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The concept of standard enthalpy of formation and provides a formula to calculate it. It also includes an example calculation for the standard enthalpy of formation of CS2 (l) using the given data for CH4(g), O2(g), CO2(g), and H2O(l).
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Standard enthalpy of formation (ΔH
0 ) is the heat change
that results when one mole of a compound is formed from
its elements at a pressure of 1 atm.
SATP: Standard Atmospheric Temperature and Pressure
o C ( 298K) P = 1 atm
f
The standard enthalpy of formation of any element in its most
stable form is zero.
Calculate the standard enthalpy of formation of CS 2
( l )
given that:
4
(g) ΔH
0 = -74.4 kJ/mol f
4
(g) + 2O 2(g)
2(g)
2
O( l )
2
(g) ΔH
0 = 0 kJ/mol f
2
(g) ΔH
0 = -393.5 kJ/mol
f
0
r
n ΔH
0 (products) f
= Σ^ n ΔH
0 (reactants) f
0
r
0 (CO 2
f
0 (H 2
0 (CH 4
0 (O 2
f
f
0
r
[ 1 (-393.5kJ/mol )+ 1 (-285.8kJ/mol)]
-[ 1 (-74.4kJ/mol) + 2 (0kJ/mol)]
2
O(g) ΔH
0 = -285.8 kJ/mol
f
f
0
r
0
f
2
2(g)
0
f
2(g)
0
f
2
(g)
