Return to Matter Menu. All chemical substances are either solid, liquid or gas. To make comparisons easier, the chemistry community has agreed on a concept called "the standard state." The standard state of a chemical substance is its phase (solid, liquid, gas) at 25.0 °C and one atmosphere pressure.
Furthermore, what is heat of formation in chemistry?
The standard heat of formation is defined as the amount of heat absorbed or evolved at 25° C (77° F ) and at one atmosphere pressure when one mole of a compound is formed from its constituent elements, each substance being in its normal physical state (gas,…
Why is the standard enthalpy of formation of oxygen zero?
This is true for all enthalpies of formation. All elements in their standard states (oxygen gas, solid carbon in the form of graphite, etc.) have a standard enthalpy of formation of zero, as there is no change involved in their formation.