 Hi, I'm Zor. Welcome to Unizor education. I would like to continue talking about chemical energy Primarily the energy which is inside the molecules the energy which basically is attributed to the bonds between the atoms which Basically are the components of any molecule Now this lecture is part of the course physics for teens part of the Website Unizor.com It's a free educational website where I also have the prerequisite course math for teens Mathematics as you understand is the foundation Which is absolutely necessary to learn physics. So I do suggest you to take or at least familiarize yourself with the math for teens course All the topics especially the calculus which will be definitely needed for all the aspects of our physics course Okay, so Chemical energy Let's just start from from the beginning of this course. We were talking about Mechanical energy first now what is mechanical energy is energy of objects as they are moving or positioned Somewhere relative to other objects. So it's basically an energy Which is attributed to objects as we know them like this marker or something like this the next Topic within the energy Part of the of this course was about Thermal energy the heat now the heat is Energy of the molecules inside of any object and the molecules are actually the smallest Components of any object of any substance rather which maintain the same Properties as the substance itself. So there is something which is called the molecule of water Which is water anything less smaller than the molecule of water is no longer be water So now the chemical energy is Even deeper. So first we went from mechanical energy of the objects down to Thermal energy of the molecules inside the objects, but the molecules are still of the same substance Now we are going inside the molecules to talk about the chemical energy All right, so basically the chemical energy is somehow Inside the molecules. So we have to talk about what actual molecule is well There are certain components of every molecule now the total number of different molecules the total number of types of molecules is extremely large obviously we have molecules of water We have molecules of protein. We have molecules of this and that and that hundreds thousands millions of different types of molecules however, but it's very interesting there is a relatively limited relatively small number of smaller components From which the molecules are made now these smaller components are called atoms and There are about a hundred different types of atoms They are all collected into a table called periodic table of elements developed primarily by Dmitry Mendelev the very important scientist who lived I Think it was like 19th century in in the in Russia So anyway, this periodic table of elements lists all the different types of Elements from which molecules are created Now what is an example of more? elementary Particle or whatever Than the molecule so what are these little bricks 100 or actually 103 right now, I believe of different types of Atoms from which the molecules are are built. So what are in this periodic table of elements? well the elements where grouping to different groups based on their Properties, etc. But in any case there are only about a hundred of them and from different combination of these atoms in different numbers The molecules are created So let me just give an example of a particular element. Let's take iron iron is molecule of iron is Created by one atom of Element called iron So the name is the same, but the molecule of iron is not exactly the same as atom of Iron of element iron So one is considered the molecules considered with their physical properties, etc. The atom has its own in inner structure, which we will talk about a little bit later But anyway, let's just think about these two different things because it helps in other cases when the molecules are more complex So what's more complex molecule the molecule which contains two atoms, right? So there is a molecule called molecule of oxygen and It contains two atoms of Oxygen now in this case if we have two atoms unless they are connected to each other through some kind of a bonding They will not be able to form a molecule So whenever we are talking about oxygen as we are just picking it from the air one molecule of oxygen That's two atoms bonded together by inner Connection in their bonds the forces which are acting between two atoms of oxygen They are connected to each other and make up a molecule of oxygen, right? So this is The molecule of oxygen and it has one bond Now in this particular lecture, I will Exemplify this concept of energy which is inside the bonds because that's exactly what we wanted to talk about in this lecture The energy the chemical energy, which is basically the energy of these bonds We will talk about the gas called methane and that's the formula, which is basically One atom of carbon Connected to some kind of bonding with four atoms of hydrogen So this is a molecule these are bonds which we are talking about and Again the chemical energy inside of this gas methane is the energy of these bonds We have to somehow Investigate what what what is this energy? What is the energy inside the atoms the atomic bonds and? This is the subject of this lecture So first we have to define basically what is The chemical energy of the bonds. Well, this is a potential energy Because right now the molecule is basically as a whole it's intact Right, so it's the same thing as solar system now the solar system is something which basically exists more or less intact and there is a potential energy of the movement of every planet there is a potential energy of Gravitation Relative to Sun etc. So if we want to change it somehow We have to change this energy. We have to change the Movements of planets. We have to move them forward or backwards further from the Sun and closer to the Sun Anyway, whatever whatever the existing Mechanisms which hold this particular solar system together if we want to change it We have to break something right so there is something like a potential energy of the system This is exactly the same thing. There is a potential energy of all the bonds in between the atoms Which comprise the molecule which we have to break to release this potential energy So chemical energy is a potential energy of the bonds Which hold the molecule? Together, it's inter atomic bonds and only because