Chemical Thermodynamics: Enthalpy

So entropy just represents the amount of kinetic energy which is the energy of motion that transfers between our system which represents our chemical reaction and everything else, which is our surroundings. And this is done under constant pressure. Now we're gonna say here that our entropy of formation which is delta H. F. Here. The little circle just means under standard conditions. It represents the heat change between reactant and products that are in their standard or natural states. Now, when we talk about entropy and we accompany it with delta H, we usually refer to two terms XR, thermic and endo thermic processes. Now we're going to say in an excel thermic solution or reaction R. Q and R. Delta H. Are equal to one another under constant pressure. And when we're talking about exo thermic processes, both of them will be negative. Now here in this example we have three moles of hydrogen gas plus one mole of nitrogen gas combined to form two moles of ammonia gas as our product. Now we're going to say here, we're talking about eggs, a thermic processes. We're just releasing heat in order to form bonds. So that's why we can see that we have two reactant here combining to give us one product. Now here, since we're trying to form bonds, we want to make sure that those bonds that we form our strong. So we're gonna say here strong bonds are formed as a result. Now if we form strong bonds for the products, that would mean that our reactive bonds initially would have to be somewhat weak so they can break down and then reform are stronger product bonds. So we're gonna stay here, we're gonna have weak lattice bond energies. So the bonds connecting the hydrogen together, the nitrogen together must be weak so they can break down and reassemble to form NH three at the end. Now here we're releasing heat here, we can say that these black spheres here represent our system or chemical reaction and they are in a solution. So just think about it. The releasing heat as they release heat, they're losing kinetic energy. So they're gonna move much slower. They're gonna move slow enough. Eventually they're gonna come together and form connections, form bonds. Now, as they're releasing this heat, the heat is being absorbed by the water. So that means that if I took my bare hand and I touched this glass which contains the solution, the glass would feel warm to the touch. And that's again because the chemical reactions, fears the black ones are releasing heat. The water is absorbing that heat. The water gets warmer, which means the container that they're in, feels warmer to the touch. To me as well. Now here in indo thermic process is basically the opposite and an endo thermic process. Both our delta H, and delta and Q. Are both positive values here, we have H. B. R. S are reacting that gets separated into its ionic forms when thrown into a solvent like water here in an endo thermic process, we're taking energy in, We're absorbing it in order for us to break bonds. If you could just think of an ice cube, you take an ice cube and you take a match you light that match over the ice underneath the ice cube. The ice cube will eventually absorb that energy in order to melt. Now here we can say that again are black spheres who represent our chemical reaction that's being undertaken here. It's absorbing heat from the surrounding water so that it can break itself free because of its absorbing water from its surroundings. The water when I touch the container is gonna feel cold because all the warmth from the water is being transferred into the system. So an endo thermic process feels cold to the touch. And again we said everything is the opposite. So here we have strong initial bonds here, that's why we need to absorb energy in order to have enough energy to break those bonds. And since we're breaking bonds, we don't want any newer bonds forming for our products. So we'd have weak bonds form. So just remember when we're talking about entropy, we're referring to delta H. Under constant pressure Q. And delta H are the same thing. They represent entropy. They represent heat. Now here, if we're talking about exo thermic and endo thermic processes, remember they are connected to face changes as well. So here, if we're going from a gas to a liquid, we're forming bonds. And if we're going from a liquid to a solid were forming bonds, we can also go straight from a gas to a liquid as well. Each one of these phase changes represents an endo thermic exhaust thermic process. So here gas to liquid would be a condensation reaction liquid to solid represent freezing or you can go straight from gas to solid, which is deposition. Now endo thermic processes. Remember we're breaking bonds by absorbing latent outside energy here. If we're going from a solid to a liquid that represents melting or fusion, if you're going from a liquid to a gas that represents vaporization or evaporation and then finally you can have yourself going from a solid street to a gas which is just sublimation. So again with endo thermic and exo thermic processes, it's going to be important and imperative that you remember these different terms which represent the different types of phase changes that can occur with each of these processes. Now finally we're gonna say in terms of energy diagrams, the layout for thermo chemical equations can be displayed by the images below. So here we have energy diagrams on our Y axis, we have entropy as our label and then here we can say that our X. Access is just the progression of the reaction. Remember in all these reactions were just going from reactions to products, reactions to products. We're gonna say here that our reactant sat are at a higher energy and then our products are at a lower energy. All of these energy diagrams follow the idea that the entropy of our reaction which is our system equals products minus react ints for this first image because our products are lower than our reactant, our delta H. Will be a negative value. Which means that this is an ex ah thermic process. So in an extra thermic process we form products with lower energy meaning they're more stable in the next image. We have the opposite. Our reactant are actually lower in energy and our products are higher. That's because our reactant have absorbed energy to create products with more energetic properties. So here this would be positive and this would be endo thermic. And then finally here we're gonna say that our reactant and products are both the same energy level. So there is no change in the entropy of my reaction. So delta H. U. Would be equal to zero. So that would mean that this is a thermal neutral process, thermal neutral process. Okay so just remember when it comes to envelop, we're really talking about thermal energy and we're talking about how that thermal energy is being transferred between my system which is my chemical reaction and my surroundings which is everything else. Whether my system is gaining or losing energy helps to determine if bonds are formed or broken and helps us determine if the process in itself is XR thermic and endo thermic