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from KENDRIYA VIDYALAYA NO 1, asked a question
Subject: Chemistry , asked on 26/9/12

# define hess law

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. Hess ' Law states that the heat evolved or absorbed in a chemical process is the same whether the process takes place in one or in several steps. This is also known as the law of constant heat summation. To illustrate Hess 's law, the thermal equations and the energy level diagrams are shown below

Thermal equations Hess 's law energy level diagram
• A + B = AB, dH 1
• AB + B = AB2, dH 2
then,
A + 2 B = AB2, dH 1 2 = dH 1 + dH 2
rnrn    ======= A + 2 Bn     |   | dH 1ndH 1 2 | ===== AB + Bn     |   | dH 2n    ======= AB2n
rn

hope it will definetly help u...

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