Chemistry / Unit 4 Chem 0681 short lesson, about 20 seconds
Sign Convention for Enthalpy Change
Captions available
The idea
A negative enthalpy change marks an exothermic reaction; a positive one marks endothermic, and reversing flips this sign.
In practice
Hydrogen and oxygen forming liquid water release 286 kJ per mole, so ΔH is −286 kJ; decomposing water back carries ΔH = +286 kJ.
Where people slip
"The reaction gets cold, so it releases heat" inverts this convention — a falling temperature marks endothermic, a positive ΔH.
Your place on the trail
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