Transcript for:
Lattice Enthalpy

[Music] [Music] hello my name is Chris Harris and I'm from a Lurie chemistry and welcome to this video on OCR a lattice enthalpy so the whole point of this video is to go through some of the the main points of lattice enthalpy specifically for OCR a so it's a revision video and everything you see on here is dedicated and specifically to OCR a and this isn't the only video there was a range of videos that covers the full exam board for OCR a four year one and year two it's all on the YouTube channel Allawi chemistry it's all for free to all I ask you to do is just to subscribe just hit the subscribe button and then show you support all of this is completely free like I say and though you can get a hold of these slides though the slides can be useful for if your bump you got your tablet if you've got your phone or if you've got anything like that way you can revise on the go and they can be purchased separately as a PowerPoint presentation if you click on the link in the description box and you can get a hold of them there um but like I say the whole video these videos are purely designed to go through OCR OCR a lattice enthalpy in particular and the particularly designed if I could spit it out and there's particularly designed to go through the through the content so for that reason they do adhere to the specification and this is a specification for this topic which is looks quite a scary topic with their born here but cycles etc there's a lot of a lot of information in there and there's a lot of definitions that you need to remember but we'll go through it anyway and it's a really quite a 16 summary for this topic particularly for this example it's a perfect if you study in OCR ok so let's get started so we're going to look at and the types of enthalpy change okay now you will have seen enthalpy in year 1 chemistry and so this one's looking at the different types this that you may have seen before and some which you won't have done and this will all become apparent shortly so the first one is the enthalpy change of formation now you may have seen this form Hess's cycles yes they vendor something but no they're not they're actually alright if you know how to them if you're not sure that have a look at the video I've done loads of videos on Hester cycle within a lyric chemistry so you go and have a look if you're not too sure and so anyway enthalpy of formation which is Delta F H which is this but here Delta means change in F is formation H is enthalpy and so the enthalpy change when one mole of compound is formed from its elements in their standard states under standard conditions now what you'll see is a lot of these definitions have this at the end standard state standard conditions and make sure you add that bit definitions are vital you've got to remember your definitions the ones that have cluded on here are the ones that you need to remember there are were the ones but the exam board as likely to are likely to give you them but these ones you definitely need to remember okay so don't don't and be change of formation we'll use these later on these are just literally definitions lattice enthalpy of formation now you might not have come across this one but we give it you'll notice a pattern here we have lattice not lettuce lattice in the middle Delta which is change in enthalpy obviously is there this is the entropy change from one mole of a solid ionic compound is formed from its gaseous ions under standard conditions okay and we've got an example here again with definitions like this the best things to do in context and so we will see where these fit in later so don't worry too much about it we do need to know the definitions but don't worry about where it fits in for the time being at least so the next one is ionization now you would have seen this one in year one about the ionization of substances or removal of an electron so this is the enthalpy change when one mole of gaseous ions Geisha swamp plus ions are made from one mole of gaseous atoms okay so effectively we're removing an electron from from an atom and it's the amount of energy so moving one mole of electrons from last now the reason why this one mole and standard states is relevant is because these are factors which can affect the amount of energy required to conduct the action that we're describing so if we had one and a half moles with one thing in two moles for another then obviously the two moles is going to take more energy than one and a half so all these different elements here these caveats are supposed are in there to really emphasize that the standard conditions must be met okay so let's look at iron ik bonding because this is going to come into play quite a lot when we look at enthalpy and energy and the structure of substances and the energy required to break them or put them together so this is why this is important and so the size of the charge on the iron affects the strength of the ionic bond okay so the bigger the charge the bigger the charge on an eye in the strongly electrostatic attraction between the iron so that make sense so some of the two plus charge it's kind of a bigger it's gonna have a bigger electrostatic attraction with a two - then a 1 + and a 1 - so it's about the size of the charge which has it which has an impact note would say more energies required to overcome these forces so they have higher melting and boiling points and this is classic things like sodium chloride is a is a as an ionic compound I don't if you've tried to melt sodium chloride in a pan but it is incredibly difficult to do that because it's not a compound it requires so much energy to break the ions the sodium chloride ions apart from each other and that it really has a really high melting point so his