How do candles burn? (and how do you light them with smoke?)
Hey. I'm Melissa.
Jam:And I'm Jam.
Melissa:And I'm a chemist.
Jam:And I'm not.
Melissa:And welcome to chemistry for your life.
Jam:The podcast that helps you understand the chemistry of your everyday life.
Melissa:Of your everyday candles. Oh. Well, that's what we're gonna be talking about today, the long awaited since Our experiment aired on Monday.
Jam:Nice. Very cool.
Melissa:So we're gonna be talking about, 1, how candles work.
Jam:Okay.
Melissa:2, How that magical smoke trick works?
Jam:Right. Right.
Melissa:So have you thought at all about that magical smoke trick since?
Jam:Just We did it. A little bit, but I don't know if I have any strong Theories, but I actually, maybe. Should I try to throw 1 out there or just let you tell me?
Melissa:Yeah. Try to throw 1 out there.
Jam:Okay. So I know we've talked about fire before, and it's that's still a mystery to me in a lot of ways even though We talked about it. Yeah. I think our episode was, like, what is fire? And I'm still kind of not always sure.
Jam:But One thought I have was just the fact that the we talked a lot about energy being a part of that. And, also, smoke maybe still has some energy to it or something like that because it's not like it would all just be gone or even thinking think about heat. You know? Yeah. It's like it'd all be gone immediately when the fire's blown out.
Jam:So my thought was maybe there's something to the fact that the smoke Still has some of the makings of fire in it regardless of how unscientifically someone like me might try to put that that might allow it to Catch fire more easily than than, obviously, our our air doesn't just catch on fire In
Melissa:The last thing you said, I think, is the key. There's something still in the smoke that has the makings of fire in it. Nice. Okay. So let's talk about that.
Melissa:And here's how it started also. I guess before we talk about that, a long time ago, Jam Just texted me out of nowhere, no context, what is wax?
Jam:Oh, yeah. Yeah. I did do that, didn't I?
Melissa:And so I was gonna do an episode on that, but what wax is is pretty boring.
Jam:Man.
Melissa:So Wax is a long chain of carbon and hydrogen.
Jam:Mhmm.
Melissa:Usually has a functional group on one side. And because it's long chains of carbon hydrogen, and we talked about this before, the shape of a Carbon bonded to 4 things is what's called a tetrahedral.
Jam:Mhmm.
Melissa:It's kind of a weird shape. You can Google it, look it up, or maybe I can show you on a modeling kit.
Jam:K. And when
Melissa:you have long chains of carbon bonded together in a tetrahedral form, they they kinda make a A chevron. The carbons bonded to each other make a chevron pattern. That up, down, up, down, up, down.
Jam:Got it.
Melissa:And if you have a lot of long chains of that, they can stack into each other really nicely.
Jam:Oh, yeah. We've talked about something else that does that.
Melissa:I can't
Jam:remember what
Melissa:now. But Margarine.
Jam:Oh, yeah. That's right.
Melissa:That's why we hydrogenate oils to make it carbon bonded to 4 things, give it that chevron pattern.
Jam:Right.
Melissa:So if you're trying to imagine At a molecular level, what wax is? It might have a functional group on one side. We've talked a lot about functional groups. It's just arrangement of atoms.
Jam:Mhmm.
Melissa:But the main part that makes it up is a long chain of carbons and hydrogens. So visualize in your mind a carbon bonded to a carbon, bonded to a carbon, and, like, 1 carbon is down, the next carbon is up. 1 carbon is down, the next carbon is up to make a chevron pattern of carbons bonded to each other.
Jam:Got it.
Melissa:And I can also post a video of that on Instagram. So because they fit nicely into each other, they stack well, they're gonna have solid intermolecular forces
Jam:Mhmm.
Melissa:So they'll be able to be solids at room temperature.
Jam:Got it. Got it.
Melissa:That's basically what all waxes are.
Jam:Okay.
Melissa:And there's just variations of functional groups on them, variations of maybe different molecules involved to make them have Sort of different properties, soy wax as opposed to beeswax, as opposed to paraffin wax, but they all are Basically, the same thing.
Jam:Got it. Got it. I think one of the reasons I remember sending that question to you was just I I remember thinking It's pretty unique how it can become liquid and then go back to being a solid and seem to do that so many times. You know?
