Summary Hess’s Law notes

HESS 'S LAW
& STANDARD ENTHALPY OF FORMATION


standard enthalpy .
enthalpy change measured at 100 kPa

change Of formation
•

and a
specified temp ( usually 298K ) ,




( Df H°) when one more of a substance is formed
from its elements in standard states .




:
formation of
CH4
-




c t / H2 →
CH4
( s)
(
g) (g)
(
graphite )

(a CO3
-




Ca t C 1-3-202 →
Call }
(s ) (s) (
9' CS )
(
graphite )

HESS 'S I.AW
The enthalpy independent of path taken in
change of a reaction is the

converting reactants into products , provided the initial and final conditions

are the same in each case .