Lesson 6 + 7 - Hess's Law of Summtion (copy)

Hess’s Law of Heat Summation

For any reaction that can be written in steps, the standard heat for a reaction of the overall reaction IS THE SAME as the sum of the standard heats of the indiviudal steps

Definition of a standard heat of formation

The standard heat of formatiomn is a form of enthalpy

The amount of heat absorded or evolved when 1 mole is formed at spefically 25 degC at 1 atm. (standard conditions)

To determine the standard heat of formation to use it for determining deltaH for a given reaction use:

ΔHreaction=ΣΔHof(p)−ΣΔHof(r)

Delta Hformation cannot be

negative

Find the heat of formation values form chart

and plug it in with their according element/compoound