We have been working on this problem for two days straight, and cannot figure out our error. Here is the problem we are given:
Calculate the standard enthalpy of formation for the reaction HCL (g) + NH3 (g) ---> NH4CL (s), given the following thermochemical equations:
H2 (g) + Cl2 (g) ---> 2HCL (g), standard enthalpy of formation: -184kJ (-92kJ/mol)
N2 (g) + 3H2 (g) ---> 2NH3 (g), standard enthalpy of formation: -92kJ (-46kJ/mol)
N2 (g) + 4H2 (g) + Cl2 (g) ---> 2NH4CL (s), standard enthalpy of formation: -628kJ (-314kJ/mol)
It wants us to combine the equations using Hess's Law to arrive at the desired equation. We did so, and we arrive at the desired equation given above ( HCL (g) + NH3 (g) ---> NH4CL (s) ). However, the number we have arrived at time and time again (-176kj/mol) is not the accepted standard enthalpy of formation for NH4CL, -314.43kJ/mol.
Someone please show us our error before we bash our head against the wall any further! Thanks!
Edit: Note, the book that gives the problem lists the answer we get (-176kJ/mol) as correct. We are looking for why this is not the accepted value.