Melissa:But butter is kinda that same way.
Jam:That's true. I guess I never really reuse butter, so that's why. Like, with a candle Yeah. It's done it so many times by the time the candle's spent that it seems More unique, but, hopefully, you're not doing that with your butter. And for no reason, just heating it up and melting it and then Letting it solidify again and over and over and over.
Melissa:And it does kind of change because it has so many different things in there that the consistency of it change once it melts and solids back. Right. Melt and solidifies back again.
Jam:Right. Right.
Melissa:Okay. So now that we know what waxes are, we can more easily talk about How candles work.
Jam:Okay. Sweet.
Melissa:So one thing about candles that blows my mind is how does that little wick burn forever?
Jam:Yeah.
Melissa:If you just had a string that what you lit on fire, it would burn and be gone. Yeah. And something has to be happening to the wax because candles get lower.
Jam:Mhmm. Yes. That is one of the things I remember asking, like, I think my mom one time as a kid when I lived at home still, maybe, like, middle school. I was like, where does all that wax go?
Melissa:Well, I'm gonna tell you. The answer is so sciency and so cool.
Jam:Okay. Sweet.
Melissa:So for all of you who've ever wondered about this, if you haven't wondered, pause. Take a second to about what could possibly be happening. Yeah. And now I'm gonna tell you. When you light the wick, It gives off enough heat for 2 things to happen.
Jam:Okay.
Melissa:1, the solid wax melts.
Jam:Mhmm.
Melissa:And that Is chemistry right there? You've put enough heat in that the molecules are moving around enough that they've Separated from one another, their intermolecular forces are overcome by the energy put in. We talked about intermolecular forces a lot. Basically, the molecules want to hang out together, but the more energy you put in, the more they're gonna be moving around and they're able to not be as close to each other.
Jam:Right.
Melissa:K. And then that liquid wax through Capillary action, probably. It could also be through I think it's called adsorption where it sticks to the wick Mhmm. Through some intermolecular forces and, you know, the way liquid does. Yeah.
Melissa:The liquid wax is drawn up into the wick. The same way if you put a paper towel into some water and you'll see the water crawl up the paper towel.
Jam:Oh, wow. Yeah.
Melissa:So the liquid wax goes up into the wick, and then the liquid wax is so hot from being right next to that fire that it reaches its boiling point
Jam:Uh-huh.
Melissa:The molecules are moving even more so much that they become gas.
Jam:Wow. Okay.
Melissa:So that's the first thing that happens. The solid wax goes from a solid to a liquid. The liquid is drawn up closer to the point of the Fire.
Jam:Mhmm.
Melissa:And then it turns to a gas.
Jam:Got it. And that at the same time would be preventing the wick from just completely burning up because of there being something else to burn or something?
Melissa:I don't know. The wick is burnt, but I think that wax in there is, yes, Something else to burn. So that's the second thing that happens.
Jam:Okay.
Melissa:The second thing that happens is a combustion reaction. And we talked about that in the episode about what is fire. Mhmm. But, basically, the carbons and the hydrogens in the wax vapor, the gas, It has to be the gaseous form of wax.
Jam:Okay.
Melissa:That reacts with the oxygen in the air. So you have carbons and hydrogens from the wax gas
Jam:Okay.
Melissa:With o 2 in the air.
Jam:Mhmm.
Melissa:And then Those 2 things don't just react. They need energy to form the reaction.
Jam:Okay.
Melissa:So you gotta put a little energy in.
Jam:Right.
Melissa:The heat from lighting the candle is enough energy for the wax vapor to react with the oxygen in the air and have a combustion reaction.
Jam:Okay.
Melissa:And the combustion reaction creates c o two water. The molecules rearrange, you had the carbons, the hydrogens, and and they just rearranged to make carbon bonded with oxygen, hydrogen bonded with oxygen, h two o, c o two.
Jam:Got it. Got it.
Melissa:But the other byproduct of that reaction is energy in the form of heat and light.
Jam:Right. Right.
Melissa:So you put a little bit of heat in to start the reaction.
Jam:Uh-huh.
Melissa:And then once the reaction is going, it gives off so much heat and light that it basically just keeps feeding itself.
