8.99 Enthalpies of Formation [ENDORSED]

[MCracchiolo 1C]

In the solution manual for 8.99, the calculated reaction enthalpy is found by the equation

Delta H (RXN) = -153.89 +2(-167.16)-2(-167.16)-0 = -153.89 kJ/mol

...but the balanced chemical equation is 2HCl(aq)+Zn(s) --> H2(g)+ZnCl2(aq)

Shouldn't the standard enthalpy of formation for H2 gas be 0? And why is the enthalpy of formation for Zn2+ used for ZnCl2?

[Curtis Tam 1J]

I believe the solution manual says H2 is zero right? The enthalpy of formation for Zn2+ is used because ZnCl2 dissociates into Zn2+ and Cl- ions.

[Esin Gumustekin 2J]

For this question, how do we know that Zn is 2+. It is not stated anywhere in the problem so how could we determine this?

[Chem_Mod]

ZnCl₂ and halogens are always -1.
Therefore Zn must be 2+.