Exothermic and endothermic: Common processes and solved examples

- [Instructor] In this video, first we are going to look at some common processes and we will try to identify them as exothermic reactions or endothermic reactions. And after that we will solve some more problems related to exo and endothermic reactions. But before that, let me quickly tell you what they mean. So exothermic reactions are those in which a lot of heat is given out, whereas endothermic reactions are those in which lot of heat is taken in. Now with this, let's begin. So here I have respiration, photosynthesis, and decomposition of vegetable matter. Now I would like you to pause the video and think about which of these processes give out more energy, and which of these processes require more energy. Give it a try. Now if you have tried it, let's see. So see, respiration is a common process that even happens within us. Our cells, they take in oxygen and use that to break down glucose, and in this process we get the energy that we need to survive, run, and play, and things like that. So this process, this gives out more energy. That's why respiration is exothermic in nature. Let's look at its chemical reaction. So here oxygen is getting utilized to break down glucose, and gives out carbon dioxide, water, and energy is released, which helps us do our activities. Now let's talk about photosynthesis. Now you'd remember that plants use this process to make food for almost entire living world. They use carbon dioxide, water, and the energy from sunlight to make glucose. And since energy's being used over here, that's why this is called an endothermic process. This the chemical reaction. See here, sunlight energy's being used to make glucose from carbon dioxide and water. And that's why this is endothermic in nature. And you can also notice that this reaction is totally the opposite of respiration. See, in respiration, carbon dioxide and water and energy were being produced, whereas in photosynthesis, carbon dioxide, water and energy are being utilized to make glucose. So that's how I like to remember, that photosynthesis is totally opposite of respiration. Respiration is exo, it gives out energy, whereas photosynthesis is endo, it requires energy. Now let's talk about decomposition of vegetable matter. This is a tricky one. See, this has the word decomposition in it. Now in the video of exo and endothermic reactions, we have seen that, in general, decomposition reactions. Meaning the reactions in which a big molecule is breaking down into smaller molecules, decomposing into smaller molecules. This generally requires a lot of energy. That means, in general, not always, but in general, decomposition reactions are endothermic in nature, but not this one. This one releases more heat. This is exothermic in nature. See, basically what happens, when we throw off unused vegetables or fruits, bacteria and fungi, they all act on it and they decompose it, they break it down. Now in this process, a lot of energy's being released, and that's why this is an exothermic process. Now how I like to remember this is, basically when you throw away vegetable matter, it decomposes and it becomes manure or fertilizer. And fertilizers, basically, give energy to plants, right. So in this process, energy's being released, and that's how I remember that decomposition of vegetable matter is an exothermic process. Now I have these reactions, and let's try to identify them as exo and endothermic reactions. Now first of all, I would want you to pause the video and try this by yourself. Now if you have tried it, let's see. So here in the first reaction, I can see that heat, or delta, is being mentioned on top of the arrow. Now this symbolizes that this reaction requires heat to begin or proceed, and we know that reactions that require heat, they are called endothermic. So this is going to be an example of endothermic reaction. Now let's look at this one. See in this reaction I can see that plus heat, or plus delta, is written in the product side. Well, this means that heat is being evolved along with the product. And in reactions in which heat is evolved or generated, is given out, we called them as exothermic reactions. So this is going to be an exothermic reaction. Now let's look at this one. Here I can see that calcium oxide, plus water, is giving me calcium hydroxide. So I can see that two reactants are combining to give me one single product. That means that this is an example of combination reactions, and we have seen earlier that, in general, combination reactions give out more heat, meaning I can guess that over here also, more heat will be given out, and such reactions are called exothermic reaction. And yes, my guess would be right over here. See, we have seen this in an experiment when you add water to a white powder of calcium oxide. Then if you touch the container in which this reaction is happening, it will become more warm. That means a lot of energy, lot of heat, is being given out, and that's why this is exothermic. Now let's look at this one. Here I see that lead nitrate is breaking down into lead oxide, nitrogen dioxide, and oxygen. So over here I can see that one single reactant, one big molecule, is breaking down, or decomposing, into multiple products. And these reactions are called decomposition reactions. And we have seen earlier that, in general, decomposition reactions require a lot of heat. So my guess over here will be, that still this is a decomposition reaction, this will also require a lot of heat and such reactions are called endothermic reactions. So I will guess that this is an endothermic reaction. Let me write it with the same color, endothermic reaction. And yes, my guess will be right, because we will see this in a reaction that when we heat lead nitrate, you get some brown colored gas, which is nitrogen dioxide. And in this reaction, we do not get any heat or light, whereas we had to heat the lead nitrate. We had to provide in some heat, and that's why this is an endothermic reaction. Okay, with this we have saw many examples related to endo and exothermic reactions.