Enthalpy question?
1 Answer
No, it's not correct. Does carbonic acid dissolve in water (could it ever be a solid?), or does it decompose in water? Furthermore, is the second reaction balanced? (No, it is not. Where is carbon?)
The corrected reactions are:
"CaO" (s) + 2"HCl"(aq)->"CaCl"_2(aq)+"H"_2"O"(l), " " DeltaH=-194.2 " kJ"
"CaO"(s)+"CO"_2(g)->"Ca"color(red)"C""O"_3(s)," " DeltaH=-178.4 " kJ"
You should get
cancel("CaO" (s)) + 2"HCl"(aq)->"CaCl"_2(aq)+"H"_2"O"(l)
"CaCO"_3(s) -> cancel("CaO"(s))+"CO"_2(g)
"----------------------------------------------------------------------"
"CaCO"_3(s) + 2"HCl"(aq) -> "CaCl"_2(aq) + "H"_2"O"(l) + "CO"_2(g)
which is due to correcting and then reversing the second reaction mechanistic step.
The enthalpy of reaction then comes from the additive property of state functions:
DeltaH_1 + DeltaH_2 = DeltaH_(rxn)
And the second step was reversed, thus reversing the sign of its
color(blue)(DeltaH_"rxn") = -"194.2 kJ" + (-(-"178.4 kJ"))
= color(blue)(-"15.8 kJ")