Jam:Right. There's a huge source of new things to fuel that Yes. Right below.
Melissa:Yes.
Jam:It's the it makes up the entire candle.
Melissa:Yes. So it's just this Snowball of reaction where, say, you have a little bit of wax that melts, goes up into the wick, Does it becomes gas, does a combustion reaction. That combustion reaction gives us energy that fuels another amount of Wax melting, going up into the wick, turning into vapor. You have enough energy for it to do a combustion reaction. It gives off even more energy.
Melissa:Yeah. And that fuels More wax melting, and that so it's just a repeated reaction that happens over and over and
Jam:over. Yeah. Interesting.
Melissa:So literally, the thing burning in a candle is wax vapor. It's not the liquid wax.
Jam:Yeah. It's
Melissa:not the rope. Mhmm. It is the gas form of the wax reaction reacting with oxygen Yeah. To give off heat and light.
Jam:Man, that's crazy.
Melissa:And because of that, because there's that wax vapor is right there at the candle wick Uh-huh. That's gonna be the hottest point of the flame.
Jam:Right. Right.
Melissa:Because there's so much of the fuel right there in the middle.
Jam:Yeah. Yeah. Yeah.
Melissa:And because it's not the liquid wax that's reacting, it's not as if that whole candle's gonna catch on fire
Jam:Yeah.
Melissa:Unless there's a bunch of gas floating around right over it.
Jam:Right. Right.
Melissa:So when you blow out a candle, That little trail that comes up of smoke is actually
Jam:Wax vapor?
Melissa:Wax vapor. The combustion reaction travels down the wax vapor back to the wick where there's a higher concentration of wax vapor.
Jam:Nice. Nice. So it's like this little leftover aspect of the reaction still happening for a little while
Melissa:Yep.
Jam:Even though we already have extinguished the main Heat source and stuff like that?
Melissa:Yeah.
Jam:If we do it at the right time, we could take advantage of that and
Melissa:Yep.
Jam:Get the reaction all going again. The circle of life going again.
Melissa:And you can visually see just wax vapor and gas don't react with each other. Wax vapor and the oxygen in the air don't make a reaction.
Jam:Right.
Melissa:You have to light that wax vapor. You have to give that energy for the combustion reaction to start over again.
Jam:Right. Right. Right. Dang, dude. That's crazy.
Melissa:It's so sciency.
Jam:Yeah. And more complicated than I thought. I just thought I did think wax would be more complicated, but the whole candle burning stuff, I think I didn't really think was that complicated. I don't know. Yeah.
Jam:Like, I remember whenever I asked my mom that question forever ago, she just said, like, oh, it burns it up. Like, it would it made it seem like, oh, okay. I guess I should've thought that. And just I didn't I didn't really expect there to be this many steps to it and how important it would be to the whole process.
Melissa:I had never thought about what makes a candle burn
Jam:Yeah.
Melissa:Until I was trying to put together an episode on wax.
Jam:Yeah.
Melissa:And then I was just Amazed. I'm amazed. And it's so science y. There's so many different science concepts.
Jam:Mhmm.
Melissa:There's the different states of matter, solid, liquid, gas. All of them are present, which is kinda cool.
Jam:Yeah.
Melissa:Yeah. There's a combustion reaction. There's products of the reaction or heat and light, and then it's just sustaining itself. Yeah. Wow.
Melissa:It's amazing.
Jam:I also remember thinking just the functional part of my brain. I often thought, like, okay. 1st, obviously, candles, We love them now because they smell good. Yeah. The vibes of their light are nice too, but the smell, I think, is the main reason we have them.
Jam:Of course, back a long time ago, it was because of the light that people had them. Yeah. So I think I thought the wax was just there to slow down Everything.
Melissa:Me too.
Jam:So that it would not burn up so fast. It's like, put something in the way of this wick being burnt up So that this little flame will stay around for a while so that I can write my memoirs or poetry or whatever people did back in the day. Institutions, etcetera.
Melissa:More than that.
Jam:Yeah. Wow. Very interesting.
Melissa:Very interesting. I'm very amazed. That is cool. I don't know how people figured out to do this, and I'm really amazed at the science behind it. Yeah.