potassium chloride so AB this also table salt so k+ + CL - has a melting point of 770 so as a one plus and one minus calcium oxide is made up of CA 2 plus an O 2 - we have a two positive and two negative charge and this is a melting point of 257 - so it's significantly bigger so the effect of that is the the main effect as the size of the charge on the respective ions okay so the size of the iron so the ionic radii is the basis of the radius so it's the size of the atom and that does affect the strength of the ionic bond as well so the small of the iron the strongly electrostatic attraction between the ions you've got to get used to using this terminology as well electrostatic attraction so these are key terms that you must put into your answer just get used to integrate in the middle you answer try and think when you're putting the word down try and think is there a scientific word that I can use describe that sounds very very geeky but you've got to make sure you include these words because the exam board gives you marks for using key words talking like a scientist so the smaller ends they can pack together much more effectively so they really can squeeze in and so that means there's more energy required to overcome these stronger forces that were effectively holding them together and the melting and boiling points are significantly higher as well as a result so a classic example of sodium chloride which na+ and cl- as a mountain point of 801 but if we take potassium chloride now potassium is bigger it's a big wine then the melting point is actually low at 770 we can't pack these ions in closely enough and so therefore the the melting point is reduced as a consequence of that so generally the small of the iron and the higher the charge the stronger the electrostatic attraction and hence the higher the melting point and so we say what they've got is a high charge density so if they've got if we've got a two plus charge in a smaller ion there's a higher charge the high charge density in there because we've got the same charge but in a smaller area okay so that's quite important there's a lot of keywords here and really what I've got to emphasize is key terminology in this such as charge density such as radii such as electrostatic attraction and such as charge so things like that okay so this is where said we're going to apply some of that terminology that we've seen their definitions we're going to apply it into the born-haber cycle now the born-haber cycles look really really complicated but the key thing is to be methodical okay and the definitions really learn your definitions through doing born-haber cycle so you're doing two things at once trying to learn definitions is it's probably one of those boring things you could do and also is really difficult to actually learn definitions you know off scratch unless you're literally drumming it into your head over and over and over again it becomes a bit monotonous and boring and you end up just not doing it so the best way of doing it is actually by doing a born here the cycle which is slightly more interesting because there's lines and hours etc but also you actually you're you know when you drawn up you're born here but just think of the definition look at the definition and look at the step that you're doing and it really does become a little bit more easier look the easier to remember okay excuse me okay so born over cycles are useful to calculate lattice enthalpies so this is because can't calculate this directly from experiments and so it is structured in a particular way okay okay so let's look at the first bit so the basic thing the born here recyclers right at the bottom of the cycle we always have the ionic solid okay so in this case we're going to basically break down the formation of lithium of lithium chloride here or well little chloride is is the salt but the actual intricacies of how we make lithium chloride or how lithium chloride is broken down is actually in a various different steps and so what we're doing here is we're showing how this can be structured so the first one so you can see here we've got lithium going lithium and half chlorine go into lithium chloride solid so we've got lithium solid because that's how lithium normally exists and chlorine as a gas because that's how chlorine normally exists but chlorine always goes around as a pair okay so we must but we only need one for lithium chloride so we must put half in front of the CL two because we only need one chlorine not two of them okay so only forming one lithium chloride now this reaction shows us the enthalpy of formation okay so we're forming now if you can remember this from our definition we're forming a solid we're performing a solid compound here which is lifting clothes from elements in their standard States okay so this is what states these elements would normally existed at room temperature and pressure okay this step is always exothermic okay exothermic means negative so Delta Delta Delta H it's negative value so that means when we draw our arrows on our born here beside cold we always draw EXO thermic processes as a downwards our in other words energy if you imagine this is energy along the side here and you might see that in the examinee and put it on here but energy is that effectively been lost it's decreasing it's negative it's going down so all exothermic processes are negative and or exothermic sorry all downwards ours are negative and all exothermic processes are negative ok so let's look at another step so we're going to go the other way ok so let's say for example if we want to form this theme chloride we can take these elements lithium and chlorine and we can form this theme chloride through a formation reaction but we can also go another way as well