all righty my god it's time to finish off this ap chemistry nonsense let's do it okay the test is coming up on Thursday yeah Thursday it'll be epic don't worry nothing Sooners okay don't panic it's starting next Thursday don't worry door hello everybody I'm Cara and today we're going to be tackling unit six thermodynamics and it's kind of a fun chapter not got a lot also I've looked into what I'm not covered yet and basically the two videos I called tip videos are literally the full units for both units 5 & 7 so I'm not gonna make completely new videos for those because I would just be the exact same thing again so what I'm gonna do is I'll rebrand those have unit review because they basically are unit review and then there's some things in kinetics I didn't cover so I'll make that into a part 1 in part 2 and we should be guchi all right let's talk about thermodynamics did i trolled and it covered a bunch of the thermodynamics nonsense in the previous video the unit 3 walkthrough' but like I'll teach all the new stuff and did fun so the best way to explain thermodynamics is to talk about it in the laws of thermodynamics Wow I know will happen that's not expected what you played on the using of laws doesn't make any sense well you know I'm the kind of guy like to go against the grain so we're gonna explain it in terms of log ok so no one had done that in the history of the universe so first law or in fact because I'm in the zeroth law ok there is law of thermodynamics basically says that if one object is in thermal equilibrium with another basically that means that if you touch them no energy is transferred or no net energy is transferred and that means we mean that the same temperature so they're the same temperature then if the second object is the same time for the third object then the third object for the same time for the first law now you might say that's really really obvious why the heck would they make a whole nother law for that that doesn't make any sense whatsoever well the law basically only said that if one is in equilibrium with two and two we can equilibrium with three that have wanted an equilibrium with three it doesn't say anything about temperature but it allows us to define temperature right because now we get to find temperature as if they have the same temperature they're in thermal equilibrium so basically zeroth law of thermodynamics is why you're allowed to assign temperature into things or why temperature is a measure of whether things are in equilibrium with each other but honestly this one relevant for the AP exam so we're not going to talk about it much more than that all right first law of thermodynamics the way I remember what this one is that it's like the most basic fundamental thing in the universe conservation of energy pay phones it's in every single class you've ever taken in your universe so the divinity conservation of energy and that's pretty self-explanatory right you can't create a destroy energy well Einstein said you could but you know what we don't care about Einstein Einstein a meme okay I'm not a truth okay I'm sorry I'm sending my god don't worry but basically the main way that if you can makes you apply the first law is in the equation U is equal to Q plus W sorry Delta U so this basically applied for gases and this is where we're going to use it the most right so basically it's saying the change in energy of your gas is equal to the heat thing that's your gas plus the work done on the gas make sense right if you do work it gets more energy right if you add heat to it and also get some energy so your overall chain energy is how much heat you add Plus how much work you do on the main treaty part about the designing one Q is negative 1 cubed positive 1 W positive one W is negative so cute is positive one work is being done on the gas the way I like to remember it is like when will your internal energy increase it'll increase when you add heat to the guest so your internal energy improving when you add heat that mean your Q is positive when you're adding heat and negative you're taking away heat so your energy should decrease that's why it's negative when you're taking away Heat same thing for work if you punch a ball right it's gonna start moving faster right and you're doing work on the ball so basically if you're doing work on an object it gets more energy so if work is being done on the object that its internal energy increases so W will be positive let me just write it out so positive add heat and do work on ok so the one last thing you gotta know about this equation and that work is equal to P Delta B now this is more using physics honestly and chemistry is not that useful but if they ever say like the gas expands from like 0.5 meters to 1.5 liters and the pressure stay the same then you multiply the change which is 1 liter times the pressure and you're good now another quick way to calculate Delta U as I paid in three-halves and our delta T now I haven't seen a question on the AP exam that ever asked for this kind of thing but like I think you might as well know it it's a pretty useful waiting to know it also makes a lot more sense wire internal energy only depends on your temperature and how many moles you have so this happens more for Locke alrighty so now let's talk about what enthalpy is enthalpy is literally just your internal energy it's basically the same thing now technically it's internal energy plus the product of pressure times volume but you could literally think about it at the internal energy and you'll be fine so enthalpy is like written as H you can also be written as q so the first thing we're gonna talk about is like enthalpy if you think about it as Q and the one application of this is called calorimetry basically what it is is you take a cup you have water in it and then you add something to it like a salt or something that dissolves and then you can measure the changing temperature the water to see how much energy was released let's do an example right let's say you add like one gram of like NaCl and you add that to a hundred grams of water right and let's say that the