Use the information below to calculate the ∆H for this reaction: NaOH(s) + HCl(g) → NaCl(s) + H2O(g) AHreactants = -519.0 kJ/mol AHproducts = -652.8 kJ/mol O +133.8 kJ/mol 0 -133.8 kJ/mol 0 -1171.8 kJ/mol O +1171.8 kJ/mol​

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.

every chemical equation adheres to the law of conservation of mass, which states that matter cannot be created or destroyed. therefore, there must be the same number of atoms of each element on each side of a chemical equation.