This happened last night. It’s particularly embarrassing because I have a science degree and was a Chemist earlier in my career, and had I read up more on epoxy resin before trying this project the outcome we experienced would’ve been obvious.
My sister-in-law is getting married in June. I offered to make decorations, and one thing she’d like is large letters for her and her husband to go on the wedding table (P&J). I figured letters around 16-18 inches tall would be pretty good and something like 2-3 inches deep- I have recently started making resin art (very recently) and I had a vision of making them out of resin, using fairy lights embedded with fresh white roses. I’ve seen a hot dog encased in resin, and I’ve seen large projects like tables with resin- so I figured no problem. I could not find a silicone mold for letters anywhere near that tall for resin making (which should’ve been a clue), but my friend works in a printing shop and has access to a router for straight lines and tons of materials we figured we could make work. So she was awesome and brought them over last night, we sprayed the snot out of them with mold release because we wasn’t sure if the mold materials were porous that might stick to the letters. We then proceeded to start with the letter P as our test letter because it was the easiest mold to re-make if needed- and we have until June to figure it out. We got the fairy lights in, and chopped the heads of the roses off so they’d fit. Here's the fuck up: we added roughly a half gallon of resin very quickly. We mixed in small 8 oz cups the two parts of resin and added glitter. The roses kept bobbing to the top inside of the mold so eventually we put a thick piece of laminate cover sprayed with mold release to push the roses down and keep them submerged best we can. I noticed a slight burning smell, but assumed it was from the blow torch that we used to get some of the bubbles out.
My friend and I are sitting at the table feeling accomplished and optimistic our project worked decently well- just worried about how the resin will come out of the mold once hardened. I set my hand on the laminate cover and notice it’s HOT! Like very hot. I quickly take the laminate cover off and see the epoxy is smoking and the roses are looking burnt- it smells like a combination of rotting pumpkin cooking and burning plastic.
Thankfully we live in Michigan and are surrounded by 3 feet of snow. We took the whole project outside and dropped it o... keep reading on reddit ➡
Why are chemical reactions that cause a drop in temperature of the product endothermic reactions? Aren’t they “letting out heat”, leading to a decrease in temperature?
Cuz you always keep me warm
Older spacecraft (like the Apollo missions) used Lithium Peroxide to sequester Carbon Dioxide in the spacecraft cabin. The result of the reaction is Lithium Carbonate and Oxygen. I was wondering if the reaction was Endothermic or Exothermic, and if possible if anyone knows the joules of heat generated or consumed by the reaction.
Thanks in advance for your help. I’m a high school chemistry teacher and there’s a bit I’m unclear about.
We are learning about collision theory in class. In summary, any factor which increases the number of collisions increases the rate of the reaction. Right?
However, the fact that equilibrium in a reversible reaction is shifted towards the endothermic side when temperature is increased suggests that, at the very least, an exothermic reaction benefits less from increased average kinetic energy of atoms. Why?
Some chemistry students (including those preparing for the MCAT) understandably have the misconception that because exothermic reactions RELEASE heat, they must get colder. This stems, I think, from a misunderstanding of what it means to “release” heat.
It is not that some of the heat already in the system is somehow ejected. Rather, in an exothermic reaction, chemical energy is CONVERTED to heat. In other words, energy that WASN’T in the form of heat before the reaction now BECOMES heat. The heat produced causes the temperature (ie, kinetic energy) of the molecules in the system to rise.
Another potential source of confusion is that many texts say the heat goes from the system into the surroundings. Makes it sound like the surroundings get hotter and the system gets colder. But consider an individual molecule at the center of the beaker where the reaction is taking place. Its surroundings ARE the adjacent molecules in the system.
So this central molecule, upon “releasing” heat (see above) causes those adjacent molecules to get hotter. Meanwhile the adjacent molecules are also releasing heat, causing the central molecule (and other nearby molecules) to get hotter. The molecules at the edge of the beaker send the newly produced heat into the beaker walls, which in turn transfer some of that heat to the surrounding air. So exothermic reactions cause the system AND the surroundings to get hotter.
A few illustrative examples that you could potentially try at home.
Consider the combustion of carbon:
C(s) + O2(g) --> CO2(g). ∆H = -393.5 kJ/mol, meaning this reaction is highly exothermic. This is the reaction that happens when you burn charcoal. After you’ve burned it, are the embers hotter or colder than they were before you burned them?
NaOH(s) + H2O(l) --> NaOH(aq). ∆H = -44.5 kJ/mol, so it’s exothermic. If you have access to a lab, chances are you have some NaOH for adjusting the pH of different buffers and such. Ask if you can make the next batch. See what happens to the temperature of the water once you add it to the solid NaOH tablets. You can touch the glass (carefully) or just use a thermometer to monitor temperature over time.
I'm working on a paper on a material that was annealed at different temperatures and and the DSC graph shows a major peak between the temperature of sintering and the temperature just before it. However, when searching sources as to whether sintering is endothermic or exothermic, I came up empty handed.
I believe sintering in general is exothermic, because it's spontaneous (ΔG<0) and results in lower entropy (ΔS<0), so it must release energy (ΔG=ΔH-TΔS, so ΔH<0). However, I'm not sure my thought process is right since sintering is not really a chemical process, so I don't know if Gibbs Free energy actually applies. Help, please?
