Standard state

[ng1D]

What is the standard state of a substance and how do I know if a substance is in its standard state?

[DanielTalebzadehShoushtari2A]

The standard state of a substance is its most stable form at 1 atm and (usually) 25 degrees Celsius. In standard state, gases are at 1 atm, solutions are at 1 M (and also 1 atm), liquids/solids are assumed to be pure, and elements are in their most stable phase.

[Wilson 2E]

The standard state is the phase a compound is in at standard conditions (25 C, 1 atm), and is typically indicated for an element on the periodic table.

[Sartaj Bal 1J]

In addition to the response above, most reactions are already provided in their standard state. When all reactants and products are in their standard state, the reaction enthalpy is called standard reaction enthalpy.