good day good day everyone um so we meet again for another installment uh of physics in fact physical science and we are starting with chemistry and chemical equilibrium today so if you haven't subscribed please uh make sure that you hit up that subscribe button and um please you can always throw your comments um on the comments section uh if you're satisfied with the lesson and if um i always appreciate feedback by the way and if you need to get in touch with me my email address is available um that's lungisi.m.incosi gmail.com all right let's get started so today i want to cover chemical equilibrium in particular i want to just go through le chatelier's principle okay when it comes to chemical equilibrium first of all let's start by defining what is chemical equilibrium okay so chemical equilibrium is a state um when the rate of the forward reaction is equal to the rate of the reverse reaction okay so if let's say you've got an a reaction between a and b okay so uh whatever state that a and b are in right so you start by having the forward reaction beginning to take place right to form let's say a b but then um if it is in a closed system that is a system whereby there are no um the the products rather do not escape any of the products or the reactants escape right then um the reverse reaction starts taking place we call that a closed system right then the reverse reaction start taking place and and what does that mean it simply means that a b now breaks down once again to form their reactant which is um a and b respectively right so we reach a point called static or rather dynamic equilibrium or you know they simply put it as chemical equilibrium where the rate of the forward reaction is equal to the rate of the reverse reaction okay now when it comes to this we firstly know that there are three factors that affect the state of chemical equilibrium of dynamic equilibrium right so factor number one and that affects chemical equilibrium is concentration now please i want you to note this so concentration so that means by the way uh if we say concentration is a factor then that excludes liquids and solids so this will only affect substances that are in guests gestures face and the ones that are in aqueous form okay so those are the ones that are affected right so when i increase the concentration it does disturb equilibrium okay so we'll talk about that in just a few all right and then secondly the second factor that affects uh equilibrium chemical equilibrium is temperature okay uh uh temperature sorry about that temperature okay so uh by the way we've got two types of reactions uh we've got endothermic reactions as well as exothermic okay so endothermic all right as well as exothermic so i'll i'll go through this um with you so that you can see the difference between the two exothermic okay right and then the third feta that affects um chemical equilibrium is pressure okay so that's pressure so what we're going to do in this video is we're going to actually just outline and please remember this only affects guesses okay so you keep that in mind right so what we're going to do in this video is that we're going to just make sure that we have a data understanding on how each and every one of these factors that affect equilibrium when they are applied how do they affect equilibrium and how do we answer questions that are related to that okay so uh we say all right um we apply what you call the chatelier's principle right so we're going to talk about that um now what does le chatelier's principle state okay it says in a closed system if one of the factors that affect equilibrium concentration temperature or pressure if one of the factors change right then equilibrium will oppose the change and a new equilibrium will be established okay so as a result all right if we change any of these factors and by the way just to mention to you why did we not include the other factors such as a catalyst or such as um you know a surface area so surface area for instance um remember uh that affects um what we call heterogeneous reactions uh where we've got substances that are in different phases right so in that case uh normally the reactions would not be in a closed system however in this case we are only looking at substances that or reactions that take place in a in a closed system right and what we know about a catalyst is that it favors both the forward and the reverse reaction equally so it does not affect or disturb chemical equilibrium okay so what we want to do today is we just want to look at the factors that affect chemical equilibrium all right and we're going to look at how um those factors are applied in an exam situation okay right so before we begin with uh le chatelier's principle what i want to do is i want to kind of put a picture to you that will help you to apply this adequately and i promise you this picture will always make it a point that you can apply this principle in quite a nice way okay right so first of all i want us to use a model okay by the way for those of you who are teachers just remember model is never perfect okay a model is just uh there it's it's an instrument that to use uh to just illustrate a point right okay so i'm going to use a model of a seesaw okay right now i want you to think about it right so if we have a seesaw let's assume that the people that are climbing onto the seesaw uh have got equal mess right and let's put a big gigantic ball in the middle okay so there's my big gigantic ball there all right and this ball this is what we're going to use this ball for whenever uh a situation arises that's going to cause