these bonds exist The molecule actually can be Can't can exist Okay, fine, so we have defined the chemical energy is a potential energy of The bonds between the atoms that comprise this particular molecule now How can we use this energy? How can we actually release this energy? Well, as I was just talking about solar system if we want to you know to release something Which is inside the solar system the energy we have to break somehow and rearrange it Same thing with chemical reaction chemical reaction is the way to Break some molecules and create other molecules. So any chemical reaction Changes the chemical composition. You have one substance which contains some some kind of molecules another substance Which has another kind of Molecules you combine them together may be apply certain conditions like heat pressure whatever else and then the chemical reaction Starts and what is a chemical reaction? Well the atoms from one molecule and from another molecule somehow are Separated from from the holes from the molecules. So the bonds are broken and then the new bonds are created Now this is a very complicated mechanism. However, we can represent it in the way of some kind of a formula chemical formula and This will basically tells you what exactly is happening now. What happens? when you turn on the gas and start Light it up if you have a regular kitchen stove Well, the gas coming from the pipe is methane now what happens with methane? When it burns well, here is what happens it combines with oxygen from the From the air and as a result Let me take another marker and as a result We have something else Now, what do we have? Well, we have Carbon dioxide and We have water vapors So this is water. This is carbon dioxide. This is oxygen and this is methane Well, now this is supposed to be like a formula like an algebraic equation. So Parts should be equal now. How many atoms of hydrogen for instance to Here we have four So that's not a real equation now. What is a real equation? Well, we have to really equalize now We have to put two here To make the number of hydrogen equal C is one here and here oxygen is two and One times two which is two so it's four. So we need to To get two atoms of oxygen, right? And now we can put an equal sign here So this is the chemical reaction which happens when you are Cooking so the methane The one molecule of methane actually like put it this way each molecule of methane is somehow reacts it Absorbs somehow in this chemical reaction two molecules of oxygen and as a result we have Carbon dioxide and two molecules of water Now we know that when you are Burning methane there is some heat generated. So there is energy generated now where this energy is coming from Well, the energy is coming from The chemical energy inside these molecules and that's what's very important. That's what exactly what's happening here These bonds within these molecules are Destroying are destroyed somehow and the new bonds are Actually formed and as a result of this Certain energy gets freed basically Okay, so let's just Count basically how can we count amount of energy here and here? Well, we have to break the bonds, right? We have to break these bonds and Have the result and we have to break these bonds and have the result and we will compare now if the Result will be not equal and result will not be equal whatever the difference is is the amount of heat which we will produce by Burning the methane right Now how can we experimentally probably determine this fact? Well, we have to take one molecule of methane two molecules of oxygen Combine them let them burn somehow and See what exactly the result of amount of heat actually is produced Huh, we can't really do this experiment with one molecule, right? Okay, so what I will say is okay. Let's take Proportional number of proportional number of like for each molecule of methane. We will take two molecules of oxygen Well, how can we do that? Not easy, right? I mean we can measure the weight for instance or mass Of the gas we can do that However, how can I compare how much grams of this I had I have to take? to and and this To to make this ratio of the molecules one to two Okay, now for this we have to go even deeper into the atom. So first we went from Objects to molecules from molecules to atoms now we go deeper into the atoms now the all Universe of different substances is created as we were talking about from about a hundred Different elements types of atoms, right? Which are in periodic table of elements of Mandelaev Now what is the atom? consists of well for the purpose of this course We will build the Model of atom as it was basically more or less Agreed by all the physicists And we will completely ignore Everything which is not as substantial and not contributing to whatever I would like to talk about So for our purposes we can view the atom as containing certain nucleus surrounded by electrons on The orbits around this nucleus nucleus in its turn contains two types of particles protons and neutrons, so we have protons We have neutrons and we have electrons. I Mean, I'm sure you've heard these names, but let me just well Repeat it if you know it so protons and neutrons somehow There are some bonds between them and They form nucleus certain number of protons and certain number of neutrons. They're combined together Into a nucleus now electrons are Surrounding on different orbits and earth like circulating around the neutrons around the nucleus It's not an exact model. It's not what actually is happening in in in the real world Well, quite frankly, I'm not sure anybody knows how which is exactly but the model is good enough for purposes and and certain experiments whatever we are doing that seems to correspond the model corresponds Well, the behavior of the model corresponds to behavior of the real things to a certain degree certain approximation Okay, now protons are electrically positive charged neutrons Neutrons are neutral. That's why they're called neutrons and electrons are electric electrically negatively charged so electrons are circulating and this electrical Attraction between positive and negative holds them on the orbit Now electrons are very very light So light that we will for our purposes we will ignore their mass now protons and neutrons are much heavier significantly much heavier and they actually Contributes the lines portion of the mass of the atom Now they