hello bobcats in today's uh lex um video we're going to discuss transferring energy now remember thermochemistry is the study of the transfer of energy during physical and chemical processes so we are going to now discuss transferring energy as part of thermochemistry what's involved in transferring energy okay so there are two ways that energy can there are two ways that energy can be transferred uh into or out of a system okay the first way is work so let's talk about work um there's two definitions of work i'm going to use well one definition but two equations so first let's talk about um work we said that uh work is one way that tran energy can be transferred so work is with the w and is defined as energy transferred when a force moves an object a certain distance okay now work is very much related to energy and let me explain this hopefully i can do this on um this video real quick so let's use this pin let's say the pin is has no energy relative to the it's sitting on the desk if i apply a force and move it now i have moved it a certain distance above the table that's the amount of work that i've done well that amount of work is also equal to the amount of potential energy that this pin has at this distance above the desk when i let it go it drops and it moves it changes to kinetic energy so the amount of work that i do is the amount of potential energy that i'll have which then is converted to the kinetic energy as it falls and they are all interchangeable and equal to each other now the equation for work so work is equal to force times distance that's the equation we use in physics now let's look at the units for this okay now remember the unit for work we said is going to be a joule and force is a newton times distance which is a meter okay so this is uh the unit of a joule is equal to a newton times a meter but the newton is also a derived unit so we kind of have to break that down so if i look at it the joule is equal to now newton force is mass times acceleration so mass is that acceleration is meters per second squared and then times a meter so this is also meter times meter this is also a kilogram meter squared per second squared which is the same unit that we saw when we did potential and kinetic energy now in chemistry the work equation that we use in chemistry is what's known as a pressure volume work equation so in chemistry we look at work is equal to negative pressure times the change in volume okay now this um equation also will have units that work out um let me get a different pin that one was running out and i apologize i've got really bad allergies today so i keep sniffing sniffling but uh pressure if we look at the units for this one let's make sure the units work out so pressure okay remember we're looking at work is a joule pressure is a is really a newton per area force per area or newton over meter squared and volume remember any volume would be like meters cubed okay so when we do this remember that we'll cancel that and so it's a newton times a meter remember a newton meter so that all comes out to be a kilogram meter squared over second squared so it comes out with the same units it's just that we use uh pressure and change in volume for work when we're talking about chemistry now there is an important thing here there's a unit conversion for this let me put in red so you'll see that the unit conversion for work pressure let's write it here is a pressure volume unit conversion okay so 1 liter times 1 liter atmosphere is equal to 101.325 [Music] joules so we have a unit conversion i know you say wait wait a minute did i just show you that this these units work out the same way and yes it does because pressure is uh force over area and volume is uh distance cubed but remember most of the time we use liters and atmospheres liters for volume and atmospheres for pressure so an easy conversion would be a 1 liter atmosphere is 101.325 joules again excuse me for sniffling my allergies are really bad today now so we can transfer energy through work and we can transfer energy through what we call heat so the other way to transfer energy is heat and heat is represented with a cube and is the energy transferred from a hotter object to a colder one from an object of higher temperature which is hotter to an object or substance of lower temperature it's always always from high to low you don't ever go backwards you don't go from low to high you always go high to low and what's important is to be able to discuss this in molecular terms so let's see what that means so do you need to be able to discuss in terms of faster moving molecules remember the faster the moving the molecule that's moving the higher the temperature that's recorded so faster moving molecules colliding with slower moving molecules or lower temperature oops moving molecules and transferring energy until a thermal equilibrium is met okay and what i mean by this is to be able to think of this so if i have a really fast moving molecule and it collides with a and it so you got a fast moving molecule here and a slow one here and the fast one collides with this the slow one it transfers some of its energy and you wouldn't understand that as it when it hits the slow one moves faster and the fast one moves slower except because it transferred energy but the energy before and after is always the same and eventually after they hit each other enough they get to the same they end up with the same amount of kinetic energy or velocity and we call that thermal equilibrium or the same temperature again remember it's always high too low always high to low now we need to talk about internal energy and energy leaving and entering a system so here's the two ways we can transfer energy now let's talk about internal energy and how we use that to determine if something's transferred into us energy is transferred into or away from its system so let's do internal energy represented with a capital e and i'm going to go ahead and show you or it could also be represented with a capital u and i think in engineering they use a u in chemistry using e but um your book uses you almost every other book i know uses e but i'll put them both up here so if you see them you'll know that they're both interchangeable for internal energy and internal energy is the sum of all of the kinetic and potential energies in a system okay now usually we do not discuss internal energy itself it's very very difficult to come up with a value for if i were looking at my desk right here all these molecules in this desk are moving they have some kinetic energy because they're under vibration but they also have a lot of potential energy because they're bonded to each other there's a lot of attraction and we know that because if i start the if i take the desk and i start it on fire it's going to continue to burn or release energy so there's a lot of potential energy here but there's also