What is chemistry? Neil deGrasse Tyson and comedian Chuck Nice take fan questions on exothermic reactions, PFAS, ice cream, sugar, fire, and more with Kate Biberdorf, aka Kate the Chemist. Fundamentally, what is a chemical reaction? Kate breaks down the basis of chemistry, how it overlaps with thermodynamics, and exo- versus endothermic reactions. Why is Gallium a liquid in the US but listed as a solid in the UK? Plus, Kate schools Neil on how adding salt to ice can help you make homemade ice cream. If hydrogen and oxygen are both flammable, why isn’t water super flammable? We discuss how chemists predict a molecule’s properties. Learn about activation energy and how elements manage to even bond with each other. We break down combustion reactions and why sugar gets hard when you heat it to a certain temperature. Are PFAS as dangerous as we think they are? We explain what PFAS are and what makes them problematic for our health. What gives colors to the elements? We talk about quantum dots, visible light, and what happens when you put sodium in water. All that, plus, what makes oxygen so special? Thanks to our Patrons Mark Baum, Ezequiel Adatto, James Wright, Vector169, Ray Rimes, Christopher Haws, Ruben Ramen, Kim Fletter, Daniel Brown, and Joy Pinero-Deniz for supporting us this week. NOTE: StarTalk+ Patrons can listen to this entire episode commercial-free. Check out our second channel, @StarTalkPlus Get the NEW StarTalk book, 'To Infinity and Beyond: A Journey of Cosmic Discovery' on Amazon: https://amzn.to/3PL0NFn Support us on Patreon: https://www.patreon.com/startalkradio FOLLOW or SUBSCRIBE to StarTalk: Twitter: http://twitter.com/startalkradio Facebook: https://www.facebook.com/StarTalk Instagram: https://www.instagram.com/startalk About StarTalk: Science meets pop culture on StarTalk! Astrophysicist & Hayden Planetarium director Neil deGrasse Tyson, his comic co-hosts, guest celebrities & scientists discuss astronomy, physics, and everything else about life in the universe. Keep Looking Up! #StarTalk #NeildeGrasseTyson 00:00 - Introduction: Kate the Chemist 5:57 - What is a Chemical Reaction? 10:29 - Endothermic v. Exothermic Reactions 15:14 - Can You Predict a Chemical’s Properties? 18:34 - What is the Role of Activation Energy? 23:51 - The Chemistry of Candy 29:38 - Are PFAS as Dangerous as We Think? 34:05 - What Gives Things Color? 36:17 - Why Isn’t Water Flammable? 39:04 - Seeking a Scientist 40:53 - A Cosmic Perspective