and this is going an opposite way so there's always two routes it's a bit like so my closest town is Newcastle so the closest town that's the city so my closest cities Newcastle so I don't get to Newcastle a few ways I can I can either drive down the a1 and get Newcastle that way art and go down the year 19 so I can go two different ways and it's the same chemical reactions you could go one way which is for example lithium lithium plus half CL to two lithium chloride what and go the way which I'm going now with the blue arrows so this way what were the first step we do in the born-haber cycle is enthalpy of atomization so what we're doing is we're taking lithium and I saw we've taken chlorine sorry and we're atomizing chlorine no atomization is always an endothermic reaction okay so that means heat energy is required to do this step so what we're doing is we're effectively breaking the bond between the chlorine atoms and turning it into an atom so we call that atomization so this is an endothermic process the arrows going up because it's positive okay the higher up the scale we go the more energy is required so basically this is going up okay so now we now need to atomized lithium because we've got it in a solid ideally would like to get it into the same stakes it's easier to handle now this is theoretical of course it is it's theoretical but what we're trying to do is work out the is work out the actual energy required to do this so enthalpy of atomization of lithium this is an endothermic process so that's my also means converting things that are not in a gaseous state into a gaseous state so victory we're breaking apart the structure of lithium solid and turning it into lithium gas and that requires energy it's an endothermic process okay the next step is to form ions because we need to form lithium chloride and lithium chloride is an is an ionic substance so we've got to make sure that we form ions to do this so to form ions we're going up to form lithium plus CL and electrons so this is ionization energy it's the thirst ionization energy for lithium and to remove an electron from lithium requires energy again so this is an endothermic process so we'll form and lithium gas chlorine and electron now you might be starting to see something similar here where we are effectively forming lithium Cloyd from ions in the gaseous state so remember that definition from the first one so this is so that it's the air blattis enthalpy formation and so what we're trying to do here is for mines in the gaseous state but we have to do it step by step so what do you think the next step is going to be well what we have to do is create a negative charge and chlorine so this time we're going to add the electron that we've removed from lithium to chlorine now do you think that will be an endothermic or an exothermic process well that one's going to be exothermic and the reason why is we're adding an electron to chlorine remember chlorine has seven electrons in its outer shell if we're looking at on that on that on the Bohr's model scale and it has seven electrons in the outer shell it is desperate for another electron so it's not going to put up a force to receive an electron and in fact it's it invited the electrons to be part of the atom and so energy is released when we add an electron to chlorine so this is electron affinity we call it so affinity just means to attach or to if you have finit eyes with something and it means you're associated with it so this is electron affinity and it's an exothermic process for this one here because we're adding an electron to an atom okay and so the final step look what we've got here we've got ions in the gaseous state so now we can go for the final process of using these ions form lithium chloride and so we call this the lattice enthalpy of formation of lithium chloride here so that was one of the definitions that you have to remember is the lattice enthalpy of formation and you can see perform it from the ions in the gaseous state to lithium Clyde okay so what the exam board will want you to do you may think well so what and what the example want you to do is is construct baby's part of a cycle they might have put some of it there or maybe it's not even construct on at all and just use figures and use numbers to actually calculate the different parts of a cycles for example they might say right here's the information here we've calculated the enthalpy and the enthalpy values of something so for example we've given you the other figures here but not for lattice enthalpy we want you to work out this bit then you have to use this cycle to calculate it that's really what the exam board are looking for okay so it is very when you're using it and it is very much like a HESA cycle okay so you remember with hasser cycle when you go with an arrow you keep the sign the same when you go against and out well depending in the direction you're going you flip the sign the opposite way so for example if it's positive going forwards if you go against that or you go negative okay the value stays the same it's just the sign in front of it changes so what I encourage you to do if you're ever a little bit lost because this is just like a giant Hess's cycle effectively it's just a Hester cycle that's broken down into more bits the principles the same okay so that makes it a bit easier but if you're a little bit rusty on Hester cycle or I encourage you to do is to go and have a look at the video and that I've made in year one and the one video for OCR that looks into M has to cycle as well I've got some whiteboard videos as well with Hester cycles so go and have a look at them as well okay so let's look at the calculation side because I said the treat them the same as has two cycle and have a look and