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Question:

Choose the reaction(s) from the following options, for which the standard enthalpy of reaction is equal to the standard enthalpy of formation.

18S8(s)+O2(g)→SO2(g)

32O2(g)→O3(g)

2H2(g)+O2(g)→2H2O(l

2C(g)+3H2(g)→C2H6(g

Solution:

Correct option is C. 32O2(g)→O3(g)
Standard enthalpy of formation: The standard enthalpy of formation of a compound is the change in the standard enthalpy when one mole of the compound is formed starting from the requisite amounts of elements in their stable standard state.