Kirchhoff's Law (thermodynamics), change in heat capacity

[pillanoid]

Homework Statement

Calculate the standard enthalpy change ($\Delta H$) at 25 degrees Celsius and 927 degrees Cesius for the reaction,
WCl4(g) + CH4(g) = WC(s) + 4HCl(g)

Data:

WCl4(g): $\Delta H298$ = -336 kJ/mole; Cp (heat capacity at constant pressure) = 105.6 J/mol*K
HCl(g): $\Delta H298$ = -92.3 kJ/mole; Cp = 30.5 J/mol*K
CH4(g): $\Delta H298$ = -74.8 kJ/mole; Cp = 59.1 J/mol*K
WC(s): $\Delta H298$ = -40.2 kJ/mole; Cp = 46.5 J/mole*K

Homework Equations

$\Delta H(\text{final temp}) = \Delta H(\text{initial temp}) + \Delta Cp(\text{Tf - Ti})$
$\Delta Cp = \Sigma Cp(\text{products}) - \Sigma Cp(\text{reactants})$

The Attempt at a Solution

This is a take-home test, so it doesn't feel right getting help with the actual answer, but I have some specific questions I hope can be clarified for me:

1.) When calculating $\Delta Cp$, do you multiply each component by the number of moles involved? For instance, for the HCl factor in $\Delta Cp$, do you multiply Cp for HCl by 4? It seems like you should, but Cp stays in the same units, so the moles wouldn't cancel.

2.) Can I apply the equation for $\Delta H$ (of reaction at 927 degrees Celsius) as I have written above (as in, is it applicable as is, or do I need to do further analysis of this specific situation as Kirchhoff's Law applies?

Thanks!

 

[Astronuc]

These notes should help.
https://chem.libretexts.org/Bookshe...nergies_and_Potentials/Enthalpy/Kirchhoff_Law

Note that the enthalpy change values and heat capacities are given on a per mole basis and one should use the number of moles of products or reactants.

One would expect that examples of such a problem are given in one's text or class notes.