hello this is mr. Millington today I just want to explain the concept of latent heat of fusion and latent heat of vaporization all right then I want to apply those concepts to several different examples later on in this video all right so let's take a look at an example let's suppose I have an ice cube and I throw this ice cube out in the middle of a street on a hot summer day well what's going to happen to this ice cube it's going to melt all right furthermore let's suppose I fill an ice tray up with water and I throw it in the freezer what's going to end up happening to that ice over time well it's going to freeze okay latent heat of fusion people is the amount of energy it takes to turn a solid into a liquid or a liquid back into a solid all right so when we're discussing heat of fusion we're looking at the amounts of energy that are absorbed or released by substances as they change change States and matter from solid to liquid or liquid to solid all right let's take a look at heat of vaporization all right let's suppose I have a pot of water and I throw it on the stove and I turn it on full blast well what's going to happen to this water over time is that it's going to absorb thermal energy from the stove from the flame of the stove and what's going to happen to it well over time it's going to boil alright at 100 degrees Celsius this water is going to start boiling okay furthermore let's suppose you get out you get out of a shower on a on a cold winter morning right and you go to comb your hair and there's all this water on your mirror well what has happened there is that those water molecules that were in the gaseous stage hit that cold mirror and those water molecules condensed and turn back into a liquid alright so in these examples over here we've got a liquid turning into a gas and a gas turning into a liquid two different changes in state of matter and when we talk about heat of vaporization we are referring to the amount of energy that is associated with a liquid turning into a gas or a gas turning into a liquid so what we're going to do today is we're going to talk about he diffusion and latent heat of vaporization and take a look at the energies that must be released or absorbed when these two processes or rather when these four processes take place okay so let's take a look at the next slide okay in this slide here just want to talk a little bit about the heat of vaporization and heat of fusion of water specifically now each substance has its own heat of vaporization and heat of fusion however right now we're just going to talk specifically about water all right let's take a look we have some ice over here and this ice is going to melt and turn into water and if I continue to heat this water up or add some sort of thermal energy to this water it's going to turn into water vapor over time all right conversely if I cool this water vapor down it's going to condense and turn back into water and if this water loses more energy or thermal energy or releases thermal energy it's going to turn back into ice so what we're going to do in this little slide is talk about the heat of fusion of water and the heat of vaporization of water as they change States and matter okay so let's start over here with the ice okay let's suppose I have some ice and this ice here is at at its melting point or freezing point of zero degrees Celsius okay and what we're going to do with this ice is we're going to throw it under some sort of heat source okay whether it's a Bunsen burner or the Sun or or a stove alright and what's going to happen to this ice if we do that is it's going to melt it's going to melt and turn into water okay but let's suppose that there is no temperature change let's suppose all this takes place at zero degrees Celsius which is the boiling point or melting point of water all right in that case here we will have to take a look at the heat of fusion for water all right in other words if I've got one gram of this ice here and I want to melt it and turn into water how much thermal energy must this ice absorb in order to turn it into water well the answer to that question is right here it will take 334 joules the thermal energy to turn one gram of ice into water now you'll notice that the sign of this heat of vaporization here is positive and it's positive because melting ice is an endothermic process and anytime we have an endothermic process the sign will be positive okay let's go the other way what if I've got some water and I want to freeze it okay if you have some water and you want to freeze it then those water molecules must lose a certain amount of thermal energy in order to change a state matter and convert it into ice well how much thermal energy do you think needs to be lost well that's right here if you take a look going the other way this water will need to release 334 joules of thermal energy to convert it back into ice and as you see right here the sign of this is negative okay water turning into ice is an exothermic process and therefore the sign for the heat of fusion should be negative let's look over here on the other side okay if we take a look at the other side here we've got water turning into water vapor now let's suppose that this water here is turning into water vapor right at around 100 degrees Celsius which is the boiling point or condensation point of water all right we want to know how much thermal energy must this water absorb in order to turn it into water vapor well the answer to that question people is right here if you take a look here if you've got one gram of water at a hundred degrees Celsius and you want to turn this into water vapor at 100 degree Celsius then this water right here will need to absorb two thousand two hundred and sixty joules of energy you'll notice once again that the sign in front of here is positive okay that is because turning water into water vapor is an endothermic process this water here must absorb thermal energy from its surroundings to change its state of matter into water vapor all right let's look the other way what if we have some water vapor here that's water in the gaseous state and we want to condense this and turn it back into water well how much thermal energy must this water lose in order to turn it I'm sorry I must as water vapor lose in order to turn it back into water that answer is right here the heat of vaporization for water right exceptional notice right here that the sign is negative okay in order for these water vapor molecules to slow down and turn back into water they must release a certain amount of energy okay and whenever we release energy the sign will always be negative okay now different substances have different heats of fusions and different heats of vaporizations so this is here these numbers right here that 334 and the 2260 joules per gram are only specific to water so let's take a look at some heats of fusions and heats of vaporizations for other substances okay if we take a look at this table all this table is showing us is the heat of vaporization and the heat of fusion for various substances we have water we have lead we have aluminum and we have gold and like we just said in the the slide before this that the heat of fusion for water is 334 joules per gram so if I have one gram of water and I want to melt one gram of water it will take 334 joules of thermal energy to do so or five one gram of water here and I want to turn it into water vapor that water will need to absorb