water changes by trutv Celsius after we add in the NaCl and a completely dissolved let's say a positive two to be solid so it increases in temperature now I really don't know whether NaCl is dissolving an exothermic or endothermic but I'm just gonna say it's positive to to be salty that means that the NaCl released energy into the water right so that means that the reaction is exothermic so let's explain this real quick so exothermic means that the system releases energy that means that the system itself is going to lose energy because it's giving energy off so that means that your Delta H the change in Delta P is going to be less than zero and the thermic on the other hand means that you're taking in energy from your surroundings so you yourself are going to get more energy so your Delta H is going to be positive so in this case clearly is giving off energy so it's excellent so how do you see how much energy is released so basically we use specific heat so we know that there's 101 grams remember always use the grams of solution when you're talking about dissolving something and measuring how much energy right because the thing you put into the water is also a room temperature so the reaction has to heat up both the water and the thing you put into it so you got 101 grams and then you got to multiply by the specific heat and we can just assume that just Pacifica the same as a specific heat of water because adding a tiny bit of solute did not change the specific heat of water at all so this is gonna be 4.18 joules per gram degree Celsius so we multiply it by two degrees Celsius and hooray we have our answer let us calculate 844 joules now unfortunately Delta H has the units of joules per mole through per mole or kilojoules per mole but whatever so basically we have to first divide by mole to get a final Delta H of the reaction this right here is an energy released but not the Delta H of the reaction so we find how many moles of nacl so this is just going to be divided by the number of moles which is 1 over Tony him is 23 cos 30 5.45 and then we will see what this is equal to 8 44 times 27 or 30 23 plus 35 point four five is equal to 4 9 3 2 b1 which is basically 49.3 colliculus per mole epic epicness ok we did it let's go nice oh wait we've made a mistake ok so whenever you get an answer for Delta H always make sure you remember to put in the sign at the end that's how I like to do it I don't really worry about the sign before I get to the end but we know this is an exothermic reaction so our Delta H should be negative so we'll just add in the negative sign right now all right so this is our actual Delta H epic we did it now we actually did it so now let's talk about Hess's law so has a little basically says that like if you have a bunch of change in enthalpies what you could do is you could subtract them or add them to get a new chain in enthalpy so for example if I have like C solid plus like oh yeah yields co2 and that has like a joules per mole of enthalpy change and then the other one is like what's another example what about T solid plus o2 gas well we got to multiply this by to yield to see oh yeah and this has B to a per mole then if we wanted to like find out how you can make carbon dioxide from carbon monoxide what we can do is you can subtract the two equation so we literally just do a minus B here and when you negate something we're negating the second reaction so we had to flip it so now yeah instead of this we get two Co gas yield C two CS plus o2 gun wait but one second things don't cancel out our apartment is still there so we want to get rid the carbon what do we do we got to multiply the first one by two so we multiply this whole thing by two and then this becomes two a and then now we add it and we get to see oh yeah plus - OH - gasps yeom 2 CO 2 plus O 2 and then this becomes 2 a - because we added the - 8 here and now we can cancel out an oxygen on each side and epic we're left with this reaction right here and that gave us that the overall enthalpy change is just a combination of the other enthalpy changes of the other reactions so what they like to do a lot is they like to give you two reactions and they give you the Delta H for each one and they want you to find the Delta H of a third reaction that they gave you so let's try to define an example all right so this is one example they might give right all right so the way I like to approach it and I'd like to see like for each of these things right for each of the things in the reaction run upon which accreting are the in so nh3 is only in the second equation so we know for a fact that we have to bring this NH TV to the left side and we have to multiply by to something and the way we do that it'd be basically to say that we take let's call these a B and C first we got to do negative to be the negative flips the occasion and the 2 multiplied by 2 so now we have a for nh3 taken care of what about o - well okay is present in - a cleaning so let's not worry about that point and oh is only in the first equation so we need four I know on the right side is already on the right side and dissipated so we got to multiply by 2 2 plus 2 8 and now for water the only equator that had it in 3rd equated so we need sticks so then we're gonna add 16 because it's already on the right side we didn't need a x stick and then this should give our answer but if you guys wanna do it out let's just see what happens with the other thing how many n 2 2 behind so from the a we get 2 into a little right on the left side from B we get 2 & 2 on the right side and from C you get nothing so they cancel up good and you can do this for the rest of them just to check that they cancel out but we're basically done here to calculate this out by plugging in D value this for a this for B district C and you're good alright now let's talk about enthalpy information so basically what enthalpy of formation is is the enthalpy change on the reaction of forming a substance from its element so basically let's take ch4 right methane and methane is usually again so it has to be formed from carbon and hydrogen right so carbon in