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)

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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N₂  + O₂   →  2NO

Explanation:

  The given equations are:

      Mg + C + O   →     MgCO₃

      C +  O₂    →   CO

      N₂  + O₂   →  2NO

      N₂  + 2O₂    →  N₂O

      H₂ + O    →    HO

From the given equations only N₂  + O₂   →  2NO does not correspond to an expression of the standard molar enthalpy of formation.

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

It could have been properly written as

   N₂  +  O₂   →  NO

your answer is c) plasma

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