Chemistry · Enthalpies of bond dissociation, combustion, formation, atomization, sublimation, phase transition, hydration, ionization and solution
The standard enthalpies of elements in their standard(natural) states are taken
The standard enthalpies of elements in their standard(natural) states are taken as zero. On basis of this statement, we can say that the enthalpy of formation of a compound :
- A. Is always negative
- B. Is always positive
- C. May be positive or negative
- D. Is never negative
Step-by-step solution
The enthalpy of formation is defined as the enthalpy change when one mole of a compound is formed from its constituent elements in their standard states. Since the standard enthalpies of elements are zero, the enthalpy of formation reflects the stability of the compound relative to its elements. This value can be either negative (exothermic formation) or positive (endothermic formation) depending on the compound. For example, formation of H2O is exothermic (negative), while formation of NO is endothermic (positive). Therefore, it may be positive or negative.
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