the seesaw to either to tilt either way we're going to use this c this ball to actually try and uh solve or to try and correct whatever a challenge there is okay you'll understand me in just a few okay so in this case so if i've got two people that are honesty so let's assume that they are equal in mess and therefore as a result what will happen they will just remain there and they will be at equilibrium i want you to think about that right so it means that when i when they are at equilibrium it means my seesaw is basically level okay so and there they are sitting there they're not going to push they're not going to pull they're just going to remain there so this system is level it's at equilibrium and as a result i can simply say uh um it is balanced right now i want you to think about it if i were to now make a change now please listen carefully if i were to add another child here onto the site okay right now i want you to imagine what would happen to this system ah i know that you already imagining so there would be a disturbance isn't it i've added something this side and what does it do it now disturbs so now my seesaw tilts in this direction okay now in order for me to restore again equilibrium i want it to be level again right so where should i push the red ball then our big red ball in order to try and rectify the situation again right you quite right we should push it to the right okay so i add something here and therefore i need to try and fix it right so where do i push the ball i push it to the right so if i push it to the right unfortunately i can't make animated uh you know illustrations so if i push the ball to the right what will happen it will actually try and restore that equilibrium again so if you think about equilibrium that's what equilibrium is trying to do all the time once there's a disturbance equilibrium shifts okay so in this case this ball is going to illustrate the equilibrium shift right so equilibrium shifts in order to try and solve the problem that we've created okay right and as a result equilibrium will once again be restored right that's licia talia's principle think about it he says in a closed system if one of the factors that affect equilibrium so there's a factor adding another child is disturbed right and then equilibrium will shift so what we did we do we shifted the red ball right in such a way as to try and restore equilibrium again right it shifts in in such a way as to cancel the effect as to erase the effect of the change so in this case a new equilibrium is established again okay right so i want you to always think about this okay right so um i want us to go to another scenario all right so in the same system again so think about it so what do we do let's say again we've got our two kids there playing right so there's our big ball again right now what would happen if i were to suddenly remove one of the kids okay right let's say i remove this one what happens all right equilibrium will be disturbed and as a result what happens my seesaw will begin to tilt that way again right so i wanna know where do i shift the ball in order to restore equilibrium okay right so if i remove right look at this i now shift to the left in order to try and restore equilibrium again right so that uh a new equilibrium will be established now please i want you to note let's try and and get something here so when we added something okay you remember when we added the one child right what did we do in order for us to restore equilibrium we had to move away from where we edit can you see right so when i add on one side i have to move away from where i've added in order to try and restore equilibrium can you see that okay but when i remove something okay right where did i have to shift the ball i have to shift in order to restore equilibrium i have to shift to the side all right where i have removed so that equilibrium is restored once again okay right so i want you to always be mindful of that as we take uh some couple of questions right i want you to please note how i'm going to apply the chatelier's principle all right i want you to have this picture in mind okay right so let's take for instance um a reaction wherein we've got nitrogen reacting with hydrogen okay and we form ammonia so that's 2 nh3 okay all of them sorry that's nh3 and all of them are in guess phase okay both uh our reactants as well as our product time guess phase right so now what happens according to le chatelier when i increase the concentration let's say that we reached equilibrium right so when i add more nitrogen how will that affect the amount of nh3 at equilibrium right so you're going to do the exact thing that we did right so i added more nitrogen okay so now my equilibrium is disturbed right so i've added concentration of nitrogen so now equilibrium is disturbed equilibrium says no i need to get rid of this amount of nitrogen that you've now added okay so now the reaction that favors the reaction of nitrogen the removal of nitrogen is then favored so in this case what happens then the equilibrium shifts to the right you remember when we added all right equilibrium was disturbed there was heaviness on this side so to try and counteract the problem so what did we do we shifted the ball to the right to try and restore equilibrium so we yeah just like here you added nitrogen right and then equilibrium was disturbed then in this case equilibrium shifts to the right and by the way shift to the right you can also say the forward reaction is favored so the reaction that that removes nitrogen is favored right um and as a result what will happen