What is a Standard State or Reference State of an element??? Can someone please give me a simple explanation of what a standard state or reference state is? I don't quite understand the way wiki describes it which is - The standard state, also known as reference state, of an element is defined as its thermodynamically most stable state at 1 bar at a given temperature (typically at 298.15 K). In thermochemistry, an element is defined to have an enthalpy of formation of zero in its standard state. For example, the reference state for carbon is graphite, because the structure of graphite is more stable than that of the other allotropes.