Endothermic & Exothermic Reactions - Video Tutorials & Practice Problems

Endothermic & Exothermic Reactions

Now Endo thermic reactions involve absorbing thermal energy by the system from the surroundings. And we're gonna say here as a result of absorbing this thermal energy, the molecules will start to speed up and if they're given enough energy, they can use it to break their bonds. So endo thermic reactions are heat absorbing bond breaking reactions here, we take a look if we look at it in terms of phase changes. If you're absorbing heat, it helps to spread molecules apart. Think about you have a solid here, the solid absorbs enough heat, thermal energy. Think of it as an ice cube. What happens to the ice cube? Over time? It melts. Now it's a liquid. Let's keep adding a little bit more heat to that liquid water. What happens to it eventually it vaporizes into a gas here, We're breaking the connections between water molecules as it goes from solid liquid to gas. Now, if you're going from a solid to a liquid that is melting or what we call fusion. In terms of thermal chemistry, if you're going from a liquid to a gas that's vaporization and then if you're going from a solid to a gas that's called sublimation. Now, real world applications, if you are an endo thermic reaction, you're absorbing heat from the surroundings. Now, if I were to touch an endo thermic reaction that's contained within a container, what would it do? Well, it would absorb heat from my hand. So the the substance is absorbing heat from my hand. So it feels cold to me because I'm losing heat from my hand to the container. Finally, in terms of an energy diagram, energy diagrams our way of showing how a reaction progresses. In terms of energy, you start off as a reactant to get to your final product as your last stop. In an endo thermic reaction, your entropy value, which is delta H, is positive, it's a positive sign here. The beginning part of this energy diagram is represented as our reactant and then here's where you end. This represents our products, here are y axis is energy. So in an endo thermic reaction are react and start off at a lower energy and our products and at a higher energy. This gives us a positive entropy or delta H.

Endothermic & Exothermic Reactions Example 1

here. It says which of the following processes represents an Indo thermic reaction. Remember, India? Thermic reactions are heat absorbing bond breaking reactions. So here we have steam condensing If you're condensing, you're going from a gas to a liquid here. You're not breaking bonds, you're forming them. So this is out next. Molten lava Solidifying. Solidifying means you're going from a liquid to a solid again. You're not breaking bonds. Okay? Water boiling If you're boiling, that means you're vaporizing your liquid water into a gas. You're breaking bonds here. So this is Endo thermic and then finally, we have water freezing. If you're freezing, you're going from the liquid. Phase two the actually going from Yes, the liquid phase to the solid phase here, not breaking bonds. You're forming them. So this would not be Indo thermic. So, out of all the options, only options C represents an Indo thermic reaction

Endothermic & Exothermic Reactions

exo thermic reactions involve releasing thermal energy by the system to the surroundings. Now we're gonna say as molecules in our system release heat, they slow down and with enough energy loss, they form bonds. So exotic reactions are heat releasing bond forming reactions. We're gonna say in terms of face changes, let's think of it as energetic gas molecules as we release heat. Those water molecules they're gonna come closer together. So think of liquid gasses, water bouncing all over the place in a container. They slowly start to release their heat and they slow down because they're losing energy. If they slow down enough, they condense into a liquid. So this is condensation. If the liquid water that we've collected, we put it in the freezer, they will continue to lose heat and they will solidify. So liquid to solid is freezing some substances under right conditions. They can skip the liquid phase altogether. One example is carbon dioxide, we call it dry ice. You could take it out of a very cold container where it's in its gaseous phase and put it outside. It'll skip the liquid phase altogether. So if you're going from a gas to if you're going from a gas to a solid though where we're taking that gaseous um carbon dioxide and putting it back into the container where it solidifies again, that's called deposition. Now let's think about it, let's say container has a liquid and that liquid is an Excel thermic reaction. It's exo thermic so it'll be releasing heat. So if I were to touch that container, I would feel the heat that it's releasing to my hand. So X. Academic reactions feel warm to the touch Now if we don't think of it in terms of an energy diagram in an energy diagram, our Y axis is our energy and then X axis is the progress of the reaction. Remember the whole point of a chemical reactions to go from react inTS two products. And what we need to realize is that in an XR thermic reaction the reactions have more energy. They release their excess energy and they dropped down to become products. Over time the products have less energy because we're releasing energy to go from reacting to product. Our entropy delta H. Would have a negative sign. So just remember this is the way we depict an X. A. Thermic reaction in terms of an energy diagram.

Endothermic & Exothermic Reactions Example 2

here. We need to determine which of the following is an extra thermic reaction for D. We're gonna have steam condensing, so just make sure you see steam condensing there. Now it says, um, if we look at the options we have sealed to burning now, burning usually can notes that we're breaking something down. You know, you you burn a piece of what it breaks it down. You're breaking bonds. So that would be indicative of an Indo thermic reaction not in exile. Thermic reaction. Remember exile? Thermic Is bond forming, not bond breaking next reaction in a cold pack? Well, a cold pack feels cold to the touch, But we said earlier that eggs authentic reactions which release heat feel warm to the touch. So ah ah, hot pack or heating pack would be an extra thermic reaction. Dry ice sublime ing. Remember, if you're sublime ing, you're going from a C. You're going from a solid to a gas. But remember, we're talking about forming bonds. We wanna go do deposition where we're going from a gas toe, a solid three, only one that makes sense. In terms of X, a thermic process is steam condensing. We're going from a gas to a liquid sore, forming bonds. So remember eggs, a thermic reactions or bond forming heat. Releasing reactions mean D is the only option that makes the most sense.