Chemical reactions may be classified into reaction 'types.' There are many such possible systems, but one way is to organize reactions according to whether materials are coming together, breaking down, or changing bonding partners. In a 1)______________________ reaction, two or more materials combine to produce a single product. In a 2)_____________________ reaction, one material is broken down into two or more products. In a 3)___________________ reaction, one element is replaced for another in a compound. Finally, in a 4)____________________reaction, two materials 'swap' bonding partners, to generate two new products