 Let's do this thermo question then. Okay, what does it say? The following information is given for ethanol C2H50H at 1 atm. The boiling point is 78 degrees Celsius. Heat of vaporization is 200 calories per gram. Melting point negative 114 degrees Celsius. Heat of fusion. 26.0 calories per gram. How many calories of energy are needed to vaporize 47.2 grams sample of liquid ethanol at its normal boiling point of 78 degrees Celsius? Okay, so it gives us a number of different values for these different points and you just got to figure out which ones you need to use. So the first thing that definitely we're going to use is the mass of ethanol. That's going to be what's given 47.2 grams. And then it says it vaporizes. So remember vaporizing is going from a liquid to a gas. That's vaporizing. So what we find is we have this amount of energy that's associated with this. We call this the heat of vaporization. So that's delta H that. Or what they've written here is heat of vaporization. So we need to know that number. 200 cal per gram. Then it says how many calories of energy are needed. Well what you want to know is that energy is the units of energy are calories. And it tells you that in the problem if you didn't already know that. And all you want to do now is effectively figure out how do I get just calories from these numbers. So remember chemistry is the science of canceling out units. So here you've got grams and here you've got calories per gram. So what you can do is you can go backwards and think of a formula for this. Well what is energy? What should that be? Well you know you've got 47.2 grams here. And you want this energy to be in calories. So if you take this and multiply it by this number, grams are going to cancel. And you're going to get calories left. So when you do that, that cancels. So you could actually go backwards and think of the formula. Energy equals mass times delta H of vaporization. In this case. And when you do that, you get 9, 4, 4, 0 cals. And it wants it in cals but unfortunately it's only given us 1 sig fig for that 200 there. So we're going to have to cut this down to 1 sig fig. So it's going to be 9 times 10 to the 1, 2, 3 calorie. Because this 200 only has 1 sig fig. Are there any more questions before I shut it down?