High School

Consider the gas-phase dimerization reaction:

\[ 2A(g) \longrightarrow A_2(g) \]

At 298 K, the values of the standard enthalpies of formation (\(\Delta H_f^\circ\)) for \(A(g)\) and \(A_2(g)\) are 55.6 kJ/mol and 156.4 kJ/mol, respectively. What is the standard enthalpy change (\(\Delta H^\circ\)) for the reaction?

A. -55.6 kJ/mol
B. 100.8 kJ/mol
C. 55.6 kJ/mol
D. -100.8 kJ/mol

Answer :

Final answer:

The correct answer is option b. In this chemistry question, we calculate the standard enthalpy change for a gas-phase dimerization reaction. By applying the given standard enthalpies of formation, we find the correct answer to be 100.8 kJ/mol.

Explanation:

Standard enthalpy change (ΔHo) can be calculated using the standard enthalpies of formation of reactants and products. In this case, for the dimerization reaction 2A(g) → A2(g), the equation becomes ΔHo = 2ΔHof(A2) - 2ΔHof(A).

Substitute the given values (ΔHof(A) = 55.6 kJ/mol, ΔHof(A2) = 156.4 kJ/mol) into the formula to calculate that the standard enthalpy change is 100.8 kJ/mol, which corresponds to option b) in the question.

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