Melissa:Yeah. You wanna take a stab at telling that back to me?
Jam:Yes. I would love to. Okay. So here's what's kinda coming to mind for me. And I think it's because I've got batteries on the mind because we talked about them last week?
Melissa:Oh, yeah.
Jam:So the way that I started thinking about this was Similar to that where it's like, we've got with the candle, all these things are primed and ready.
Melissa:Mhmm.
Jam:All they need is the thing to start it. It's almost like it's we have a perfect circle of of Kind of a chain reaction kind of thing that'll keep keeping itself going
Melissa:Right.
Jam:Except we're missing one link of that chain. Or in the case of, like, a battery, it's like it's it needs to be connected to itself in order for that to happen, and it's, like, just missing Everything else. You know? Yeah. In this case, we're missing, just 1 little piece Yep.
Jam:But the most important piece. So when we light the candle, The wick starts to burn Mhmm. Which causes the Wax to first melt. The wax is made of carbon and hydrogen.
Melissa:Yep.
Jam:Right? In that, like,
Melissa:Maybe a few other things, but mostly carbon and hydrogen.
Jam:Right. And then and for the reaction, those are
Melissa:The main.
Jam:The main things that we talked about. And first, it turned into a liquid.
Melissa:Mhmm.
Jam:And then it's drawn up into the wick. Yep. In what's the word you used? Capillary action?
Melissa:Capillary action is when there's a small space and water climbs the walls of a Oh, yeah. Of a of a small tube or I think, technically, I should've looked this up, but I didn't. So don't hold me to it.
Jam:Okay.
Melissa:There's a word like adsorption or adhesion, something like that, that means a molecule clinging to the walls of something else. Uh-huh. And that's kind of what causes the
Jam:Got it.
Melissa:I think.
Jam:So it's drawn up
Melissa:Drawn up.
Jam:To the heat, the hottest part.
Melissa:Yes.
Jam:And when it gets there, It turns from a liquid into a gas because of the heat. It boils.
Melissa:Molecules are moving around, wiggling around so much get further and further apart.
Jam:Right. Right. So we've got already that point, we've got had all 3 states of matter. Yep. It went from solid to liquid to gas.
Jam:Yep. And then as it turns into that wax vapor
Melissa:Mhmm.
Jam:With the heat right there
Melissa:Mhmm.
Jam:It is able to React with the oxygen
Melissa:Yep. In
Jam:the air and combust Mhmm. And Turn into something totally different where the carbon and hydrogen, react with the oxygen to then instead Have CO 2 and h two o as the would you say byproducts of that? What do you call that?
Melissa:Yeah. Byproducts or the just the products of the reaction.
Jam:Products.
Melissa:Yeah.
Jam:But they combust, which keeps The reaction going because it is heat and allows that flame to just keep being almost like relit over and over and over. Right?
Melissa:Right. And when we are teaching students this concept, we put heat as a product or a reactant. So
Jam:Oh, yeah. Yeah.
Melissa:You need energy to start the reaction. So In the form of heat is what we do. So there's, like, a little bit of heat on this side Yeah. Plus the carbons and hydrogens and the oxygen, and then we put an arrow Uh-huh. To say, like, that makes water, c o two, Heat and light.
Melissa:And you have the students draw the heat and the light in as part of a byproduct of the reaction.
Jam:Right. And there's also the beginning of the next.
Melissa:Yep. Because you have some heat and light Yeah. To fuel. I guess you don't need light to fuel, but heat to fuel The next.
Jam:Yes. Yeah. So it's the beginning of one thing and the end of another.
Melissa:Yep. And That'd be a fun way to draw this. This is not chemically proper, but if you did eat The wax molecule Yeah. The oxygen, and then an arrow. And then you did heat, c o two, water, plus Wax molecule oxygen and another arrow.
Jam:And if you just did it in a circle Uh-huh. To where heat is the last one, but also the first one? Yes. That'd be kinda cool?
Melissa:That would be pretty cool. That would be really cool. Yeah. So this
Jam:is I was kinda imagining, like, a circle
Melissa:Yeah.
Jam:With the in my head and just like a piece missing, which is the heat. Yeah. So, is that right? Did I miss anything?