kinetic but it's hard to know or calculate or put a numerical value to a system's internal energy so what we really look at is the change in energy of a system so i'm going to write this so really we want to look at delta e is equal to energy final minus energy initial and we're really wanting to deal with this and you can think of this also as since this is uh the final energy that would be the energy of the products minus the energy of the reactants okay now this is the first law of thermodynamics so i'm going to write that out now we said that the first law really is stated as energy cannot be destroyed created or destroyed only transformed from one form to another so but i'm going to state it in a different format here but it's the same thing so the first law of thermodynamics is a change in energy of a system must be accompanied by an equal and opposite change that's an i sorry opposite couldn't spell very well there opposite change of energy in the surroundings because the energy cannot be created or destroyed it just goes from one form to another so there's got to be equal and opposite energy of the surroundings as there was lost in the system now in the equation wise what that looks like is this it would look like we would say the change trying to get different color the change of internal energy of the system is equal to a negative change in the energy of the surroundings okay and that's really the first law of thermodynamics now so how does that look let's go through this and look at a system and how does that work so if i have let's put a square and make the square of the system and then everything outside that square is the surroundings and we have energy leaving the system and going to the surroundings leaving the system and going surroundings you might think of it as this let's look at it in this format let's say i have um this is energy increasing going up okay and let's say i start out with my initial energy and then i have my final okay and so as i lose energy this direction i have to release that energy so as i go down at energy that from a high to a low energy's got to go somewhere and so we have to release that energy from the system okay so in this case we are looking at energy of the system is going to the surroundings equal and opposite okay and in this case the energy the final energy is going to be less than the initial energy okay and so if i take final minus initial remember this up here is final minus initial then my delta e is going to be less than zero which means it's negative in value and we call that exergonic if we're just talking about energy it's exergonic if we're talking about heat energy it's going to be exothermic and we'll get to back to that in a minute so as energy leaves the surrounding is going down in energy and because the surrounding is going down in energy um it's a it's going to be less than zero or negative it's going to be negative it's going down it's losing energy so it's negative exergonic and the other one is let's look at the surroundings so here's my system the outside of the system is the surroundings and here we have energy entering the system so energy is going into the system okay and so again another analogy if we look at this with energy increasing as you go up let's say our initial energy now is low so the initial energy of the system and remember is low and we add energy to it so the final energy is higher than the initial so we have to go up in energy and that means you have to absorb energy to go up so energy is absorbed and in this case the energy is going from the surroundings into the system okay and so now the system is increasing in energy and now my final energy is greater than the initial energy of the system and so the change in energy is greater than zero or positive so it's a positive value and we call it exergonic or endergonic sorry ender conic and the way i remember is that energy is entering we're going into and so endo sounds like it's going in okay so that's the first law of thermodynamics in that we have energy going into the system or out of the system but whatever change in injury the system has to be equal and opposite to the change of energy of the surroundings and then there's uh values over here that we can see positive and negative values so let's go back to this idea of transfer of energy so um let me let me make this statement here i should put it on here real quick one last thing to say so the internal energy of a system remember we want to look at the systems i think though in engineering you look at the surroundings but in chemistry we look at it through the system can be changed okay so remember we can do that by we can change the amount of energy in a system by a flow of work heat or both okay and so there's an equation that's really important to go with this one this this is the equation you really need to know is that the change in energy in a system is equal to the heat plus the work done on the system okay so you need to know this i'm going to put a star right next to it okay even though it's last one on this page it's still very important okay now so let's talk about how that work and heat flow affects our system now just a reminder this is really important thermo dynamic or thermo chemistry dynamic quantities always consists of two parts and you make sure if you miss a part you get it wrong you have to have both parts so two parts first is a number or value giving the magnitude of change and then the second part is a sign positive or negative indicating direction of flow in or out of the system okay now also you need to use your units joules but um we want to make sure you know that there's got to be a sign with i i had a lot of trouble in thermodynamics and when i was in college because i kept forgetting to put the correct sign and by the way the sign reflects the system the system's point of view okay now so energy into the system repeat just repeat this again it's so important to understand this kind of stuff um energy into the system is positive sign remember you're increasing the amount of energy so you're going up in injury it's a positive sign energy out of the system is negative because it's going down in energy you're losing energy so it's negative okay very important for you understand and just as we had the first law of thermodynamics saying that the energy the the internal energy of a system is equal to the negative internal energy of the surroundings we do the same thing so the heat of the system is always equal to a negative heat of the surroundings or we can say the work of the system is equal to a negative work on the surroundings okay obeying the first law of thermodynamics so let's go through this heat flows let's look look at heat and then work so one if heat flows out of system so let's look at it as heat flows out of system flows out of system um so we have a negative q and it means