are more or less of the same mass more or less and we call this mass of the proton or a neutron atomic Weight unit atomic weight unit. So atomic or mass unit rather atomic mass unit. I would say so the Atomic mass unit of proton or neutron is considered to be one Okay now Let me just go again Any substance and there are millions of them So millions of types of molecules only 100 types of atoms and Each atom contains in for our purposes three types of different particles protons neutrons and electrons So atoms in their different configuration These 100 types of atoms in different quantities and different combination Make up millions of different substances now three types of elementary particles are Making a hundred different atoms represented in the periodic Table of elements so from millions of Molecules types of molecules we have hundred about a hundred hundred and three types of atoms and each atom is Consists of only three types of different particles. So in different quantities These three make up any element Okay That's quite an interesting way. You see we are simply we're simplifying the universe we are trying to build our universe which is extremely complex from a component from components and Each component can be built from even more elementary components, right? So that that's it's like the car and there are many many many different types of cars, right? But they contain only certain Number of engine types, right? And then every engine contains only certain number of parts from which this engine actually Contains inside. So that's our Gradual simplification of the universe to build The whole picture of how the world actually is is made up Okay Now if we know What exactly each elements each atoms composition as far as protons neutrons and electrons? We can make a judgment about the weight of the atom so and We know using certain electrical magnetic whatever other proportions whatever other properties About different elements we know actually what is the composition of each element in the periodic Table of elements of mint delay. So there are 100 and three elements right now and for each element we know What's the composition? How many protons how many neutrons and how many electrons? Well, a number of electrons usually is the same as number of protons because this is positive This is negative. So they should be neutral Otherwise, we will lose electrons or we will maybe consume some electrons from From from the other side it will not be neutral anymore But Adam is supposed to be neutral and to make it neutral We have to have the same number of protons and electrons Neutrons can be different in many cases the number of neutrons is Little less than number of protons a little more than number of protons or equal to the number of protons Now why the world is created this way? Nobody knows but we don't care right now It's created this way and we know about this particular Model of the world which kind of gives us the good impression of how basically the universe is created Now so what do we know? We know the internal structure of the hydrogen hydrogen contains one proton and one electron Which is Surrounding which is circulating around this proton now if it's a one proton its atomic Mass is one we have agreed that proton each proton and each neutron has Approximately mass of one actually it's one point zero zero zero or something etc But for our purposes we assume it's one so that means that hydrogen Has atomic west atomic mass of one now similar consideration We have carbon It's 12 It's a certain number of protons certain number of electrons And certain number of neutrons, but basically that's what makes the carbon. I think it's four protons and four electrons and eight Neutrons, but I'm not sure now Oxygen Is 16 so there are 16 protons and neutrons together. I think it's eight and eight Maybe not. I don't remember again What else is here? nothing so from these We can actually calculate the atomic weights of each element which we're Using here, right? So let's just do it this way So this would be 12 plus four times one right Each H is one carbon is 12 now. This is two times 16 times two right or to Mean 16 plus 16 and these two because we have two molecules now this is 12 plus two times 16 This is molecule and this is two times H2 is two times one and times 16 So what's the result? 16 and 64 80 Here we have 12 and 32 that's 44 and the molecule of water is 2 18 plus 36 right to put two times 18 36 And that's also 80. Well, no wonder we have an equation 80 and 80 because mass is the same We are just rearranging the atoms, but it's exactly the same atom one atom of Carbon here one atom here four atoms of hydrogen here two and two here two times two that's four and We have four atoms of Oxygen two and two four so obviously mass is supposed to be the same Okay, now how about the energy Now this is much more complex you see to To evaluate the energy we have to break certain atomic bonds, right? now The theory behind what is exactly atomic bond is Complex and is beyond the scope of this course, however, what I can do I Can actually use certain? Known facts which have been established by the theory and corresponding experiment and I can tell you the following so what is molecule of Methane It's four bonds between atom of Carbon and four atoms of Hydrogen and it has been established that each bond is 410 kilo joule per mole and I have used a new word mole here is very important thing Now we were talking about some experiments where we have to take one molecule of this to molecule of that Then we will get molecule of this and two molecules of that We can't really experiment with molecules now, however now using the atomic weights We can make certain amount of methane and certain amount of Oxygen in such a way that for each molecule of methane we will have two molecules of oxygen how can we do it? well, very simply if molecule of CH2 weighs what 12 plus 4 it's 16 and each molecule of O2 is 16 plus 16 is 32 so we need 64 right so if we will take 16 gram of Methane and 64 gram of oxygen Then the number of molecules here will be exactly twice as much as the number of molecules here, right? If one molecule Ways or has a mass 16 atomic mass units then 16 gram Will Contain certain number of molecules, which is what well it's certain number of molecules, which is proportional to molecular to atomic weight molecular weight using atomic mass