Is mass conserved in chemical reactions?

Mass is not conserved in chemical reactions. The fundamental conservation law of the universe is the conservation of mass-energy. This means that the total mass and energy before a reaction in a closed system equals the total mass and energy after the reaction. According to Einstein's famous equation, E = mc2, mass can be transformed into energy and energy can be transformed into mass. This is not some exotic process, but in fact happens every time there is a reaction. Mass is therefore never conserved because a little of it turns into energy (or a little energy turns into mass) in every reaction.

b c a d mark me

"1. it should be, it has been for about 20 years, and it's really not much different in the end than breeding animals to have particular traits. there are always concerns about genetically engineered animals/plants affecting the environment in unexpected negative ways, but i can't think of an example where the fears didn't turn out to be baseless.  

first, as you point out, it would be a great advance in pharmacology, to be able to tailor drugs and their doses to me. the pros involve better medical treatment. the cons involve privacy issues like insurance companies denying coverage to people with genetic risk factors. looking at dna markers wouldn't affect the frequency of genetic diseases, but it would allow detection of them earlier. and ok, actually i suppose that if people used this information to avoid having children with genetic diseases, some might decrease in frequency."