[hann]

 
Hey Everybody

Im having trouble getting this, I know the unit of enthalpy change is KJMol^-1.

So if you use you  will just get KJ. So you have to divide it by the number of moles of something... I'd assume for Formation you'd divide by the number of moles of what is formed, and for combustion you'd divide by the number of moles of the fuel?

But what do you divide it by the number of moles of when its just a 'normal reaction'? Is it the number of moles of all the reactants, or something else?

Thanks in advance

[tamim83]

Enthalpy is just the heat at constant pressure.  It has units of energy (J or kJ).  Chemists often want to know the enthalpy per mole.  For a reaction, you can calculate the enthalpy per mole of a specific reagent or product (like you do for a formation or combustion reaction).  You can calculate the enthalpy change for a specific reaction by using the tabulated formation enthalpies for each reagent or product, multiplying each value by the stoichiometric coefficient.