state and explain hess's law of constant heat summation with example
Answers
Answer:
Hess's law of constant heat summation:
The law states that the change in enthalpy for a reaction is the same whether the reaction takes place in one or a series of steps. The Hess's law can also be stated as the enthalpy change for a chemical reaction is the same regardless of the path by which the reaction occurs.
For example, consider following two paths for the preparation of methylene chloride
Path I :
CH
4
(g)+2Cl
2
(g)→CH
2
Cl
2
(g)+2HCl(g)ΔH
1
0
=−202.3kJ
Path II :
CH
4
(g)+Cl
2
(g)→CH
3
Cl(g)+HCl(g)ΔH
2
0
=−98.3kJ
CH
3
Cl(g)+Cl
2
(g)→CH
2
Cl
2
(g)+HCl(g)ΔH
3
0
=−104.0kJ
Adding two steps
CH
4
(g)+2Cl
2
(g)→CH
2
Cl
2
(g)+2HCl(g)ΔH
0
=−202.3kJ
Thus whether we follow path I or path II, the enthalpy change of the reaction is same. ΔH
1
0
=ΔH
2
0
+ΔH
3
0
=−202.3kJ
Explanation:
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