of each one so if each one has 16 atomic units Then we have 16 gram now each of these has 32 so whenever we have 64 grams we will have twice as many molecules Since they are just making the weight of the gas proportional to the Weight of one molecule that means that in each 32 gram We will have exactly this 32 gram of oxygen We have exactly the same number of molecules as in 16 grams of this So if we want twice as many we have to just take 64 so my point is that it's very convenient to deal not with molecules of substances but with moles of Substances where mole is the number of gram which is equal to the atomic weight So if atomic weight of this is 16 we will take 16 gram If atomic weight of this if this is heavier for instance Oxygen 32 we will take 32 grams and the number of molecules is basically what it's the weight of The entire amount which we take divided by the weight of one molecule That's the number of molecules. Okay, and the number of molecules will be the same So that's very important that if we will take the amount of any substance in grams Equal to Atomic mass of the corresponding molecule. We will have the same number of molecules, right? so if you have if I have this one weighs let's say a and this some other object weighs B and I will have a Certain weight of this like a million of a and certain Weight of B, which is a million of B that actually means that the number of these items will be a million here in the million here So this is the molecule of Methane this is the molecule of oxygen oxygen this weighs 16 Atomic units this weighs 32 atomic units So 16 gram of this will be the same will have exactly the same number of molecules as 32 gram of this and This amount of substance is called a mole. So a mole of CH4 the mole of methane is 16 gram the mole of oxygen 16 plus 16 32 and this number is Amount of energy to break each bond When you have a mole of this substance So for four of them we have 16 40 for 10 times 4 now for oxygen We have 494 kilojoule Per mole So now we actually have amount of energy needed to break this bond or this bond and again It's really Sophisticated theory what kind of bonds these are and why the amount of energy is such and such etc so knowing this amounts for Any mole we can actually find out amount of energy Which we will release when we will burn Let's say one mole of methane 16 gram of methane Okay, so let's just do similarly in case of CO2 CO2 is this So we have to break two It's 799 each So which means the total will be 799 times 2 So this is also 799 so total will be one five nine eight So this is one connection one bond which we have to break. This is four bonds each for ten This is two bonds each 799 What else we need H2O? Okay, H2O is this So we have to break two bonds And each bond is what 460 so it's 920 together now let's count so we have CH4 which is 1640 plus two molecules of oxygen so it's two times four ninety Four so Let me write it over there. So we have 1640 kilojoules per mole plus two times four ninety four and This is equal to 2628 That's on the left side on the right side We will have By the way in grams that would be what? 32 and 1244 and this would be 216 18 1236 gram So that's our equation in grams, right? So on the right side, we will have one molecule of CO2, which is this one, which is 1598 And two molecules of H2O. So it's two times 920 Which is equal to 34 38 34 38 So this is energy in and this is energy out Or left and right, whatever you call it. You see the difference the difference is 8 10 kilojoules per mole That's amount of energy. We will Get in a form of heat in the form of heat Whenever we are burning 16 grams of methane It will consume 64 gram of oxygen from the air We actually know because if if the air is unlimited supply of oxygen now, this is controlled obviously because it's Given through the pipe So if we will measure 16 gram of CH4 Then burn it. It will consume this much. It will exhaust carbon dioxide into the atmosphere and vapor and 810 kilojoules of energy will be released So that's the calculation of the energy related to atomic bonds Now again one thing which kind of makes me a little uncomfortable I really don't know how they came up with these numbers how to break each bond as I was saying it's kind of a Satisticated theory and experiments together and they came up with these numbers, but these numbers are known So for each connection, we know basically what's the energy of this bond? How much energy is needed to break this bond? And That's actually all I wanted to talk about today so From the theoretical standpoint, I think I have explained everything I wanted about chemical energy I'll probably make a little exam Not very difficult one because it's not really like too much energy it Too much theory behind this energy of the bonds. I mean, I mean there is a lot of theory, but not as much as For this course because the theory the real theory is significantly more complex It goes inside the atoms now what is important is that we were able to Kind of simplify our universe from all the different kinds of substances to little bricks from which these substances basically are Built the molecules now each molecule and there are again millions of different kinds of molecules now but each molecule Contains only about a hundred different elements. I mean no more than a hundred of different elements in different quantities and in different combinations and Now we have simplified millions to a hundred millions of different molecules to a hundred of different atoms now each atom in our simplified again model Approximately right each model each atom contains only three Elementary particles protons neutrons and electrons so that simplifies us even it's even more so from three Elementary particles we have about a hundred different atoms and from a hundred different atoms We have millions of different molecules. That's how the whole pyramid actually is is built. It's all very beautiful and Unfortunately, it's not a hundred percent corresponding to the real life real universe, which is significantly more complex But again for our modeling purposes We are not really Studying how the universe is really created. We are building the model The model has certain behavior which well more or less Approximately corresponds to the way how the universe behaves and then we're studying the model Okay, so that's it for today. Thank you very much and good luck