Chapter 6.5: Hess's Law: Finding ΔH of Any Reaction

Flashcards from Chapter 6.5 of Chemistry: The Molecular Nature of Matter and Change.

Hess’s law

This states that the enthalpy change of an overall process is the sum of the changes of its individual steps in ΔH

• Expressed as ΔH_overall = ΔH₁ + ΔH₂ + … + ΔH_n

• Used with equation manipulation

1. Identify the target equation and note the amounts of each product.

2. Adjust each equation with known ∆H values so that the target amount of each substance is on the correct side.

3. Add the adjusted equations and their resulting ∆H values to get the target equation and its ∆H.

How would I utilize Hess’s Law?

Use fractional coefficients or reverse the equation.

How can I manipulate a chemical equation?

State function

A property that depends solely on a current or instantaneous state of a substance