Don’t be a party pooper! Learn the science behind PARTY POPPERS! Because knowledge is a gift that stays after the confetti settles! So let’s ring in the new year with a talk about redox, thermodynamics, free energy, and confetti!
I don’t have any party poppers this year, but I did a couple years ago, so that’s where the pictures are from. Naturally, I wanted to know how they worked, so I looked into them (literally and figuratively) and want to explain it to you too.
The inside end of the string coming out of those party poppers is wrapped with a piece of paper painted with a tiny amount of gunpowder. When you pull on the string, it creates friction that produces heat energy that sets off a detonation reaction and the pressure produced pushes confetti out. Sometimes these poppers are called “champagne poppers” because of their shape. But that shape’s not just for show! Instead, the bell shape helps direct the force away from you. Of course, that’s only if you use them properly, so don’t point them at people, keep them away from your face (& especially your eyes) etc.
note: Some party poppers get rid of the explosives all together & instead rely on compressed air & a spring-loaded base, but I’m going to discuss the “OG” ones which use a gunpowder (sometimes aka “Armstrong’s mixture”) that’s a mix of potassium chlorate (KClO₃), antimony sulfide (Sb₂S₃), & phosphorus (P). It undergoes the overall reaction
28 KClO₃ (s) + 6 Sb₂S₃ (s) + 3 P₄ (s) -> 28 KCl (s) + 3 P₄O₁₀ (s) + 6 Sb₂O₃ (s) + 18 SO₂ (g)
This is a “redox reaction” and to understand what that means, let’s look closer at those chemicals. The chemicals in party poppers are made up of atoms, as are all chemicals, including water! (Remember “chemical” doesn’t mean bad!) Water is a chemical that is made up of 2 hydrogen atoms, and one oxygen atom (so dihydrogen monoxide or H₂O). The chemicals in fireworks involve things like potassium potassium perchlorate, KClO₄, which has one potassium atom, one chlorine atom, & 4 oxygens. ⠀
Atoms are made up of smaller parts called subatomic particles. There are 3 main ones – neutral neutrons and positively-charged protons hang out in a dense central core called the atomic nucleus. And whizzing around them in a cloud are negatively-charged particles called electrons. ⠀
The protons try their best to use the “opposite charges attract” thing to leash in the negatively-charged electrons whizzing around them. But they can only hold a certain number. And kinda like a dog walker trying to walk too many energetic dogs at once, the most energetic electrons, valence electrons, which are located furthest from the nucleus, are most likely to run away (or hook up with other molecules)⠀⠀
“Redox reactions” are chemical reactions in which molecules called reducing agents (reductants) give up some of their negatively-charged electrons (e⁻) & other molecules called oxidizing agents (oxidants) take them. To remember which is which, think OIL RIG: Oxidation Is Loss of electrons (e⁻) & Reduction is Gain of e⁻ ⠀
We’ve seen some important but “small-scale” redox reactions – like the reduction & oxidative reformation of disulfide crosslinks in your hair in perms http://bit.ly/cysteinecrosslinks or the reduction of water through electrolysis that creates the charge gradient needed for gel electrophoresis. http://bit.ly/2XMLMbG⠀
Party poppers are also based on redox reactions, but ones with a greater release of free energy (G). Energy is the ability to do work, which we obviously need for fire-works! (work is basically just thing-doing, often defined as the movement of matter – so, like pushing stuff, even on a super super tiny scale). And change in free energy (ΔG) is like a measure of chemical “drive.”⠀
I like to think of free energy as a sort of “couch shopping.” Say you’re sitting on a couch. It’s not a very comfortable couch; it’s cramped & hard so you’re squirming around a bit trying to get comfortable. There’s a more comfortable couch across the room, and when you’re in that couch you sink right in & can relax & stop squirming. Aaahhh…
BUT in order to get to the comfy couch you have to overcome your laziness & get up off the 1st couch. Whether it’s “worth it” depends on how much comfier the 2nd couch & this depends on how much less squirmy you’ll be there & how much you’ll be able to spread out.⠀
Similarly, whether a reaction will occur SPONTANEOUSLY depends on whether the products have more or less “free energy” than the reactants. We can think of this “free energy” (aka Gibbs free energy (G)) as a sort of overall “comfiness.” It takes into account squirminess (kinetic energy aka HEAT) in the ENTHALPY term (H) & spread-out-ability (randomness/freedom/disorder) in the ENTROPY term (S). ⠀
ΔG = ΔH-TΔS⠀
Δ (delta) means “change in” so this equation looks at DIFFERENCES in H & S between reactants (couch 1) & products (couch 2).⠀
Where’d that T come from? It stands for temperature & it takes into account the “mood.” ΔH & ΔS are “constant” because they’re calculated based on the reactants & products. But just like couch 1 & couch 2 don’t change, but when it’s hot, you care more about spreading out, at higher temps, ENTROPY becomes more & more important. (molecules want to spread out when they’re hot just like you!)⠀
NEGATIVE ΔG means products have LESS FREE ENERGY than reactants, so the “2nd couch is comfier” & the reaction is likely to proceed spontaneously. We call such reactions EXERGONIC.
