First, we construct the reaction equation:
Na₂SO₃ + 2HCl → 2NaCl + SO₂ + H₂O
H₂SO₃ is formed as an intermediate but decomposes to water and SO₂ gas.
“Bonding molecular orbitals are formed by... in-phase combinations of atomic wave functions, and electrons in these orbitals stabilize a molecule.”
add up the mass of protons and neutrons