2C6H14 + 19O2 → 12CO2 + 14H2O How many atoms, total, are reacting in this equation?

Answer is: seventy eight (78) atoms in this reaction.

In this balanced chemical reaction there are twelve carbon atoms (from two molecules of C₆H₁₄), twenty eight atoms of hydrogen (from two molecules of C₆H₁₄) and thirty eight atoms of oxygen (from nineteen molecules of oxygen):

12C + 28H + 38O = 78 atoms total.