Which thermochemical equation gives the value of the standardenthalpy of formati

Question

Which thermochemical equation gives the value of the standardenthalpy of formation for NH4ClO4 (s)?
(Please note: the molecular formula contain subscripts, e.g. 2 H2(g) refers to two moles of molecular hydrogen gas).

a. N (g) + 4 H (g) + Cl (g) + 4 O(g) --> NH4ClO4 (s)
b. N (g) + 2 H2 (g) + Cl2(l) + 2 O2 (g) --> NH4ClO4 (s)
c. N2 (g) + 4 H2 (g) + Cl2(l) + 4 O2 (g) --> 2 NH4ClO4 (s)
d. N2 (g) + H2 (g) + Cl2(g) + O2 (g) --> NH4ClO4 (s)
e. ½ N2 (g) + 2 H2(g) + ½ Cl2 (g) + 2 O2 (g) --> NH4ClO4 (s)

Explanation / Answer

The equation for standard enthalpy of formation means theproduction of 1 NH4ClO4 from its elements. Eliminate A and B because Nitrogen is N2(g) notN(g) Eliminate C because standard enthalpy of formation means1NH4ClO4 Eliminate D because the left and the right side is notbalanced. Only choice E shows the formation of 1 NH4ClO4 from the elements inthe formula and is also balanced.

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