Which of the following equations represents a formation reaction?a)b)c)d)Correct answer is option 'B'. Can you explain this answer?

Question

Answer

The standard enthalpy of formation of a compound is defined as the heat associated with the formation of one mole of the compound from its elements in their standard states. Most formation reactions are exothermic, but some are endothermic.

Carbon monoxide (CO) is not an element, in its reaction with oxygen gas, so the reaction is not a formation reaction.

In the reaction with hydrogen and bromine gases reacting, bromine is not in its standard state, which is liquid not gas. Bromine and mercury are the only two elements that are liquid in its standard state. The formation reaction of HBr would look like this:

H₂ (g) + Br₂ (1) + 2BHr (g)

In the reaction with hydrogen and oxygen gases reacting, water on the product state is not in its standard state. The formation reaction of H₂O would look like this:

In the reaction with rhombic sulfur and chlorine gas, there are elements in their standard state on the reactant side and only one product in its standard state. Sulfur is peculiar in that sulfur is not monoatomic and additionally has two forms, rhombic and monoclinic, and rhombic is the more stable form. The formation reaction of is SC1₂ correct as stated.

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