The solubility of a gas in a liquid decreases with the increase in temperature.Why? Also, why is it an exothermic process? Thanks in advance!
I think they always increase the entropy because they add heat to the surroundings in the form of kinetic energy.
in the Gibbs free energy, it is possible to have negative enthalpy (exothermic) AND negative entropy (less entropy). That type of reaction would be favorable only at low temperatures. It seems therefore that an exothermic reaction could DECREASE the entropy.
So I don't understand, maybe I'm mixing up things.
Hello, as you can see from the title, I have a question about heating equilibrium mixture. So according to my textbook, when you heat an equilibrium mixture, more endothermic reaction will happen to reduce the temperature (or work against the change in the environment). However, I don't really understand how endothermic reaction will reduce the temperature of the mixture. Exothermic means that heat or energy is released, therefore shouldn't exothermic reaction reduce the mixture's temperature? Even though I like chemistry, but this topic always confuses me. I'd appreciate a lot if you could tell me the easiest explanation you can come up with me, as I haven't studied many chemistry yet.
I'll be basing this off the equilibrium R-OH + H+ <==> R-OH2+ :)
From what I understand, bond making processes are exothermic because energy is released when bonds are formed, and an additional O-H bond is formed in the equilibrium here, thereby making it exothermic. Since -OH alone is a poor leaving group and protonating it makes it a better leaving group therefore making it more reactive, wouldn't that then put R-OH2+ at a higher energy level than R-OH? (If we were drawing an energy diagram)
But if the more reactive R-OH2+ is at a higher energy level then that means it must be endothermic on that diagram?
I'm really confused, hopefully someone can clarify this for me :)
i.e If an alcohol is halogenated into a alkyl halide, would it be exothermic or endothermic? (Assuming there's no supporting data) Since the C-Cl bond is weaker than the C-OH bond, I imagine it would be exothermic but I'm not sure if this is the correct reason why or not. But since -Cl is a better leaving group than -OH, which itself needs to be protonated to -OH2+ to leave C, wouldn't the alcohol be at a lower energy level than the alkyl halide, making it endothermic?
Sorry if my wording is confusing, it's been a while since I covered this topic lol
I'm trying to understand/teach myself about entropy but most questions I look at to try and understand already have the values given
How could I find these values myself to create a calculation?
I found something called a data booklet which gives me lots of information, one of which is 'electrochemical series: standard reduction potentials'.
Is this the correct data to use?
E.g. if I want to work out the entropy change of a reaction involving sodium, do I use this value (-2.71) for sodium in the calculation?
Or am I using the wrong values?
Still trying to piece everything together/understand as I go along.
Thanks for any help
So... Here's the thing, people like to think of themselves as rational decision makers installed in meat machines that obey every order. Computers grown to command their bodies, but the truth is we're more like the supervisors office, up on the gantry overlooking the whole chemical plant.
Oh sure, we have a good idea of what goes on, where specific things happen and when and how much they need, and will produce; but it's a whole lot of chemistry and we are not in complete control.
Things can go wrong, a catalyst performs too well, an inhibitor enzyme breaks down in the heat, and the brain has to retroactively explain why it decided to throw a punch when "we were just talking".
I'm no doctor, hell, I've failed out of college 3 separate times. just never learned to live with inefficient processes , I guess. I didn't react well to the pressure, maybe.
I don't consider it a wasted time though. I learned how things work, I learned how people work but never had anything to show for it, except friends.
My point, when mentioning all this is: when you put yourself in a bad situation, and your brain knows it has to get it out again or there will be consequences, it's like that supervisor, in that chemical plant, turns all the pipes open, sets all the reactions in process, as hard as it can.
And if it works? Well then the brain learns that maybe next time it'll work again. Again and again, the cycle repeats, desperation, panic, anxiety, a veritable chemical bath, a storm of reagents, and the relief and bliss of escape.
Some folks think you can talk your way better, like words can release just the right chemicals to break the bonds of this repeating solution.
But words have no atomic weight, they have no free electrons to give.
Others think they can throw a random pile of powders into the tanks and hope the reactions will balance out. I sympathize with the thought, but distain the work ethics; it could work if you examined every process, used exactly the right compounds, and delivered them at exactly the right point at exactly the right time.
they never do. They just chuck a handful in and hope for the best.
Sloppy, to my mind.
I found a fix. Of a sort. I say 'found' because... I did not manufacture or synthesise anything. A system built into the plants initial design, that seems to have gone mostly unused just... turned itself on. Maybe it would be more accurate to say it found me.
I had dug myself deep in another cycle. Work has give... keep reading on reddit ➡
I was going through some literature, stumbled upon one great diagram.
Would be great if anyone has come across some more of this, may be some reference material.
Hello, I have been researching for hours and cannot figure out why compounds such as calcium chloride are exothermic while potassium chloride are endothermic. Any resource I find does not tell me WHY, just that it is endo/exothermic. I would appreciate any bit of help in understanding WHY.
Furthermore, I have also yet to find any resource relating to the amount/mass of such compounds and how it relates to the temperature change. Is there any scientific reasoning why if I put more calcium chloride in water the water would more hotter/warmer? I am completely lost in finding out the scientific reasons on WHY it is exothermic in the first place and why the temperature change would differ based on the mass dissolved. It seems so logical yet there is no scientific reasoning I can find.
I would appreciate any resources, books or answers to these questions! Thank you!