Question

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)

Answer 1

Answer:

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$_{g}$