[not_a_frog]

Hi guys, got a few questions concerning thermochem and thermodynamics. Just a few hints would be great

First one:

The bond strengths of the following molecules have been determined spectroscopically. Find the molar enthalpies of formation of the corresponding free radicals (i.e. H from H2). T = 298K.

H-H(g) 436.0kJ/mol

What I have so far is this:

H=U+pV

pV=nRT

H=U+nRT

dH=dU+dnRT

And I would then plug in the bond strength values and solve for dH. Is this the correct way of going about it?

Second question:

Calculate the standard enthalpy of formation of propane gas from its elements at constant pressure using the data supplied for the following reactions at 298K and 1atm pressure.

Standard enthalpy of combustion of propane = -2220kJ/mol

Standard enthalpy of formation of water = -285.9kJ/mol

Standard enthalpy of formation of CO2 = -393.5kJ/mol

The chemical equation for this reaction would be C3H8 + 7O2 ---> 4H2O + 3CO2

I apply Hess' law and get standard enthalpy of formation of propane gas = (2220-1143.6-1180.5)kJ/mol

I'm just unsure as to whether I've done this correctly.

Any help/advice appreciated!