The enthalpies of elements in their standard states are taken as zero. 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

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Solution

(c)

Combustion of elements to form a compound can be exothermic or endothermic. e.g.,
$C + O_{2} \to C O_{2}$ is exothermic.
whereas, $C + 2 S \to C S_{2}$ is endothermic.
Hence, enthalpy of formation can be positive or negative.

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The enthalpies of elements in their standard states are taken as zero. 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

(c) Combustion of elements to form a compound can be exothermic or endothermic. e.g., C+O2→CO2 is exothermic. whereas, C+2S→CS2 is endothermic. Hence, enthalpy of formation can be positive or negative.

The enthalpies of elements in their standard states are taken as zero. 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

(c)

Combustion of elements to form a compound can be exothermic or endothermic. e.g.,
$C + O_{2} \to C O_{2}$ is exothermic.
whereas, $C + 2 S \to C S_{2}$ is endothermic.
Hence, enthalpy of formation can be positive or negative.