Melissa:I think that was perfect.
Jam:Dude, that's interesting.
Melissa:That is so interesting. I was amazed. So Very cool. Also, it occurred to me, and I wish we'd thought about this for Monday's episode when we recorded that. That experiment, you know, is a more advanced experiment.
Melissa:But if you wanna just to kids about it. You can have a candle and put it under a jar Mhmm. To a clear jar or something that will keep the oxygen out, and they can see the flame extinguish.
Jam:Uh-huh. Uh-huh.
Melissa:And that's a great conversation starter with your kids about flame as well. And Where does the flame go? What do you think is happening?
Jam:That kind
Melissa:of thing.
Jam:I remember being shown that as a kid at some point by a teacher or somebody and just being like, woah. A guy didn't really think about The fact that something could be extinguished without touching it or, like, blowing on it Yeah. And just, like, starving it of oxygen was something that was totally new for me. I remember thinking that. It seemed really magical.
Melissa:It is pretty magical. Yeah. I didn't even think about doing that. Maybe we'll do a separate chemistry at home episode on that. Yeah.
Melissa:On down the line.
Jam:Sweet.
Melissa:So that's it. That's how candles work. I'm amazed by that. I think it's so fun and cool. But, also, is there something so fun and cool from your week this week that you wanna tell me about?
Jam:Sure. I'd love to. So This is one that I thought about a few days ago that I is not a huge deal. Okay?
Melissa:Okay.
Jam:But I think that you and many of our listeners will be able to relate to this feeling that I had, that Even though it's a podcast that I've listened to that probably most people haven't, the feeling that I had, I think, is one that you guys will be able to appreciate. Are you ready?
Melissa:I'm ready.
Jam:Are you curious? Are you like, what the heck is he gonna say?
Melissa:I have no idea what you're gonna say.
Jam:So one of my favorite podcasts, Which is not actually a podcast. It's an Internet radio show, which we don't have to get into, called Time Crisis
Melissa:Okay.
Jam:Toasted by Ezra Koenig, the lead Singer and songwriter of Vampire Weekend
Melissa:Okay.
Jam:And his friend, Jake Longstreth, who's a painter.
Melissa:Okay.
Jam:And it's been, like, one of my favorite shows to listen to for the past couple of years.
Melissa:Okay.
Jam:But I got into it When they'd already had tons of episodes done.
Melissa:You know?
Jam:You know that feeling when you're like, okay. I love this. There's so much here.
Melissa:Never run out.
Jam:They'll never run out. I, After crying for maybe, like, two and a half years, finally caught up
Melissa:Oh my gosh. On
Jam:maybe I didn't say the name of it. Time crisis is what You
Melissa:said that, I think.
Jam:Yeah. So I finally caught up on time crisis. And this is actually a couple weeks ago that I did that, but I realized How nice of a feeling it was and how I have to share that.
Melissa:That feeling always makes me sad.
Jam:So I didn't feel sad. I mean, I felt a little, but I did feel like what's nice is that now when a new episode comes out, I'm more excited.
Melissa:That's true. That's true.
Jam:And it's very current, and I'm like, oh, I'm hearing about what they're talking about right now
Melissa:Right now.
Jam:What's happening in their lives or, like, The commentary that they are having about something happening in the world, I'm up to date on it.
Melissa:I think then I just feel a little empty. Like, now what am I gonna listen to?
Jam:Mhmm. Yeah.
Melissa:It took me my go to.
Jam:Yeah. It took me so long to to catch up that it did feel like I was never going to. Yeah. And I did often feel like, man, I missed that. Or, like
Melissa:Well, congratulations. Yes.
Jam:Yeah. And they do a lot of, like, referencing things that happen in real life. So that always made me feel like, Man, I wish I was listening to this while that thing was happening. Yeah. Because I would be kinda laughing with them about whatever.
Jam:So, anyway.
Melissa:Very cool.
Jam:So that's my good thing. So shout out to time crisis on Apple Music. Definitely check it out if you like music And, people talking about music and people talking about corporate food history.
Melissa:Corporate food history. Interesting.
Jam:Yeah. That's one of their main segments is they kinda do dives into, like, corporations and food and the weirdness of our culture here in the United States about the roundabout. So so
Melissa:I can always get behind people talking about how weird the United States Is.