system loses energy and we would say that this is exothermic because it's heat right not exogonic but exothermic now um one important thing to think of is that the surrounding gains energy and therefore the surroundings are warmer that's why exothermic reactions um give off heat because they're actually the the reaction itself is losing the energy and the surroundings which is everything else including you and me um is getting warmer because we the the surroundings is gaining the energy that was lost by the system okay number two heat flows into system okay so in this case we have a positive q and it means system gains energy and so if it's gaining energy it's absorbing or endothermic the system is absorbing the energy it's becoming endothermic and in this case the surroundings loses energy loses energy and therefore is cooler remember these three dots like this is therefore shorthand for therefore okay now we need to look at work so number three work done by system on surroundings work done by system and then just on surroundings now again i'm going to use a piston idea because that's where the pressure volume work comes from in chemistry so if i have a piston like this and then in that piston there's solid form now if we have a negative work negative work negative work means energy is transferred to surroundings by doing work okay and think about it if we have in a system and in the system if you do work in other words if the piston moves up the system is doing the work and it's losing energy to the surroundings by doing work and usually we can think of this as expansion okay so i have i do some i have a reaction that goes on that creates a pressure but we have to keep the pressure constant so the volume changes and increases and as it increases work is being done by the system and therefore it's a negative w because it's losing energy to the the surroundings okay and then i don't have room on this page so i'll go to the another page to talk about work done on system and then we're going to do a quick um a table and a practice problem so uh four work done on system by the surroundings okay now let's do the piston again here's my system and in this case work is being done on by the surroundings on the system so the piston goes down but it's the surroundings that are doing the work on the system and so we get a positive w meaning energy is transferred to the system by work being done on system by work being done by surroundings now think about it remember when if i push this in we're going to add energy into this uh system just like if i when i picked this pin up i'm adding energy potential energy into my system which is the pin now which is above so i've done work on the pin and now it has gained energy potential energy just like this work is done on a system so the system gains energy you can think of this as compression and compression is a result of work done on system okay and that's how our combustion engines work it's how we get our cars to do what they need to do because we're either doing work by the system or on the system and our system would be a piston so let's look at a table real quick of what these would look like so remember if we have q plus w equals delta e or the change in energy and let's say we have a positive q what's positive q positive is work done or heat flowing out into the system so if we have heat flowing into the system and work done on the system then we have a positive delta e if we have workflow heat flowing into the system and work done by the system it all depends on your values and then if we have work and heat flowing out of the system and work done on the system then it's also depends on q and w values meaning that if this is a higher value than this then it's going to be a positive delta e or if the work of the heat lost by the system is higher than the work done on the system then it's a negative delta e and then if you have negative for each of these then you know that delta e is negative and so this would be exothermic and this would be endothermic okay now let's do a practice problem make sure everybody has that down okay a reaction occurring in a flask releases 890 joules of heat two surroundings and the gas produce the gas that is produced performs 450 joules of work on the surroundings okay by pushing a piston by pushing the piston upwards okay i try to do the best i can to draw this um so it's kind of like if i have my piston here and it's connected to a flask here and then i'm going to just draw a line so this is the flask down here we have the piston and you have an initial volume here so my initial volume and then we have a piston the same piston again the this is the flask here that i'm trying to show you i'm not going to draw a flask because i'm not too good at it but it's it's connected to a flask and then this is where the piston ends up so that's a final volume okay so first we need to a is this a closed open or isolated system uh and why explain b determine the signs of q and w in this reaction of heat and work in reaction and c determine the change of in energy determine change in energy or the delta e for reaction okay so first thing is is it an open or closed system so when i look at this it's not open it's closed because the flask that i'm not showing is a closed flask and this is just a tube that that takes it to the to the m um piston if you want to look at it i got it drawn right here so there's it looks like this so we know it's closed so we say that this is a closed system and explaining that so this is a closed system because energy but not matter can flow between system and surrounding [Music] kelly can i call back i'm making a video real quick oh i'm so sorry that's okay love you bye sorry about that um my wife just called i should have had the phone turned off and i forgot to turn it off so i apologize for that interruption but we're almost done b so for b we need to find out if q is a positive or negative so let's say energy energy is released from system therefore it's a positive no it's negative q negative q energy is released from system to surrounding so it's negative q and then in this case work is done by system and so also energy is going from the system to the surroundings because work is done by the system so this is a negative w and then the last is c where delta e is equal to q plus w so delta e is equal to and in this case remember energy was uh the heat was 890 joules and the work was 450 so it's a negative 8 90 joules plus a negative 450 joules so the delta e is a negative 13 40 joules of energy and we really like to say that the delta e is a negative 1.34 kilojoules of energy okay so that's how we look at what's going on with energy we can either uh transfer energy through work i mean work here w or heat and our next video is all about just the heat we're going to forget about the work and i'll see you in the next video thank you