its normal form is solid remember that's the equation for enthalpy information has to be in the elements normal form so it has to be carbon solid this is carving gas it would not make any sense and it wouldn't be the enthalpy of formation and then the hydrogen is usually an h2 gap so we balance this put - they're good I'm basically the Delta H of this reaction is going to be your Delta H information which is symbolized like this now another cool thing to know about enthalpy information four elements in 0 if you think about it that makes a lot of sense right because let's say we put C S on the right side then what is it made from its constituent elements it's just made by itself right the left are gonna be the same things so your Delta H is that's gonna be there all right so that's why individual elements in their normal form are always zero so why is this useful well let's say we had a more complicated reaction what about combustion and methane so plus o2 yield co2 Plus water let the balance this boy real quick alright so we want to find the enthalpy change of this reaction all we got to do is subtract the enthalpy the formation so we would take 2 times the enthalpy formation of water and then we add this one so times one of the Delta H for co2 and after we've added in the products we had to subtract the reactants so minus two Delta H Oh - because they have the two over here and then minus ch4 and you really go give you all the numbers and then this is just equal to the Delta H of the reaction overall nice none another way to find the enthalpy of reaction without actually knowing the individual heat of formation we can use something called bond enthalpies and that's basically the energy stored in a bomb right we're gonna take some energy to break a bond right and also releases some energy in form of all the way my teacher explained it is like if you want to break a board like a block right you have to hit it with a karate chop and that takes a lot of energy so that's why it takes energy to break bond and then like making bomb it does the opposite so it releases energy so let's draw the structures of these so this is like speech single bonded and then oh is double bonded to each other and then co2 is like this and then h2o is like that so that's two of these there's two of these and then one of everything else so in order to go from this side to this side well we gotta do it you gotta break up these bonds so we got to bring up for CH bond and then we got a break - Oh bond o double bond and then we had a break to Co a bond for the one co2 molecule but within that one molecule is 2 co bond and then we had a break for always fun because in each molecule diller there's two bonds but there's two molecules so I got to multiply that by 2 so 4 o H bonds so we had a form ds1 we had a break these ones and it cost energy a break people so our F will be changed there's going to be 4 times the bond enthalpy of Ch plus 2 times the bond enthalpy of o minus 2 times the bond enthalpy of CO minus 4 times the bond enthalpy of H the way I like forever is that bond I hope we get really weird you gotta start from the reactants instead of the products but everything else you do products minus reactants but for bonds and enthalpy because it breaking bonds takes energy yet it's over the left and go to the right and then the other stuff is just to make sure you know the Lewis structures and then be able to count how many bought their arm all righty we are done with envy move on to entropy it's gonna be so cool entropy is kind of epic not gonna lie so entropy is basically the measure of disorder of something and basically when the second law of thermodynamics says is that the entropy of the universe is always increasing which always scared me I was like wait if it's always increasing are we all gonna end up it's like blob and something like just floating in space something oh who knows you know so what exactly is entropy so I decided to measure a disorder but to make it more clear think about it this way right let me got a solid ice right as I crystal so this crystal is really ordered they're all in rows nice columns perfectly aligned everything Gucci but when it becomes a liquid everything just sliding past each other right so clearly a liquid is way more disordered than a faller and what is a gas these guys that literally just running around they don't care this is going haywire this like recess during middle known don't even though we didn't have reset then reasons during elementary school okay so soon we a fallen is like a nice old high school crackle high school pocket are not very orderly but yeah and very orderly but then as you go to gas they have even more entropy because everything that's running around randomly the other like definition of entropy is a state definition which basically says the more possible states you have the more entropy you have so let's say we had up to like gas chambers right and we had like two gas molecules right then there's basically three positions it could be that that or it can also be like this all right let's try adding another one then there's these three options but then there's another one we can also have one on this side to the other side so now clearly the three molecules have a lot more entropy than the two molecules put in more plausible options these different things I'm drawing it called microstates but they probably not gonna ask too much about that so let us talk about how entropy applies to reactions right so let's say that we have h2o solid is melting into h2o liquid and it asks you what is the Delta s of this reaction how's it entropy change well as I explained before liquids are less orderly than solid right so they have a higher amount of disorder so they're more have more entropy so if you're going from lower entropy to higher entropy your Delta s is going to be positive let us say that you go from light what nacl solid to an a-plus-plus see on mine what the Delta s is this this is also positive because once you dissolve something is way less ordered a crystal is way more ordered than a bunch of separated ions