Jam:Oh, yeah. Yeah. What about you, Melissa?
Melissa:That was definitely a good one. I think this is a few fun things all rolled into 1.
Jam:Okay.
Melissa:My sister lives in another state.
Jam:Mhmm.
Melissa:And she happens to be coming into town this weekend.
Jam:Did you mean another state of matter?
Melissa:No. Another state in the United States.
Jam:Got it. Okay. That makes more sense.
Melissa:And she happens to be coming into town this weekend. Uh-huh. And it's her birthday. Nice. And she didn't plan that on purpose.
Melissa:She's in town for an unrelated reason.
Jam:Yeah.
Melissa:But I'm so excited, and I get to actually make my sister a birthday cake, which Making birthday baked goods or special event baked goods for people I love is an act of love for me. I love doing it. It's something I wanna do. I want them to enjoy really carefully made, full of love things on their birthday and or Special event.
Jam:Yeah. Yeah.
Melissa:So it's also my brother's birthday. Weirdly, they're born one day apart. Woah. 3 years apart. If my brother had been born just a few years later, he also they would have shared a birthday.
Jam:Oh, interesting.
Melissa:Isn't that crazy? 3 years apart. But so I get to celebrate both of them. I get to make a, not a cake, a baked good for both of them, and it required me making Caramel sauce for the first time ever.
Jam:Okay.
Melissa:And that went really well and was really fun. Uh-huh. And the thing I made was a turtle pie, so inspired by those Turtles they're called turtles. They're caramel pecans with chocolate on them.
Jam:Yeah. Yeah.
Melissa:And it was really fun, and I really enjoyed it. So I'll send some pictures along of that On Instagram.
Jam:Dude, very cool.
Melissa:I'm so excited about that. I am so excited to celebrate both of my siblings' birthdays together. I'm so excited that I got to bake for I'm so excited that I made caramel for the 1st time. It was just all around a really fun thing.
Jam:Yeah. So sounds like a pretty boring week. Anyway, just kidding. You see it's exciting so many times in a row. It's like it's so so funny because Melissa really does love baking that much.
Jam:And, like It's true. I probably already shared this, but how You called dibs on being able to bake the cake for my son's birthday well before we were even, like, thinking about doing that stuff?
Melissa:Probably late December of last year. Yeah. Because so like, 6 months old.
Jam:Yeah. This is so funny to me because it's, like, not My thing at all, but you can just tell that Melissa gets, like, a ton of joy out of doing it. So
Melissa:I love it. I want people to enjoy it. Like tweaking recipes until they're perfect. It's just really fun.
Jam:Yeah. Very cool.
Melissa:Yeah. Thanks for letting me Bake your son's birthday cake. That was the most fun. And, also, thanks for coming and learning about candles and being as interested in it as I was. And thanks to all of you listeners For coming each week to learn about chemistry, it really is so fun and so special for us every single week.
Melissa:If I could, I would bake all of you a little big good to show how How much I love and appreciate y'all, but it is not feasible. Yeah.
Jam:That's very true, unfortunately. But you can just share the pictures of your baked goods with all of us. That's As close as we can get.
Melissa:Right.
Jam:Well, Melissa, thanks for teaching us, and thanks for being you know, wanting to bake us awesome goods. Listeners, if you guys have any ideas like candles, something very everyday in your life, but that has some really cool chemistry Underlying makings and mechanics and stuff like that. Please, we'd love to hear your ideas. Reach out to us on Gmail, Instagram, Twitter, Facebook at Kim for your life. We are that on all those platforms.
Jam:We'd love to hear your thoughts and ideas. If you'd like to help us keep our show going and contribute to cover the cost of making it, Go to kodashfi.com/chem for your life and donate the cost of a cup of coffee. But if you're not able to donate, you can still help us by subscribing on your on your favorite podcast app and rating and writing a review on Apple Podcasts. That also helps us to share chemistry with even more people.
Melissa:This episode of Chemistry For Your Life was created by Melissa Collini and Jarem Robinson. References for this episode can be found in our show notes or on our website. Jim Robinson is our producer, and I'd like to give a special thanks to s Navarro and Inhul who reviewed this episode.
