Enthalpy
MCAT glossary · Chemical & Physical Foundations of Biological Systems
Definition
The heat content of a system at constant pressure, symbol H.
Enthalpy in plain English
Enthalpy (symbol H) is basically the total heat energy stored inside a reaction or system when the pressure stays constant — which is the normal situation for anything happening in an open beaker under the sky's steady push. You rarely care about the raw number; what matters is the CHANGE, Δ H: if a reaction gives off heat (feels warm, like a hand-warmer) Δ H is negative, and if it soaks up heat (feels cold, like an instant cold-pack) it's positive. So think of enthalpy as the reaction's heat budget — the ledger of heat flowing in or out.
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