it means now once the forward reaction is favored look at this we are opposing the change right we added nitrogen forward reaction is favored nitrogen decreases can you see that and then but it also means that hydrogen will also decrease right why because we are using nitrogen and hydrogen but then it means that we are now going to form more ammonia nh3 so it means that the amount of nh3 at equilibrium will now increase okay right i i hope that makes sense right okay let's take the very same reaction right let's take the same reaction i hope that makes sense okay right so um if i take the same reaction again nitrogen plus three hydrogen okay this is the balanced form of it forming ammonia nh3 okay which is guess all right so all of them are in gestures phase right now notice in this case what would happen to the amount of nh3 right to the amount of ammonia at equilibrium if i were to suddenly as as the reaction is taking place if i were to suddenly let's say take away if i were to remove an amount of nitrogen okay if i were to decrease nitrogen what would happen right equilibrium would say whoa whoa you've just made a disturbance now right so now i need i need to try and um and counteract the problem i need to try and undo what you've just done what did we do we removed nitrogen so equilibrium says i have to now try and restore the amount of nitrogen that you've taken away can you see that so which reaction would favor the formation of nitrogen i want you to see right so in order for me to replace nitrogen it means now equilibrium needs to shift to the left okay or you can say i need to favor the reverse reaction okay so when i favor reverse reaction what happens then the amount of hydrogen will increase then the amount of nitrogen would uh would increase can you see that with we undo what we've just done all right but then what would it have what would it do to the amount of nh3 of course this would decrease okay right so i want you to note when you add on one side you always shift away from that side meaning that even if i were to add on the side where would i shift i'd need to shift to the opposite side right but when you remove on one side you always shift towards the side where you removed right why because you're trying to replace what you've removed isn't it so in this case when we remove this child here all right we shifted our ball to the left-hand side and as a result equilibrium was restored again all right so i'm i'm hoping that this illustration would actually make sense so that is how we treat uh the factor of concentration okay so we looked at concentration here either removal or the increase of uh um or the you know the the yes the increase of uh certain substances so i want you to please note that when we talk about concentration please note that this will only affect guesses okay and in this case aqus solutions okay so what am i trying to say to you i'm simply trying to say to you if something is in solid form or is in liquid form we will not treat it in this way we will not use a le chatelier so meaning if it's in solid form or it's in liquid form um le chatelier's principle for concentration will not be applicable in that case all right now i want us to quickly move on i hope that makes sense if you need more illustrations what we'll do is that um i'll try and give an example at the end you know that is uh that is very practical okay right let's move on to another one so um factor number two is temperature right so what uh what is the second factor that affects equilibrium so factor number two is temperature now remember when it comes to temperature we've got two types of reactions right uh i did say this at the beginning right we said we've got two types of reactions what type of reaction do we have we've got endothermic reactions okay and we've got exothermic reactions now please i want you to note this um for those of you who do not understand what i'm about to say right please you have to watch my video on um rates of reactions right so the video and rate of reactions has got this information now you remember when we talked about endothermic reactions and we illustrated that for endothermic reactions delta h okay is greater than zero i want you to keep that in mind right and then for exothermic reactions we know that delta h is less than zero meaning delta h here is positive okay whereas um for exothermic reactions um it is negative delta h is negative now i'm going to do something now and you know it just helps you with remembering um you know we always try to use aids and mnemonics you know to try and remember stuff so let's take a reaction for uh you know as an example let's take the reaction in fact yeah let's let's say if we've got ch4 plus oxygen okay um which gives us carbon dioxide and h2o right we need to make sure that this is a balanced reaction so we know we'll put a um a two there okay as well as another two there okay right now when we've got this reaction we know that the combustion of alkanes is always an exothermic reaction then we have a sign like this delta h is less than zero now please ladies and gents i want you to please follow me on what i've done okay on what i'm doing right so now delta h is less than zero okay i want you to just imagine this okay i know there's a game that we love called pac-man okay so imagine this as a pac-man okay as uh pac-man i'm just gonna put some grinding teeth on pigment right so just imagine this to be pigment and what's happening now where is my pegman facing can you see he's facing that way he's about to eat this little ball here all right so delta h less than zero