Hypothetical chemical compound heat of formation ... can be used to determine whether a hypothetical compound is stable." However, "a negative formation enthalpy does not automatically imply the existence of a hypothetical compound." The method predicts that NaCl is stable but NeCl is not. It predicted XePtF based on the stability of OPtF. Hypothetical chemical compound A hypothetical chemical compound is a chemical compound that has been conceived of, but is not known to have been synthesized, observed, or isolated (identified or shown to exist). Some hypothetical compounds cannot form at all. Others might turn out to be highly unstable, decomposing, isomerizing, polymerizing,
Chemical substance FeS. The resulting compound has all the properties of a chemical substance and is not a mixture. Iron(II) sulfide has its own distinct properties such as melting point and solubility, and the two elements cannot be separated using normal mechanical processes; a magnet will be unable to recover the iron, since there is no metallic iron present in the compound. While the term "chemical substance" is a precise technical term that is synonymous with "chemical" for chemists, the word "chemical" is used in general usage in the English speaking world to refer to both (pure) chemical substances and mixtures (often