Sagot :
There are several reasons for me:
First, everything you'll ever see is made of chemicals. EVERYTHING. Makes it worthwhile to want to understand it a bit, doesn't it?
Second, there's the knowledge that, give us a target structure, and enough time, and we'll make it. Some of them will require dozens of years and people, but we'll get there eventually (see the synthesis of vitamin B12 by Woodward and Eschenmoser, for example). Then the fun begins, because we'll look for ways to do it better, on larger scale, cheaper, with less toxic reagents, etc… so many problems to tackle, so many challenges to overcome, and nothing beats the feeling of succeeding in those things. The engineers must know this…
Third when I was a kid, I played with Lego. Now my building blocks are molecules, but the fun you can have in combining them in new and interesting ways is pretty much the same.
Fourth, and this is quite personal, I have a good memory, and I feel that this gift is very well used in chemistry, much better than in other sciences, which is rewarding.
Fifth, the experiments. It is really easy to set up an chemistry experiment, much easier than in physics or biology for example. My part of chemistry, synthetic chemistry, is fundamentally experimental. And I like that a lot, I can get answers to my questions very fast.
Sixth, the challenges again. You want to change the world? There is a field in chemistry that will allow you to help in a very tangible way: cleaner energy/ energy storage? Material chemistry is needed, and inorganic chemistry. Medicine? Try medicinal chemistry. Environment? Treatment of waste is a chemistry problem, just as better polymers, cleaner synthesis of commodity chemicals etc… World hunger? Designing new, safer, cleaner pesticides is done by chemists, better fertilizer as well. Note that you will not change the world by yourself, but no one does these days. I expect working on new batteries is much like working as an engineer on an electrical car, or a new rocket design: what YOU do is not flashy, but you participate in an endeavour that, if successful (and it will be in the end), will change the world for the better. For example: if you manage to replace a toxic chemical with a non toxic one in a specific synthesis, it might take years before that change is implemented in chemical plants, but when it is, you will have made the world a cleaner place. Not by much, but it all adds up…
Chemistry is a dirty industry, but it does not have to be, and the only way to make it cleaner is to get to work and find better ways to do chemistry so it necessitates less toxic chemicals, generates less/more benign waste, etc… whether by finding a new reagent/reaction/catalyst, applying those to real world synthesis, or implementing them on industrial scale. That's how you change the industry: from the inside, by making it more efficient. Here is an example: oxidations used to be done using highly toxic chromium oxides, those that Erin Brockovich fought against. Now? Whenever possible, there made using bleach… all thanks to chemists from research labs to the plant scale.