5. For which of the following reactions would the heat of reaction be labelled ∆Hf°? a) PCl3 + ½ O2(g) ->POCl3(g) b) CaO(s) + SO2(g) -> CaSO3(s) c) Al(s) + 3/2O2(g) + 3/2H2(g) -> Al(OH)3(s) d) ½ N2O(g) + 1/4 O2(g) -> NO(g)

The reaction Al(s) + 3/2O2(g) + 3/2H2(g) -> Al(OH)3(s) can be labeled as  standard enthalpy of formation  (∆Hf°).

In chemistry, the standard enthalpy of formation refers to the heat evolved or absorbed when a substance is formed from its constituent elements under standard conditions.

As such, we can see that the compound Al(OH)3(s) in option C was formed from its components; aluminium, oxygen and hydrogen therefore, the reaction Al(s) + 3/2O2(g) + 3/2H2(g) -> Al(OH)3(s) can be labeled as  standard enthalpy of formation  (∆Hf°).

Learn more about standard enthalpy of formation : link

C

Explanation:

∆H°f means the enthalpy change of formation of one mole of substance by its constituent elements under standard conditions.

So in an equation for ∆H°f, we must see 2 or more elements as reactants combining to form a compound.

In the 4 answers, only C represents elements forming a substance (Al(s) + 3/2O2(g) + 3/2H2(g) -> Al(OH)3(s)),

while the others include compounds as one of their reactants.

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explanation:

chemical digestion occurs in the stomach were hcl and pepsin forms chyme, the mouth in which salivary amylase breaks down starch to form bolus, and the small intestine specifically the duodenum.