Chem Help ! Confused about Enthalpy

Question

Using standard heats of formation, calculate the standard enthalpy change for the following reaction. 

Fe(s) + 2HCl(aq)FeCl₂(s) + H₂(g)

Answer 1

I'll do this for you:

You need to determine heat of formation (Hf) for each of these things. For example, Hf for H2 is Zero (0) because it is the natural, elemental form. Same thing for Fe(s), However, HCl and FeCl2 are not the "elemental" forms. They have Hf (enthalpy). So, determine the enthalpy for each (should be in your book, or online if you need to search). Once you have the standard enthalpy, you multiply by the coefficient. So, for HCl, the coefficient is 2. You multiply the heat of formation by 2. Then, you subtract, Products (right side) - Reactants (left side) to get the standard enthalpy change.

Hf of Fe(s) = 0

Hf of H2(g) = 0

Hf of HCl = ?

Hf of FeCl2 = ?

Next step

PRODUCTS - REACTANTS

[Hf of FeCl2] - [2 * Hf of HCl]

The reason it is P - R is because since products are the end, you subtract the beginning for the change in enthalpy. E.g. It was 45 degrees earlier, now its 60, the change in temperature is 15 (60-45, end-beginning)