Final answer:
The correct relationship between the chemical species and the enthalpy change is represented in option (D), where the enthalpy change is +48 kJ for the reverse reaction with halved coefficients.
Step-by-step explanation:
When analyzing thermochemical equations, we must ensure that the enthalpy change (ΔH) listed corresponds to the stoichiometry of the provided reaction. The initial thermochemical equation given is:
3H2(g) + N2(g) → 2NH3(g), ΔH = −96 kJ
To find the correct relationship among the chemical species and the enthalpy change, we can manipulate the coefficients of the original equation, keeping in mind that the ΔH must be adjusted proportionally. Here are the steps to determine the correct answer:
- Halving the coefficients of the reactants and products would mean halving the enthalpy, hence option (A) is incorrect because it retains the original ΔH while decreasing the reaction scale.
- Option (B) has halved coefficients but lists ΔH as positive, which is incorrect since the sign of ΔH should remain negative when scale is simply reduced.
- Option (C) has the same coefficients as the original reaction but lists ΔH as positive, which is incorrect since reversing the reaction would not apply to an equation with the same direction.
- The correct answer is option (D) NH3(g) → 3/2 H2(g) + 1/2 N2(g), ΔH = +48 kJ. This is because the reaction is the reverse of the original, so the sign of ΔH is reversed, and because the coefficients are halved, the magnitude of ΔH is also halved.