POSITIVE ΔG means products have MORE FREE ENERGY than reactants, so you’ll have to really bribe it to go… We call such reactions ENDERGONIC⠀
NEGATIVE ΔH means products have LESS HEAT than reactants. This can only happen if reactants give up heat to the “surroundings,” and such heat-releasing reactions are called EXOTHERMIC ⠀⠀
POSITIVE ΔH means products have MORE HEAT than reactants. Which basically means reactants “stole” heat from “surroundings.” Such heat-absorbing reactions are called ENDOTHERMIC ⠀
NEGATIVE ΔS means the products have LESS FREEDOM/RANDOMNESS. This can come from having more and/or stronger bonds tethering the molecules together.⠀
POSITIVE ΔS means the products have MORE FREEDOM/RANDOMNESS. This can come from having fewer and/or weaker bonds tethering the molecules together, allowing them to move around more, which molecules like, remember. What they really like (you get a large positive ΔS from) is if you can go from a liquid to a gas &/or break up a big thing (which has limited motion bc it has to move as a group) into lots of smaller things which can move separately. ⠀
So, to summarize this thermodynamic mumbo-jumbo, reactions are more favorable if they let off heat (have a ➕ ΔH) &/or give the molecules more freedom/randomness (have a ➕ ΔS). BUT it’s the combination of those 2 (& temp) that’s the ultimate decider of whether a reaction will occur spontaneously (have a ➖ ΔG). ⠀⠀
Now that we’ve had this thermodynamic refresher, let’s get back to those poppers with those concepts in mind: ΔG = ΔH – TΔS where ΔH is change in enthalpy (heat), T is temperature, & ΔS is change in entropy (disorder/randomness).⠀
Popper reactions have a large (negative) ΔG (strong chemical “drive”) that’s coming from both enthalpy & entropy. ⠀
🔹as you might feel in your hand when you pull their string, poppers give off heat (are EXOTHERMIC). They have a large ➖ΔH, which makes ΔG more ➖
🔹poppers gain LOTS of ENTROPY when they “explode” (molecules get to go from confined in a shell to shooting off randomly, taking the confetti with them) AND this ΔS is multiplied by higher temperature (H). Which makes ΔG VERY ➖⠀
Result: the popper reaction releases lots of free energy (the reaction is very EXERGONIC). So, what *is* this reaction I’ve been teasing? Let’s look inside (one example, as there are many other chemicals that can be used)⠀
The overall reaction is:
28 KClO₃ (s) + 6 Sb₂S₃ (s) + 3 P₄ (s) -> 28 KCl (s) + 3 P₄O₁₀ (s) + 6 Sb₂O₃ (s) + 18 SO₂ (g)
KClO₃ acts as an oxidant – it gives oxygen (O) to the Sb₂S₃ & P₄ and takes electrons from them, oxidizing them & becoming reduced in the process.
Now let’s look back at our thermodynamic concepts to tease out why this reaction is favorable.
Let’s start by looking at those little letters in parentheses, which indicate the “state of matter” a molecule is in; “s” means solid, “g” indicates gas, “l” is liquid, etc. We can see that this reaction starts with all solids and ends up with ifferent solids AND a gas. Molecules in a gas have much more freedom than molecules in solids, so the products have a greater entropy, which, as we discussed, is one of the key drives for chemical reactions.
Because the gas molecules have more energy, they want to fly around, but the end cap’s in the way (who’s the party pooper now?…) BUT if enough gas molecules bang into it, the cap will come off & confetti will fly out! The confetti is still a solid, so individual atoms in it are stuck together, but, as a “group” they can get more “random” by uncoiling – so they do 🎉
In addition to this entropic gain, there’s an *enthalpic* (energy) benefit, so the reaction is EXERGONIC, meaning it gives off energy.
If it’s so favorable, why doesn’t it spontaneously “go off”? A couple reasons… Firstly, for any reaction you have to put in some energy to overcome the “activation barrier” – kinda like how it’s hard to overcome your laziness & get up off the couch, but once you do it’s easier to keep going, & once you’ve done what you needed to do you feel really glad you did it!
Additionally, for this particular reaction, you need to “free” the phosphorus from its polymeric chains. Elements (like carbon (C) & phosphorus (P)) can have different atomic arrangements called ALLOTROPES. http://bit.ly/carbonchemistryfranklin Just like diamonds & graphite are 2 allotropes of carbon, “white phosphorus” & “red phosphorus” are 2 allotropes of phosphorus and they have different properties.
WHITE PHOSPHORUS is 4 P molecules attached together in a tetrahedral conformation -> P₄
In RED PHOSPHORUS, some of those those tetrahedrons link together to form chains (polymers). The chains can have different lengths so red phosphorus is a variable mixture (as opposed to the “pure” white phosphorus).
White P is toxic & highly PYROPHORIC (it self-ignites upon exposure to air, so you have to store it under water). Red P is more stable than white P so you can let it “breathe” (& you can breathe a *little* easier…). This red form is what’s in the poppers.
BUT when you pull the popper’s cord it creates friction -> P molecules get more energy, start moving around more -> some of the tetrahedrons in the chain break apart to give you the more “burnable” white P -> it ignites & generates heat -> that helps the oxygen molecules break free from the KCl they’re attached to -> redox reaction drives on, producing more gas & energy until the fuel runs out
⚠️ There’s so little gunpowder in these poppers that they’re generally not considered “fireworks” & therefore have laxer regulation BUT still use caution & common sense when using them ⚠️
more on thermodynamics: http://bit.ly/thermodynamicsfreeenergy
#365DaysOfScience All 👉 http://bit.ly/2OllAB0