Question

short question
why standard
state is used
for enthalpy
changes?

Explanation:

Enthalpy is a state function, but its absolute value cannot be measured directly. Standard state (defined as 1 atm pressure, 298 K temperature, and pure substances in their most stable form) provides a universal, consistent reference point. This allows scientists to calculate and compare enthalpy changes (like reaction enthalpies, formation enthalpies) across different reactions, substances, and experimental setups reliably, ensuring results are reproducible and comparable globally.

Answer:

Standard state is used for enthalpy changes to provide a consistent, universal reference point. Since absolute enthalpy cannot be measured, this defined set of conditions (1 atm, 298 K, pure stable substances) allows for accurate, reproducible calculation and comparison of enthalpy differences between reactions and substances.