two thousand two hundred and sixty joules of energy in order to do so alright so in this table here I just wanted to show you that different substances have different heats of fusions and different heats of vaporizations if you take a look lead the heat of fusion is twenty four point five joules per gram that's a heat of vaporization is 870 joules per gram etc etc so if we take a look at this question down at the bottom it says how many times more energy does it take to boil water compared to melting ice assuming they have the same masses and are under the same amounts of pressure well if you take a look here the heat of fusion for water that is the amount of energy it takes to melt ice and turn it into water is 334 joules the heat of vaporization that is amount of energy it takes to turn water into water vapor is 2260 joules so as you see right here if you compare these two you can see that it takes about seven times more energy to turn water into water vapor than it does to turn ice into water okay so the answer to this question right here will be about seven times more energy to turn water into water vapor compared to ice into water okay now that we have the concept of heat of vaporization and heat of fusion down we're going to work some with some examples relating to water and the heat of vaporization and heat of fusion of water so let's look at this example here in this example we need to calculate the amount of energy associated with changing 100 grams of water to water vapor at a hundred degrees Celsius now this is important right here a hundred degrees Celsius if we take a look at this there is no change in temperature all right there is no change in temperature all the energy in this problem is going to changing the state of matter if we have a change in temperature then that's a totally different problem that I will show you in a subsequent video so let's take a look at this though okay we want to calculate the amount of energy associated with changing 100 grams of water to water vapor alright so if we want to turn water into water vapor this is going to be a heat of vaporization problem and we must use one of these two heats of vaporization so let's take a look here we've got 100 grams of water and we want to know we want to know how much thermal energy this 100 grams of water will need to absorb to turn it into water vapor all right so we want to turn this water into water vapor so what are we going to use we are going to use this right here right we are going to use the heat of vaporization right here right turning the water into water vapor is an endothermic process so we'll use this top one right all right so let's go ahead and solve this problem here all right we know that it will take two thousand two hundred and sixty joules of energy that this water will need to absorb per gram okay of water so this will now cancel out with this unit here and now you just get your calculator out and your final answer should be two hundred and twenty six thousand joules of energy and our sign on this will be positive because that water is going to need to absorb this much energy and anytime something absorbs this much energy our sign will be positive let's take a look at the next example alright in this example here it says to calculate the amount of energy associated with changing 250 grams of water to ice at zero degrees Celsius so once again there is no temperature change in this problem the temperature is staying the same what's happening is that this water is going to release a certain amount of energy and once it does so then if it continues to release more energy all that energy I'm sorry the temperature will stop start to decrease alright so here we go we've got 250 grams of water alright and if we take a look at the question here this water is going to turn into ice alright so we've got water turning into ice this looks like a heat of fusion problem right here and because the water is releasing energy in order to turn into ice you'll take a look at the sign in front of the number here and it's negative okay so we know that one gram of water is associated with 334 joules of energy and if we take a look the water is turning into ice so our sign should be negative so we get our calculator out and we simply take 250 times negative 334 and we'll end up with our answer of negative eighty-three thousand five hundred joules alright so the question here how much energy is associated with the with changing 250 grams of water to ice at zero degrees Celsius well it looks like this water is going to need to release eighty three thousand five hundred joules of thermal energy in order to do so fix that here alright let's take a look at another example alright in this problem here we are asked to calculate the amount of energy associated with changing ten grams of ice to water so in this problem here we've got ten grams of ice right and this ice is going to melt and turn into water so this looks like a heat of fusion problem right a heat of fusion problem okay so let's go ahead and jump right in here so we've got let's see 10 grams of ice which essentially is water and because this is a heat of fusion problem we know that the heat of fusion of water is 334 joules for every gram right that means in order for ice to turn into water it must absorb 334 joules for every gram of water right and because we're going from ice to water this ice is going to have to absorb thermal energy and so our sign here should be positive this unit right here will cancel out with this unit right here put this in your calculator and you should end up with this answer right here with a positive sign so how much thermal energy must 10 grams of ice absorb in order to change it into water all of this of course is happening at zero degrees Celsius with no temperature change 3340 joules must be absorbed let's take a look at another example alright in this example we have to calculate the amount of energy associated with changing 200 grams of water vapour to water ok so in this problem here we've got 200 grams of water vapor and this water vapor is going to release a certain amount of energy and it's going to convert into water and what we have to do is we have to figure out how much thermal energy this water vapor needs to release in order to turn it back into water ok so in this problem here we've got 200 grams of water vapor that's h2o that's in the gaseous state and we want to know how much thermal energy people this water vapor will need to release in order to change its state back into liquid water well we know that the heat of fusion I'm sorry the heat of vaporization for water is 2260 joules for every gram of water however let's take a look at what's happening this water vapor is releasing energy in order to convert it back into water so our sign here is going to be negative so now we have this set up correctly grams of h2o will cancel out grams of each tool will cancel out I get my calculator out here and I take 200 times a negative 2260 and you will end up with a negative 450 mm okay so this 200 grams of water vapor will need to release four hundred and fifty-two thousand joules of thermal energy in order to change it all back into water so I hope you guys understand the concept of heat of vaporization and heat of fusion and I hope you guys are able to use the examples that I provided in this video to solve some of your own chemistry problems dealing with thermo chemistry I hope this was helpful