just imagine pacman facing that way so it means that he's facing to the right just remember it simply means that energy is to the right so here's energy or in fact i prefer to use the word heat okay so heat is on the right okay now please i want you to note so they might ask me a question okay and say how will an increase in temperature so let's say there's a change that we make here we increase temperature okay right and we want to know how will that what will that do to the amount of carbon dioxide at the at equilibrium all right so if i increase temperature how will that affect the amount of carbon dioxide or sometimes they can even say how will that affect the yield so i want to know if i increase temperature right if i increase temperature for this reaction how will that affect the yield okay that is when we talk about yield remember that we are talking about the formation of our products okay right now this is what i'm going to do on le chatelier's principle i'll say okay look at temperature where is heat on this reaction can you see heat is on the right hand side so when i increase temperature i'm actually increasing something that is on the right hand side can you see that okay so once again i'm going to apply what we did before right so i'm going to say when i increase temperature i affect something that's on the right hand side which reaction do i now favor i'm going to favor the reaction that opposes that tries to decrease what is on the right hand side isn't it so it means remember what you said when i increase on one side i favor away from that side isn't it so an increase in temperature will favor the reverse reaction okay and so it will favor the reverse reaction all right look at what happens when i favor the reverse reaction it means i will increase ch4 it means i will increase oxygen it means now on the right hand side i will decrease the amount of carbon dioxide i will decrease the amount of h2o but it means i will also decrease what i've added which is what heat in this case so remember equilibrium is or rather the chatelier's principle is applicable in such a way that equilibrium is always trying to undo the change that you are making okay right so in this case we increase temperature and as a result equilibrium shifted to the left and as a result there was a decrease in the amount of heat that you had i hope that makes sense now um what i want to do is just to help you remember that an increase in temperature okay now i'm about to say something just now so uh um that is very important right so an increase in temperature always favors the endothermic reaction remember that okay so i'm going to show you how we'll apply that just now meaning also a decrease in temperature favors favors the exothermic reaction okay now let's go back to the reaction that we just had just now so if i look at this they gave me delta h less than zero you remember that right so they told me delta h was less than zero so what does that mean delta h less than zero is actually telling you only about the forward reaction so it means that my forward reaction right delta h less than zero we said delta h less than zero is exothermic so it tells me that my forward reaction is exothermic okay right so in this case it means my reverse reaction is therefore endothermic you got that right if i say forward reaction is exothermic delta h less than zero remember this one only tells me about the forward reaction right so if my forward reaction is endo is exothermic then it means my reverse reaction is endothermic now look at this let's interpret what's just happened we said an increase in temperature favors the endothermic reaction so look at this when i increased temperature what did it do said hey which one is the endothermic reaction ah it's the reverse reaction so as a result the reverse reaction was favored are you with me so when the reverse reaction was favored it meant more ch4 more o2 and less of your reactants similarly for this question once again what would happen if i were to decrease temperature for this reaction all right well we know a decrease in temperature will always favor the exothermic reaction right so that means which one is the exothermic reaction it means wooty it means that um it will favor the forward reaction because my forward reaction now is exothermic okay so i want you to always keep that in mind when it comes to temperature all right so when i have delta h great greater than zero it means that's an endothermic reaction right the forward reaction is endothermic that is okay so if i take a reaction such as this one you know if we take calcium carbonate okay um it forms calcium oxide plus carbon dioxide right usually okay not usually this is actually an endothermic reaction delta h greater than zero okay so usually this is solid and that is that is in solid form and that's in gas form right so in this case what will happen so i will have if i were to increase temperature for this reaction i need to now find out okay so which one is my um which one is my endothermic reaction okay so i want you to remind yourself once again there's my pacman there okay uh there's pikmin and where's pegmen facing facing on that side so where's heat it means heat is on the left hand side can you see that okay so an increase in temperature in this case would favor that reaction remember when we increase on one side we favor away from that side isn't it okay so but once again we also do know that delta h greater than zero means the forward reaction is endothermic right so we know an increase in temperature will favor the endothermic reaction and therefore