floating in water what happens if you go from like maybe okay let's say they have ch4 plus o2 yields h2o liquid plus co2 gas well basically you're going from two molecules of gas to one molecule of gas and one molecule of liquid now liquid is feeling more ordered than gas so this is going to have a delta f of negative because it is decreasing in entropy it's getting more ordered and then one last example why Olivia like what's a good example here boss so n 2 plus 3 each to yield to nh3 so how they explained before more gas molecules needed more entropy so on the left side right now you have 4 molecules of gas right but then it goes to two molecules of gas so your Delta it negative because you're gonna becoming more and more order because I've UDP so number of molecule you're becoming more ordered all right that's why I got an O for entropy let's talk about the last thermodynamic quantity Gibbs free energy now Gibbs free energy is like the actual definition is like not that interesting but the way I think about it is a measure of spontaneity I have no idea whether I salts it right but this is not English ok I could feel however the heck I want so my spontaneity I mean like if a reaction is spontaneous it's just going to occur without any input of energy if it's non spontaneous that means that you have to do something in order to make it happen it doesn't happen on its own basically so the one thing you gotta know about gift free energy is that Delta G what did the canyon give free energy is equal to Delta H minus T Delta s this is a one-way and you got to know so know it ok do not forget this equation honestly this one you just got to do a lot of problems practice it makes you now the biggest problem I've had miss acquaintance is sometimes they give like give free energy and collegial per mole and enthalpy and total per mole but then they give like Delta s in joule per mole so it's really annoying you gotta Kerr everything to kill each other everything to Joe don't forget to convert I always does multiply this by 10 and 3 so that is converted to Joule I think it's a lot easier that way instead of dividing and then this right here is the temperature in Kelvin oh sorry this would be Joule per mole Kelvin my man all right so bigamy then just also a memorization thing a negative gives me energy means that a spontaneous so this happened by itself well okay so the other way you can think about it right don't ask is generally a positive thing right by second law of thermo a spontaneous process should have a positive Delta then it makes sense that I think be the temperature right our reaction is more likely to occur it doesn't makes more sense if your molecules are moving really fast and were likely to hit each other and do a reaction so impeding temperature will make this more negative so clearly spontaneity means that you're getting more negative because thinking the temperature makes this more negative and it also should make it worth Montaigne and then Delta G greater than zero is going to be non spontaneous alright so now that we know what Delta G means we can also relate it to our equilibrium stuff so let's say that Delta G is less than zero right it's spontaneous that means that if it spontaneous it wants to convert reactants to products so that's how reality works right that's what Iraq and does so the spontaneous enough all the time without any input of work it just goes from reactants to products so listening about reaction quotient what's Q again is basically the ratio of products to reactants kind of so if you say that your Delta Y is negative that means you favor the product hope you want to make more product so then what does that mean about cute well that means that right now your Q is too small and you want to make it bigger if Delta G is positive right that means that you don't want to go to the products in fact you want to go the other way like the pond isn't bad we don't want to go to the product so that means that your Q is way too big you have way too many products and you want to decrease a number so think that your Q is too big now there's a specific equation that relates the two so Delta G is your give me energy at this temperature then the something called Delta G standard and that favor your Delta V at standard temperature and pressure then basically if we do minus RT Ln Q we get this oh sorry there should be a plus right here let me know my doesn't make sense right and if you eat these cute you get more products right and if you have more product you want to make less of them so the reaction gets less spontaneous because you want to make less product that's why I didn't write here it's positive and add QE pieces this whole thing in pieces so your Delta G will increase making it less spontaneous and also for are always used 8.31 because for these kind of things we already SI units and also make sure that this isn't joules not kilojoules okay and then the other thing we can do is what is it any cooler well basically equilibrium always occurs when Delta G is equal to zero so if we say this is equal to zero and then this is equal to Delta G standard plus RT Ln Q well what is Q at equilibrium it's just equal to K that's a definition of cake K is your Q at equilibrium so then we got the negative RT Ln K is equal to Delta G thing so basically the things to take away is Delta G is zero at equilibrium because you don't want to go more to the products but you also don't want to go to more to the reactants the other takeaway is that as you get more products your reaction gets less spontaneous which is why as you increase Q this whole thing increases meaning your Delta G increased alrighty I think we are good that is all I got to talk about for thermodynamics let me know if you got one more in these videos as always if you enjoyed the video leave a like subscribe for more all that good stuff and I will carry out my master plan of rebranding the other two videos as you know reviews because they basically argue in a review and then I will make a part 2 for kinetics soon don't worry alrighty thinking I've been watching again see you guys next time