A________happens when two subtances are combined together and change into another subtance.A______is anything that is made up of "stuff" and takes up space.it might be in the form of a solid,a liquid,or a gas.Sometimes when two or more subtances are mixed together,a_______occurs and another subtance is created.this is called a______._______may form,_________may be produced,and_______may change.these types of changes indicate that a chemical reaction has occured.but some subtances when mixed together produce no chemical reaction