moving on we're talking about matter and energy so don't forget the key properties matter has mass takes up space common forms solid liquid and gas energy the capacity to do work has no mass takes up no space also in several different forms things like heat light sound motion electricity scientific observations and experiments over the course of centuries have led to a very important law regarding matter called the law of conservation of matter it goes like this the law of conservation of matter in a physical or chemical reaction matter is neither created nor destroyed matter neither created nor destroyed the amount the mass of matter stuff that you have at the end of a process any kind of process the amount that you have at the end is identical to the amount that you had at the beginning neither more nor less identical the idea here is that the amount of material you have at the end of a process is identical to the amount that you had at the beginning nothing goes away or disappears if something seems to have disappeared it's probably because it changed form so that you don't see it anymore for example a solid turns into a gas the gas escapes during a physical or a chemical reaction when i first introduced this law to you i wrote it up on the white board at the beginning of our discussion of what is science to explain what a scientific law is i left out the physical let's explore that now a chemical reaction you will understand you put two substances together they react and create something new in a physical reaction there's no chemical change there's no new substance created you're dealing with the original substance or substances so what changes are we talking about changes of form solid to liquid to gas things like that here's an experiment you could do at home get up in the morning go to your freezer get out some ice cubes stick them in a pan weigh it let's say you have a pound of ice cubes leave the pan out on the kitchen counter off you go to work or school come back in the evening take a look do you still have ice cubes no you don't you have a pool of water in the pan and it looks smaller it's kind of run together the ice cubes were a pile now it's a consolidated pool of water where the pan again is the pan going to weigh more or less now that it has water in it then it did in the morning when it had ice cubes what do you think well it's going to weigh exactly the same all the water molecules all the h2o molecules are still right there in the pan they're rearranged they look different they've changed from solid to liquid but they're all still there and when you weigh them all they weigh the same okay now let's take that panel of water put it on the stove turn the stove to high what happens water gets hotter and hotter it starts to boil now let's leave it there on the stove on high as it boils and bubbles away gradually the level of the water goes down down down down down why it's turning into steam turning from liquid to gas and going into the air if we could collect the steam and weigh that what would that weigh exactly the same as the water exactly the same as the ice cubes no more and no less which actually makes her other interesting point many of you i'm sure have cooked something up slowly long time and the level's gradually gone down from time to time you have to add a little bit more water to the pot so it doesn't cook down too much if you have boiled off a pint of water into your kitchen that pint of water is there in your kitchen in the air if the temperature is cool that pint of evaporated water is condensing into drops of water on the ceiling drips running down the wall any drapes are feeling awful heavy because they've got water condensed into them pieces of paper aren't crisp anymore they're kind of limp and soggy unless of course you have open windows or a fan and you're moving the air through your kitchen and out into the great outdoors and getting rid of the water that way okay law of conservation of matter how about a chemical reaction well if it was winter this would work how about burning a log of wood in your fireplace okay you start out with the wood and you burn it and what are you left with ash does the ash you're left with weigh the same as the wood that you started with no absolutely not the wood was heavy and the ashes feather light well that tells you that that wasn't the whole story there's something that you've missed what have you missed you've missed the gases from that burning that went up the chimney what are the principal gases you're going to get from burning wood well wood like all organic materials is made of carbon atoms and hydrogen atoms and a few others the burning process is when you react your substance with oxygen from the air and so the hydrogen atoms reacted with oxygen form hydrogen oxide or water and the carbon atoms form carbon dioxide and both of those are gases and they go up the chimney now the sheer fact that you burned a lot of wood and you wound up with a tiny amount of ash means that nearly all most of what you burned turned into h2o and co2 is there any environmental downside to putting a quantity of h2o into the air no not at all is there an environmental downside to putting a quantity of co2 into the air absolutely co2 carbon dioxide the principal cause of global warming climate change if you've burned 20 pounds of wood you've put something of the order of 20 pounds of carbon dioxide into the atmosphere and that's a lot now i'm not trying to guilt you out of having the fire in your fireplace yes there are no burn days and all that but the point to realize is that everything we do puts carbon dioxide into the atmosphere a lot of it more than i think most people realize now this chemical reaction still isn't quite complete i said what do we need in order to burn the wood burning is when we react our fuel with what the oxygen from the air so there's your chemical equation if you like wood plus oxygen turning into ash plus water plus carbon dioxide and the weight of everything on the left here equals the weight of everything over on the right law of conservation of matter now your fireplace is no place to demonstrate the law of conservation of matter you don't have enough control you know how much wood you brought in and burned but you have no idea how much oxygen was pulled from the air in your room to burn it although have you ever noticed if you have a fire in a room there are powerful cold drafts sucking in under doors through cracks in windows and stuff like that that's the fire pulling in the oxygen that it needs you know exactly how much ash is left after you finished burning how much you shoveled out of the grate when you were done but you have really no idea what went up the chimney you just realized that it was a lot but scientists can do this experiment in a more controlled environment and very easily very clearly demonstrate the law of conservation of matter you need a sealed container i recommend glass for one thing you can see through it and see what's going on inside for another you can fairly easily melt glass and cause it to seal together so you get yourself a glass tube one ends closed you put in a piece of wood you pump in oxygen and then you seal up the other end okay so wood oxygen in a glass sealed container weigh it you've got the total weight of the glass which isn't going to change and the weight of the starting substances now apply flame that's another neat thing about a glass container and you can apply heat with a flame on the outside the heat will go through the glass pretty well and heat up what's inside apply heat until the wood bursts into flames you can see it catch fire pretty soon your vision gets kind of obscured because the h2o that's being produced mists up the inside of the glass and spoils your view but you know how long it goes on burning and eventually the fire goes out and if you give it a tap you'll find that instead of a lump of wood you've got a loose pile of ash in its place let it cool down the glass tube is still sealed nothing got in nothing got out but you don't have any wood anymore you can see ash take that last tube and weigh it again guess what it weighs exactly the same as it did when you started although now you can see drops of water a pile of ash you can't see co2 carbon dioxide is an invisible gas but once you've got your weight and you know what you're dealing with you can break open the tube get the carbon dioxide out and chemically measure but it is carbon dioxide and how much you have so yes it is perfectly possible to demonstrate the law of conservation of matter using this chemical reaction the weight of the starting components is exactly equal more or no less to the weight of the ending components whatever they may be