Find ΔHrxn for the reaction: N2O(g) + NO2(g)h3 NO(g) Use these reactions with known ΔH ’s: 2 NO(g) + O2(g)h2 NO2(g) ΔH = -113.1 kJ N2(g) + O2(g)h2 NO(g) ΔH = +182.6 kJ 2 N2O(g)h2 N2(g) + O2(g) ΔH = -163.2 kJ

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.