Lithium be cut with a knife. When cut, it possesses a silvery-white color that quickly changes to gray as it oxidizes to lithium oxide. While it has one of the lowest melting points among all metals (180 °C), it has the highest melting and boiling points of the alkali metals. Lithium has a very low density (0.534 g/cm), comparable with pine wood. It is the least dense of all elements that are solids at room temperature; the next lightest solid element (potassium, at 0.862 g/cm) is more than 60% denser. Furthermore, apart from helium and hydrogen, it is less dense than
Standard enthalpy of formation (usually 25 °C or 298.15 K). Standard states are as follows: For example, the standard enthalpy of formation of carbon dioxide would be the enthalpy of the following reaction under the above conditions: All elements are written in their standard states, and one mole of product is formed. This is true for all enthalpies of formation. The standard enthalpy of formation is measured in units of energy per amount of substance, usually stated in kilojoule per mole (kJ mol), but also in kilocalorie per mole, joule per mole or kilocalorie per gram (any combination of these units conforming to the