see what you think and if you have a bit stuck let's say go back and have a look so we calculate let's lattice it let it I'm gonna stop seeing letters lattice enthalpies by using the cycle in the zoom way as Hester cycle so go with the owl keep the sign the same and go against the owl and you change the sign not bitter what I said just before so let's have a look at the same cycle that we looked at before that we just constructed obviously we've broken it down to the different bits and we know what them parts mean so the enthalpy change of sorry the enthalpy change and the enthalpy these are the different parts of the cycle but the difference is what we haven't done is we have labeled them here but we haven't labeled them on the side here so this is first of all this is why I think it's useful to do the cycle first you born here bet and then learn the definitions from there because actually you can see where these fits by looking at a cycle like this and then subconscious we're not kind of subconsciously you then remember the definitions so we're going to be a formulation of lithium chloride first ionization entropy of atomization of lithium and the chlorine and electron affinity and we've got the values here okay so you'll be given these values you don't need to worry about it okay so let's look at the first one so enthalpy of formation is minus 409 okay and remember so it is before we four we carry on what we're calculating is the lattice enthalpy okay so remember lattice enthalpy if you can if you can remember from the previous slide but a lot of times B is this bit here this is your lattice enthalpy so we're forming it we're forming performing it here so we'll want to work out this value here so what we're going to do is we're going to take these figures here and basically just fill them in on there and then we're going to use the cycle to calculate that so enthalpy of formation is here first so this bit this bit here is your atomization because what we're doing is we're atomizing a chlorine to chlorine okay so we take that figure there which is one to one now the reason why it's one to one and this is a really really important part is the data they've given you is the atomization of chlorine cl2 we are only atomizing to get one atom of chlorine so we have the value there it is vitally important that when you get this data that you check to see what that data is actually asking you to do so this is asking you to and the enthalpy of atomization of chlorine it's two for two but we're only after one chlorine so it's one-to-one really important to check the data it might say attentive optimization and it might already works out as chlorine one asks Maclaurin so really look at it carefully in this case we have to have it okay so the atomization of lithium is one six one because we're turning lithium solid to Lithia gas and then we've got our first ionization energy which is five one nine and then our electron affinity which is minus three six four okay so we've used the data there and really you do need to know what is what which is which so we can put this data in if you don't then you get a struggle but at least by looking at it you can see how it's structured so we need to calculate the lattice enthalpy formation of lithium okay lithium chloride sorry so that is Delta lattice hitch okay so what we're going to do is we're going to use it in a similar way to Hester cycle and so like I say there's two ways of getting there okay but imagine it is a bit like a roblox he'll go back to me previous example about my nearest city was Newcastle so aren't neither go down the a1 won't go down the year nineteen now the year one is a nightmare to get down so sometimes a nineteen zzo but you come in from the wrong side but um so let's assume that the ear one is closed and I have to go down the year nineteen I'm taking an alternative route it's longer to get down the NIE and it's shorter to go down the a1 but it's the same with Hester cycle I could go two ways now imagine one of them route is one of them routes is closed so I want to work out going from here to here okay this is where I want to go but what we've got to imagine is because we don't know the value of that you imagine that that's a roadblock so that's like the a1 closed so what we've got to do is go down the year nineteen or we're going to go the opposite way so we're going to go this way round here round here and we're going to get to the same place it's just going to take us a little bit longer but what we're going to do is we're going to go by a certain and via certain spots and every time we go a stage we've got to take into account the number so we're going to start from here and we're going to go against the arrow now we know this is minus 364 because we're going against the arrow then and we're going to flip that two plus three six four so there it is okay so us three six four then we're going to go down on this side here because we're going against the arrow here because this is the direction of travel then we're going to go five one five one nine so this is going to be minus five one nine yeah minus five or nine we're then going to go against the arrow for the next one so it's minus one six one there it is we're then going to go against their will for the next one so it's minus one to one this is a lot of minuses here and then the last step were gone with the owl for once for this one so this is going to be minus four oh nine so we keep it as minus four a night okay so there it is there so we've eventually arrived at our final destination we've arrived there and we've just taken a longer route to get there so the absolute value is going to be minus eight four six kilojoules per mole so it's still an exothermic reaction but what you can do and this