How much does the copper pipe weigh if it absorbs 8245.31 J of energy as it is heated from 12.7 C to 45.9 C

They are all decomposition reactions.

Idont know. if you want an answer you need to give us some context dude.

It is a mixture. simply put, a compound must be pure, that is, of only one chemical structure and composition. a mixture is made of different chemical substances (i.e. elements, molecules, compounds) that are not chemically bonded to each other, but instead physically grouped together, as in the case of gasoline (a homogeneous solution).