Learn about Senior Chemistry, Energetics 10, in this comprehensive video by bannanaiscool.
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Male Speaker: But you can do labs to calculate the molar heat of solution, that's just like taking an ionic compound like salt and dissolving it in water and finding out what the heat change is, whether it's exothermic or endothermic, heat is absorbed or heat is released. Molar heat of a solution can be called molar heat of ionization because it's an ionic compound, molar heat of dissociation when you combine an acid or a base in a calorimeter you can calculate the molar heat of neutralization when they are put together. So, all of those however are very similar in that, you can use the formula, NH, it was NC delta T to be able to calculate that molar heat -- so, chemical change, well first of all again base change when molecules are separated and you break their intermolecular bonds but if you go to intra here, now all of sudden you might be able to take these elements and make new types of compounds and that's a chemical change. So, chemical changes while we can represent those in different ways too here we have some chemical changes that are written down here as equations and look at this one, here is some glucose that's undergoing fermentation and forming carbon-dioxide gas and ethanol, which is drinking alcohol. Now this reaction right here says that 68 kilojoules are also produced and that means this that this reaction is exothermic. Exothermic because this is the amount of energy net that comes off of this reaction and what do I mean by net, okay, now stay with me here. In order to break the bonds here, energy has to be added to this chemical and then every time bonds form energy is released by the way that's immutable again, you cant just, you have to understand this is very vital that when bonds formed energy is always released. When bonds are broken, energy is always required in order to break. So, energy has to go in, energy comes off, the change is 68 kilojoules, 68 kilojoules more released than added and so we can represent this number here in the equal not in the equation but out of the equation but actually you are writing something called delta H notation so this can be actually as the delta H for this reaction equal 68 kilojoules and you put a negative in front of the 68 because that says that there is a net amount of heat released in this reaction, okay, so any time you see the heat term on the right hand side of an equation when you take it out into delta H notation which stands for the change in entropy the change in heat content when its negative you have got yourself an exothermic reaction when the heat terms on the right side now. Here is another reaction, here is water gas and we are taking it and breaking it down into its elements hydrogen and oxygen, now you are saying you got a one, one and one and half there, why don't you just balance it, two, two, one, yeah I could do that but that the heat here will change, okay, so just always be careful of that if somebody says well less double the balance of here, anybody double the heat, lets half the balancing so you got half the heat. So, in this case right here this actually represents the molar decomposition, one mole of this decomposing into its elements as opposed to if it was reversed the molar heat of formation of that compound. Now, if we were to write this which is an endothermic reaction, as a delta H, the delta H for this reaction would be positive 241.8 kilojoules because that was endothermic, that heat term used to be on this side, so its going to be a positive delta H that means endothermic again. Now, if you reverse the equation when you do you reverse it, it just turns of it from endothermic to exothermic, right and so again that gives you in that case in this one here, it will decomposition, the reverse of that is a -- and now you know we have to got do these, we are a kind of represent them on graphs.