is the great thing about it is we can start anywhere on the cycle and we use the same error rules as we've done there and we should always always always get a value of zero okay so this is a effectively a bit like if you do maths is like vectors okay and if you add them all up everything should add to zero effectively or even physics if you do displacement in physics then you'll know because that's a vector quantity and then you'll know that it always adds up to zero so it's effectively like it's a bit like me going to Newcastle and then come back no more per Sullivan morpeth coming back to marbeth and affect our trek it's about 16 miles from Auckland to Newcastle and then 16 miles back I've traveled am 32 miles in total but my total displacement is zero I haven't actually really got anywhere I've gone to Newcastle I'll come back so it's the same with a cycle as well so everything adds up to zero you haven't actually moved anywhere you've gone to the same you've got the same step so effectively this is and we add all these up and all of these numbers here providing media to the rules should add up to zero so try it if it doesn't add up to whoa something's gone wrong so just go back and check and have a look it's always worth the effort just to make sure that you've got it right if you do get a zero you either and it more than likely it's going to be right if you do get a zero and if you don't get zero and it's wrong then you probably the unlost and luckiest person the luckiest person should I say in the world because to get out of all the numbers that you could get by fluke zero M is very difficult so always check so if you put all them numbers in and just put all them together and they should add up to zero okay and also just check the figure this is minus eight four six that makes sense because this is a negative value remember because it's an exothermic so we know it must be negative it can't be positive and because it's always exothermic so always check that okay so let's imagine we take another cycle and we're going to calculate a different part of the cycle so they would calculate at lettuce and lattice enthalpy I will stop saying letters of promise at lattice enthalpy and then and then what we're going to do is we're going to work out a different part of that cycle so remember go against the arrow we change the sign okay so here's the formation of sodium chloride this time so it's a different cycle and we've got our data as normal so we're going to work through that cycle again so we're going to start with our enthalpy of formation this time and we're going to work out we're going to work out something different here but we're going to work well that is in a moment but what we're gonna do is put in all these data in to see what's missing so we've got our enthalpy of formation and we've got our atomization of chlorine again we have it because we only want one chlorine atom we need to calculate the atomization and to be here because we don't have data for that and we've got our ionization energy we have that and we have our my our electron affinity sorry we've got electron affinity and we actually have our lattice enthalpy here so we've got everything here but we need to work out this bit here okay so remember this is the route that want to take we want to go from here to here because that's the bit we don't know but this road has been blocked so this is like the year 19 is blocked so we have to go down a 1 instead so we're going to go from here to here but if this is blocked the only way we're starting from here so if I put it on there they go starting from here that's where we're starting from if we can't go this way directly we have to go in directly so we have to go backwards backwards up up and then down okay to get to the same place so let's have a go so we're going to go down so we're going against the arrow so it's minus 1 c1 we're going with the arrow here so that's minus 4 1 1 we're going against the arrow on this bit here so that's gonna be plus 7 8 7 there it is we're going against the arrow here so that's plus 3 6 4 there we are okay and then we're going against the arrow here so that's minus 4 9 6 and then eventually we get to where we need to be we'll get to our final point so then if we put all of that into a calculator we should get our final value of plus 1 2 3 kilojoules per mole check to see if that's right that is positive okay so that's an arrow pointing up so it should be positive we're getting negative that's the first thing first check point that's not right then all you have to do is take all these numbers here just trick them into the calculator and they should add up to 0 it's magic ok and remember if it doesn't just go back and check it's worth it is absolutely worth the effort it gives you that confidence that if you do get that right then you know you've definitely got it right because the chances are if you get something as 0 and you've got it wrong as it's very unlikely ok so here's another born-haber cycle ok of born harvest I got everyone to pronounce it 10 tomato tomahto right so um it's an extended born-haber cycle but it's for ionic compounds made up of two double ions so this one's gonna be magnesium 2 plus no.2 minus okay now this looks a little bit more complicated but just bear with me you follow exactly the same rules we're just adding a few extra steps in here because we have to ionize twice and we have two electron affinities twice because we're forming a - - and a 2 plus that's the only difference okay this bit looks a bit scary but I'll explain ok it's easy marks okay it's a real good to the examiners love this okay so here we go so notice we've got the second ionization step like to say so this is needed because we need to create that mg 2 plus sign