Chemistry, 14.10.2019 17:30 alexthebest3976

Which of the following chemical equations does not correspond to a standard molar enthalpy of formation? a. mg(s) + c(s) + 3/2 o_2(g) rightarrow mgco_3(s) b. c(s) + 1/2 o_2(g) rightarrow co(g) c. n_2(g) + o_2(g) rightarrow 2 no(g) d. n_2(g) + 2 o_2(g) rightarrow n_2o_4(g) e. h_2(g)+l/2 o_2(g) rightarrow h_2o(l)

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Answer from: diamondalize21p84czi

The chemical equation that does not correspond to a standard molar enthalpy of formation is c. N₂(g) + O₂(g) ⇒ 2 NO(g).

The standard molar 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 chemical equations correspond to a standard molar enthalpy of formation.

a. Mg(s) + C(s) + 3/2 O₂(g) ⇒ MgCO₃(s)

YES. It has all the elements of the definition of standard enthalpy of formation.

b. C(s) + 1/2 O₂(g) ⇒ CO(g)

YES. It has all the elements of the definition of standard enthalpy of formation.

c. N₂(g) + O₂(g) ⇒ 2 NO(g)

NO. 2 moles of NO are formed.

d. N₂(g) + 2 O₂(g) ⇒ N₂O₄(g)

YES. It has all the elements of the definition of standard enthalpy of formation.

e. H₂(g) + 1/2 O₂(g) ⇒ H₂O(l)

YES. It has all the elements of the definition of standard enthalpy of formation.

The chemical equation that does not correspond to a standard molar enthalpy of formation is c. N₂(g) + O₂(g) ⇒ 2 NO(g).

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Answer from: lolagrace06

N₂ $_{s}$ + O₂ $_{g}$ → 2NO $_{g}$

Explanation:

The given equations are:

Mg $_{s}$ + C $_{s}$ + $\frac{3}{2}$ O $_{g}$ → MgCO₃ $_{s}$

C $_{s}$ + $\frac{1}{2}$ O₂ $_{g}$ → CO $_{g}$

N₂ $_{s}$ + O₂ $_{g}$ → 2NO $_{g}$

N₂ $_{s}$ + 2O₂ $_{g}$ → N₂O $_{g}$

H₂ $_{g}$ + $\frac{1}{2}$ O $_{g}$ → HO $_{l}$

From the given equations only N₂ $_{s}$ + O₂ $_{g}$ → 2NO $_{g}$ does not correspond to an expression of the standard molar enthalpy of formation.

The heat of formation is the heat liberated or absorbed when one mole of a compound is formed from its constituent elements under standard conditions.

The equation must result in the formation of only one mole of the compound.

It could have been properly written as

$\frac{1}{2}$ N₂ $_{s}$ + $\frac{1}{2}$ O₂ $_{g}$ → NO $_{g}$

Answer from: Quest

The correct answer would be 1. precipitation

Answer from: Quest

"among the transition metal elements, manganese and zinc have a slight lowering of electronegativities. the reason behind this is that the nuclear charges of these elements are slightly weaker than the other transition metal elements due to the way their valence electrons are filled up. both manganese and zinc have their valence electrons filled up to the 4th shell with 1 pair of electrons (4s2) completely occupying it. although the electrons in the 3rd shell (3d) are yet to be paired since the outer most shell is filled up, the ability of the nucleus to attract electrons is lessened. hence, the electronegativity (or the ability to attract electrons) is lessened."

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