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 never negative

Answer

C

Explanation

Heat of formation of compound may be positive or negative, e.g.,
`C(s)+O_(2)(g)rarrCO_(2)(g)" "DeltaH^(0)=-393.5kJmol^(-1)`
`N_(2)(g)+(1)/(2)O_(2)(g)rarrN_(2)O(g),DeltaH^(0)=+292kJmol^(-1)`