I decide 30 years ago that I had to tell my freshers this because they chose the subject without fully realising what the subject was about.

Chemistry . It uses two or more substances to first investigate the nature (property) of that unique (and pure ) substance and then by experiment find how it changes to one or more completely new substance(s) with a completely different nature (set of properties). BTW you are a complex mixture of substance and you cannot stay alive without doing chemistry. NB Best done with a few actual demonstrations of dramatic change. e.g bangs

In the romantic context? If you come together and together you make a new "substance" - (Mood, behaviour pattern, way of living) something that never existed before and would not exist without the other person then you have CHEMISTRY. Good luck with your experiments!! sometimes the new substance is a baby with appearance and traits coming from both partners

Just like pain, you knows it when you feels it.

Chemistry is nature's trick to enhance procreation. Life abounds with fecundity!

When you get horny when you see them.

Not easily definable. It has to do with most or all of the 5 senses, each excited and operating independently, as well as in-tandem with the brain, which gets washed in yummy chemicals that make us happy. It's more instinctual to start and is a feeling quite seperate from lust. It also has to do with not just wanting what you want, but wanting the the other to feel the same, but it's not quite love, yet. And chemistry is a TWO-way street. If it's just one-way, then it's just lust, or something different, which won't make the other party so happy. It's a little like an orgasm in one sense... hard to describe to someone who has never felt it, but we all know it once we have. Good chemistry and orgasms both send good tingles up and down the body.

If you don't know whether or not you have chemistry with someone, then you don't.

I think it the words women use to give me the brush off, you are a great guy, but I don't feel any chemistry, or the chemistry is not right. What they mean is
you are fat
I don't like red hair
I just met a guy with a porsche.

Pher·o·mone

plural noun: pheromones
a chemical substance produced and released into the environment by an animal, especially a mammal or an insect, affecting the behavior or physiology of others of its species.

Chemistry is physical attraction, emotional bond, sexual , and just wanting to be with that one person and no one else.

Either both like each other's company or don't.... There you go, that's all the chemistry

I get lust and chemistry confused in my mind, working on that with my psy doc. My friend used to call it a 'rut state'.

If it is there, you will know. It is not rocket science.

Romantic chemistry is just a hormonal reaction to the presence of a combination of pheromones that appeal to the individual's genetic sense of good breeding material. It could mean very little when defining what constitutes a successful relationship. But it sure does feel good.

Oh the chemistry is the easy part. Ya spark!!!! It's the long term respect for the differences of each other. My and I were so good together sexually but in the we just could not do right by each other. He needed to cheat and steal my identity and I needed to not live in chaos.

Im not sure it could be specifically defined. It could mean different things for different people. Im not even sure I could put into words what it is for me. I just know when its there.

If it is there, you want need someone to point it out to you! It is similar to what a magnet does...it is so powerful you will be, almost forced...to rip yourself away! Now, when it happens in old age, it is a bit more manageable! Lol

If one has to ask, there probably isn't much there.
It seems to be characterized by unexpected comfort in another's presense, ease of conversation, and a yen to re-establish the connection.

Idk? I've never felt a chemistry bond with any ex bf's.

Blah becomes magically interesting when there is chemistry present between people. Ordinary things become unordinary. Most importantly, it's not one sided. Both people must feel as though what is occurring is due to a certain chemistry that comes when these two specific persons are paired up and interacting with each other.