the forward reaction is endothermic meaning that the forward reaction will be favored and as a result it means that calcium oxide will increase okay the amount of carbon dioxide will increase and it means that our calcium carbonate would decrease okay right i hope that makes sense let's move on to the next one so let's talk about pressure right so the final one we're talking about pressure and just remember that uh pressure only affects gases right it only affects guesses now how are we going to navigate the issue of pressure when it comes to um le chatelier's principle so um what you're going to do let's take an example with pressure so if we take the example that we had nitrogen and three hydrogen giving us two nh3 right now you need to be very careful here what we're going to do is we're always going to look on to the side that has the highest volume of guesses the highest volume of guesses now please i want you to note what i'm going to do just now right so first i want to see where do i have the highest number of moles of guesses right i can see this is a guess so it means i will include it that's a guess so i need to include it as well right so look at this it means i've got one mole of gas here i've got three moles of gas so on my left hand side i've got one plus three moles of gases so i've got four moles of gas are you with me then i check on to the right hand side how many moles of gas do i have on the right hand side i've got well that i've got only two moles of gas right now in this case we say when you increase pressure now please i want you to listen carefully when you increase pressure right a pressure increase will always favor or will always move to the side that has the least amount or that has a lesser amount of gases or that has a less volume of gases okay now i want you to look at this reaction if i were to increase pressure remember how do i increase pressure i make the space smaller so imagine you had a container that is closed like that right so how do you increase pressure you just push this thing a little bit further down and what does it do it makes the space that you have much smaller isn't it so when i increase pressure the equilibrium will always shift to the side that occupies less volume now looking at this reaction when i increase pressure for this reaction where do i have less volume on the right hand side can you see i have less moles of gas so equilibrium will say let's try and convert as much as possible to the side that occupies less volume so as a result equilibrium will shift to the right why because there's it occupies less volume and as a result what happens to the amount of uh ammonia it will increase and as a result what will happen to the amount of uh and nitrogen and hydrogen respectively it will decrease okay so similarly if i were to decrease in pressure and to decrease pressure how do i decrease pressure i decrease pressure by increasing the volume i make the space bigger all right okay so what happens equilibrium shifts to the side that occupies a a greater amount of volume right so it means in this case if i were to decrease pressure if i were to increase volume right so equilibrium would say okay where do i have the most moles of gas it would be on the left-hand side so therefore equilibrium would shift to the left okay right now be very careful ladies and gents okay let let me just take the previous example that i had used so for something like let's say calcium carbonate and we said it breaks and becomes calcium oxide and carbon dioxide okay please be very carbon dioxide sorry uh so that's solid uh that's solid so um something like this um you know when when when i usually ask learners uh to tell me how many moles of guess okay so they would say ah you've got two on the left and on the right hand side ah please be very careful you must note this will only affect guesses right so you only count the number of moles of gases on your reaction in your reaction right so in this case how many moles of gas do i have on the left hand side it means that it will be zero why because this guy is a solid and by the way even when you now look into um applying it to a kc calculation all right that's what you need to always be mindful of okay so that means in this case i've got a solid on this side so i've got zero moles of gas that's a solid as well so i've got only one mole of gas so it means that there's one mole on the right hand side the zero moles on the left hand side now please i want you to note when i increase the pressure okay for this reaction what happens all right so an increase in pressure remember we said it will shift to the side that has a lesser amount of moles of gas right so where do i have less zero is definitely less than one so it means that i will favor my reverse reaction okay so i'll favor the reverse reaction in this case why because there's no moles of gas and as a result it means that there will be less uh carbon dioxide and therefore more calcium carbonate okay right so i hope that makes sense right so what i'm going to do is that in the next video i am going to show you how to apply these in an exam situation all right for now i think um we've uh covered just what we wanted to cover in terms of le chatelier's principle and how to apply it when it comes to our three factors all right and we'll do some more questions next time until then thank you so much and please throw a comment if you understood my illustrations if you want if you have some more questions or requests please don't be afraid to even hit me up on my email otherwise see you next time ladies and gents shop