Everything Is Measured From The Elements

You'll learnto measure compounds against an elements-at-zero baseline, then take products minus reactants.

You cannot measure a substance's enthalpy, only a change in it. So chemistry picks a zero and measures everything from there, and the zero it picks is the elements themselves. After that, any reaction's ΔH° is one subtraction. Twelve short steps; press Next for each one.

12 STEPS · 6 QUICK CHECKS · ΔH° = ΣnΔH_f°(products) − ΣnΔH_f°(reactants) · v4

elements at zero · every compound measured from there

Before you start

What you're looking at

One mole of water being built from its elements: hydrogen and oxygen on the ink line, water far below it.

The question

Is the zero beside O₂ in the table something somebody measured, or something we chose?

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