Define and explain the standard enthalpy of formation `(Delta_(r)H^(theta))`.

Explanation

The heat change involved in the reaction of formation of one mole of a compound is called enthalpy of formation.
If all the substances are in the standard states the enthalpy of formation is called standard enthalpy of formation:
`Ex. (1) underset("graphite")(C)+2S_(g) to CS_(2(g)) triangleH=91.9KJ`
(2) `underset("Rhombic")(S+O_(2(g)) to SO_(2(g)) triangleH=-297.5KJ`