Consider the thermochemical equations
(1) CaCO₃(s)+2 HCl(aq)→CaCl₂(aq)+CO₂(g)+H₂O(l) ΔH₁=−80 kJ
(2) CaCl₂(aq)+H₂O(l)→CaO(s)+2 HCl(aq) ΔH₂=+200 kJ.
A student added the equations but failed to cancel 2 HCl(aq) and H₂O(l), writing
CaCO₃(s)+H₂O(l)→CaO(s)+CO₂(g)+H₂O(l) ΔH=+120 kJ.
List the species that should have been canceled and give the corrected overall reaction with its ΔH (in kJ).