Respuesta :
Answer: The correct answer is Option A.
Explanation:
Standard enthalpy of formation is the change in enthalpy of one mole of a substance present at the standard state that is 1 atm of pressure and 298 K of temperature. The substance is formed from its pure elements under the same conditions.
We are given a chemical compound having chemical formula [tex]Ca(NO_3)_2[/tex]
This compound is formed by the combination of calcium, nitrogen and oxygen elements.
The chemical equation for the formation of [tex]Ca(NO_3)_2[/tex] from the components in their standard states follows:
[tex]Ca+N_2+3O_2\rightarrow Ca(NO_3)_3[/tex]
Hence, the correct answer is Option A.
The standard enthalpy of formation for Ca(NO₃)₂ is illustrated by:
(A) Ca(s) + N₂(g) + 3 O₂ → Ca(NO₃)₂(s)
The standard enthalpy of formation (ΔH°f) is defined as the change in enthalpy when one mole of a substance in the standard state is formed from its pure elements under the same conditions. All the substances must be in their most stable form.
Let's consider which of the following reactions illustrates ΔH°f for Ca(NO₃)₂.
(A) Ca(s) + N₂(g) + 3 O₂ → Ca(NO₃)₂(s)
YES. It has all the elements of the definition of standard enthalpy of formation.
(B) Ca²⁺(aq) + 2 NO₃⁻(aq) → Ca(NO₃)₂(aq)
NO. NO₃⁻ is not a pure element but a polyatomic ion.
(C) Ca(s) + 2 N(g) + 6 O(g) → Ca(NO3₃)₂ (s)
NO. The most stable form of nitrogen and oxygen is as diatomic molecules.
(D) Ca(NO₃)₂(aq) → Ca²⁺(aq) + 2 NO₃⁻(aq)
NO. This is not a formation reaction but a dissociation one.
(E) Ca(NO₃)₂(s) → Ca(s) + N₂(g) + 3 O₂(g)
NO. This is not a formation reaction but a decomposition one.
The standard enthalpy of formation for Ca(NO₃)₂ is illustrated by:
(A) Ca(s) + N₂(g) + 3 O₂ → Ca(NO₃)₂(s)
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