define hess law

. 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

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

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define hess law

Hess’s Law