and this is an endothermic process okay heat energy is required to remove that second electron so we've got that extra step there and likewise we've also got a second electron affinity step as well because we're producing an O 2 minus iron okay we're not just producing like late before where we looked at CL minus and that was it we just needed to add one electron with this one we have to add two electrons okay now this process is also endothermic that's strange because you've got a first electron affinity is is exothermic but the second electron affinity is endothermic and can you think why I can ever think well this is because Energy's needed okay you have you're trying to add remember what I said last time you have an electron that you're trying to add to an atom that electron oxygen really does want that electron okay because it's got a shortage of electrons so it's going to really take that electron and for the first electron affinity so that's gonna be exothermic it's more than happy to take it however when you're trying to rather and earned another electron to something that's already negative because you've already got no - it's not so keen because you've got electron repulsion you've got - you trying to put two negative charges together that isn't favorable so that's it's not massively under thermic but it's a little bit endothermic you need to kind of give it a little bit of an incentive a little bit of a little bit of a push to take that second electron and form OT - okay so you've got repulsive forces and this is electron-electron repulsion effects really between the electron and the negative iron so just watch out for that but you know it's easy to spot that'll only happen if you're adding two electrons to the same atom okay so enthalpy change of solution so this is going to be quite important because we make solutions all the time okay that is fundamental in chemistry and yes there's an any change when you form a solution so and this is what we call enthalpy change a solution and this is when one mole of an ionic substance and you do need to know this one as well one mole of an ionic substance is dissolved in the minimum amount of solvent to ensure no further enthalpy change is observed upon further dilution so for substance dissolve it must meet our two main criteria so the substance bonds must break okay that's the first thing in this example here they must break that's an endothermic process you need to put heat energy in to break something don't you that's that's that's that's common sense effectively and new bonds are formed between the solvent and the substance so for something to dissolve what happens is the ionic substance breaks apart and it forms new bonds with the solvent that's dissolved and that could be water for example and when it forms them new bonds that's an exothermic process so it's endothermic to break exothermic to form so just remember that okay so let's have a look here so we've got the ionic loft anak lettuce lattice lattice lattice in solid form so there it is there and we've got in this case our solvent is going to be water so there's our water here okay so substance is broken into create free moving iron so that's the first step remember substance bonds must break okay whatever the substance is so this is the first step so the substance is broken into free moving ions when we add it to the water then what happens is the water then surrounds these ions it's almost like trying to break up something that is like massive with loads of different ions and these waters and swarm the individual ions and form individual interactions with them so the bonds formed between ions and water these ions are what we call hydrated so we have hydrated ions here and because effectively they're surrounded by water and this is effectively dissolved we don't have a solid structure anymore we have ions we the ions are still there this is like dissolve in salt and water you don't have solid salt when you dissolve in water and but this is obviously the the point where it becomes saturated you can't just keep adding loads of salt eventually it becomes saturated but this is why we're saying the enthalpy change when one mole of an ionic substance is dissolved in the minimum amount of solvent in other words at saturation okay so most ionic compounds dissolve in polar solvents like water and this is because the government delegate on the hydrogen is attracted to the negative ions there it is and the Delta negative on the oxygen is attracted to the positive ions and the structure breaks down so waters are really powerful solvent when you think to break structure using heat like egg is the salt and pan again is really difficult but water has this immense power to break up a structure which takes an immense amount of heat to break that's mind-blowing that in my mind anyway and so the water molecules they surround the ions we call that hydration remember that because we're going to come on to that in a moment um and what happens is new bonds formed okay and these new bonds formed must be the same strength or greater than those that are broken okay that's an important criteria if they're not then the substance is unlikely to dissolve okay soluble substances tend to have exothermic enthalpies for that reason okay so when you dissolve something generally have an exothermic process that's that's happening overall and but this is why some substances are soluble and some aren't for example and you have substances which may be massively insoluble if you you know or they are partially soluble they don't dissolve very well and some that don't so this is quite important okay so this is where we're going to use the enthalpy change of solution I want you to remember that structure so if I just go back I want