the and so this is spontaneous even though it absorbs heat it absorbs heat if you're not draining the heat away locally your your your temperature or at least around these molecules it will go down but of course we assume we're assuming constant temperature for this so you can zoom that you know on a macro level that temperature dissipates and gets absorbed outside of the system somehow now let's look at this configuration it's exothermic so Delta H is less than 0 less enthalpy after the reaction than before so it's releasing heat but it's not spontaneous and it's not spontaneous because it's reducing the entropy in the world it's reducing the entropy in the world and the entropy matters because our temperature is high one way to look at this equation is entropy doesn't matter when temperature is low temperature is really scaling your entropy but when when temperature is high entropy starts to take over this variable starts to matter a lot and so over here because entropy is negative this isn't gonna this things are not going to actually happen so if these things were coming together very slowly their electrons could configure in just the right way so that they can get to a lower energy state and release energy but they're buzzing past each other so fast that they're not going to have a chance to do that and if you think about it the other way this reaction is much more likely to happen if you have a bunch of these diatomic molecules running around they're going to bump into each other so fast that they're going to knock they're going to knock the constituents off of these off of these diatomic molecules or at least the way of depicted it kind of looks like a diatomic molecule and they'll that might absorb some of that kinetic energy and doing it in order to go from right to left but that's more likely to happen so from left to right not spontaneous because entropy really matters at this high temperature and then finally and this one's pretty intuitive something that needs heat something that needs heat energy and has a reduction in entropy that's definitely not going to be spontaneous so this is greater than 0 this is less than 0 which but then you're subtracting it so this whole thing is greater than zero this Delta G is going to be greater than 0 Delta we do that in that green color this Delta G is going to be greater than zero and it makes sense that you have these two molecules they have to get together in just the right way they need heat in order to proceed with this reaction to kind of excite to excite the electrons to higher energy state to get into this I guess you could say less stable bond why would do why would they do that the reaction is much more likely to go in this way where if you had a bunch of these molecules they're all knocking into each other they get to a more stable configuration and there's more entropy when there's when they when they split up then when they actually stay together so Delta G greater than 0 this is endergonic and endothermic and of course this one was Delta G greater than zero even though this would release energy the the the things are so chaotic they're not going to have a chance to do that and you're much more likely to go in the direction of of maximizing entropy and so this one also is not spontaneous
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