And it's given this value where the small zero here called not is basically represents standard state or a 1 bar. Okay? And this f is formation. So change in enthalpy, okay? So standard enthalpy of formation and it basically means it's the change in enthalpy for a reaction that creates 1 mol of compound from its constituent elements. For example, let's take the creation or formation of water from its constituents, from hydrogen and from oxygen, okay?