The enthalpy of elements in their standard atates are taken as zero .The enthalpy of formation of a compound:

Options

A. is always negative
B. is always positive
C. may be positive or negative
D. is negative negative

Answer

C

Explanation

Combustion of elements to form a compound can be exothermic endothermic e.g.,
`C + O_(2) rarr CO_(2)` is exothermic
whereas, `C + 2S rarr CS_(2)` is endothermic
Hence, enthalpy of formation can be positive or negative.