it to remember that process there and because we're going to use this and just have that in your mind and visualize that in your mind as we go through these structures here that's really important okay so what we're gonna do is we're going to calculate it so we're going to take these process here in calculators so we've gone so the enthalpy change of solution okay this is one of the parts that we need to know can be calculated by using the lattice dissociation enthalpy and the enthalpy of hydration so we seen that word hydration previously so we can use a cycle to help work this out okay and you've got to remember how this is structured okay so you got to remember we've got lithium chloride here there it is so lifting applied and forming Li plus aqueous and CR minus a Chris so this is what we call the enthalpy of solution and this is what we're going to try and work out so this is but as similar to it has a cycle so the first thing we need to do is we need to break that up so remember that diagram so it started with our salt here solid compound we're gonna go through and dissociation which basically means we're breaking the ions up no what is involved here technically which is breaking a lot so how much energy does it require to dissociate there ions that's a lie + CL - gasps okay and then enthalpy of hydration so this is where the water then forms an interaction with the ions okay so we're breaking or going via a two-step process so the enthalpy of hydration is when one mole of aqueous ions is made from one mole of gaseous ions okay so this is the process here so effectively it's breaking up then forming bonds with with the individual ions and this these two processes here combined equals the enthalpy of solution okay so we have the same the same well the sum of them - it gives you the enthalpy of solution so we assume that we do the following like we say you break the solid lattice into its gas designs first that's lattice dissociation and then we dissolve their mines in water so this is the entropy of hydration and so remember when we're doing this when we go with the owl we keep the sign the same when we go against the arrow we change the sign and you will be given data to work this out so let's have a look so here this is going to be plus eight four six because we're going with the arrow this is like the again the the journey to Newcastle and go to Newcastle quite a lot and so let's let the journey in Newcastle we need to work out this bit here can't go this way because this is the one we want to work out so it's like a roadblock so we must go here take a diversion to get to the same place so we're going with the arrow here plus 846 and then we're going with the hour here again which is we've got two different steps here so we've got minus five one nine for lithium and minus 3 6 4 for CL minus so the total is minus 8 8 3 and you will be given these data this data and you exam so don't worry about it and so therefore what we do is we work out what the enthalpy of solution is which is minus 37 kilojoules per mole so we do plus minus and that gives us the total amount so this is negative it's slightly exothermic which is what we've kind of expect as well ok so let's look at the enthalpy change of hydration so there are two things that can affect the enthalpy change of hydration that's charge and the size of the iron okay so this is kind of going back a little bit to what we're mentioning before so eyes with a higher charge these attract water molecules much more strongly so this is the interaction remember between water molecules and the ions so these attract them much more strongly more energies released when the bond is MS which means they have a more exothermic enthalpy of hydration the larger the charge greater the enthalpy of hydration okay so if something's got a like a dead calcium for example calcium 2 plus and na 1 plus calcium is going to have a larger entity of hydration than sodium the size of the ion has an impact as well smaller ions have a charged higher charge density than larger iron so ions which are much smaller with the same charge there's more of a charge per square area let's say square millimetre nano meter or whatever it is and so they attract water molecules more strongly and hence there's a more exothermic enthalpy of hydration here so the smaller the iron the greater the end to be of hydration okay very similar to what we looked up before with ions forming an ionic compound this is an interaction between water and the individual ions okay so what we've got here we've got a diagram on here just showing some of these ions so the diagram the Left shows that there shows that there are smaller and have larger charge ions are small out of a larger charge have a higher charge density okay so and there's a stronger interaction so here you can see yeah we've got a two plus charge and a one plus charge this is smaller this is bigger so yeah there's a stronger interaction with water here than there is with the one plus charge okay so you've got a bigger exothermic reaction going on here okay very similar to laser from the ionic one the ionic form in the the ionic structure before okay and that's it so and that was a look at lattice enthalpy for OCR and like I said there's a full range of videos on Alawis chemistry for all exam board specific as well all tailored for your particular exam board and the wall for free there's no charge for them all I ask is that you subscribe to the channel that would be a massive massive help just to show you support and these like say these slides are available to purchase if you want your own personal copy of them click on the link in the description box you get a hold of them there and but other than that I hope you found that helpful that's it bye bye