I'm gonna parrot what most of the people here say, yes love is a chemical reaction in the brain, but so is every single thing we are able to perceive. That of course includes all emotions that we feel, every thought we have, and really even our ability to perform scientific experiments and observe the results. In fact everything we experience is a chemical reaction in the brain, because that's how the human brain works. So everything we see, hear, feel, taste, smell, or experience in anyway is the result of a chemical reaction in the brain, because that's how our brains process the universe around us. Our entire lives are just series complicated chemical reactions that we define as being "life", as is the life of anything we classify as "living".