Suppose that a chemical equation can be written as the sum of two other chemical equations. If two reactions have AH values of -658 kJ and +458 kJ, what is AH for the reaction that is their sum?​

the answers would be

the first one and the second one

answer: atomic mass was originally used to arrange elements on the periodic table, but is no longer used to organize the modern version.

explanation:

originally atomic mass was used to arrange elements on the periodic table from left to right in a row. each column then shows similar properties of elements of a group.

in modern periodic table, the atoms are arranged in increasing atomic number. as atomic number represents the number of protons in an atom which is unique for every atom.