The enthalpies of elements in their standard states are taken as zero. The enthalpy of formation of a compound is-
1.
Generally negative
2.
Always positive
3.
Zero
4.
Never negative
Hint: In the formation reaction energy always release.
Step 1:
The standard enthalpy change for the formation of one mole of a compound from its elements in their most stable states of aggregation (also known as reference states) is called Standard Molar Enthalpy of Formation.
Step 2:
The enthalpy of formation is always negative because when the compound is formed from its elements in their most stable states of aggregation then energy always releases. It is an exothermic reaction
Hence, enthalpy of formation is genrally negative.
