Since, the enthalpy of the elements in their standard states is taken to be zero, the heat of formation $(Δ H_{f})$ of compounds:

is always negative

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is always positive

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is zero

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may be positive or negative

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Solution

The correct option is C may be positive or negative
Enthalpy of elements in their standard states is taken to be zero, but the heat of formation of compounds depends on the enthalpy of compounds formed at standard states which can be both negative as well as positive.
Their is no restriction over enthalpy of compounds formed at standard state.
Hence, the value of heat of formation can also of any positive or negative value.
Hence, answer is option $D$ .

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Similar questions

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

Since the enthalpy of elements in their natural state is taken to be zero, the heat of formation

(Δ_{f} H)

of compounds is zero.

Q. The enthalpies of elements are always taken to be zero.

The enthalpies of all elements in their standard state at

25^{\circ} C

are taken to be zero.

I

. The enthalpy of formation (

Δ H_{f}

) of

{B r}_{2} (g)

1.00 a t m

and

298 K

0 k J / m o l

I I

. The

Δ H_{f}

0

for elements in their standard state.

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Since, the enthalpy of the elements in their standard states is taken to be zero, the heat of formation (ΔHf) of compounds:

Since, the enthalpy of the elements in their standard states is taken to be zero, the heat of formation $(Δ H_{f})$ of compounds: