Neco Model Questions Vol1 2018 Chemistry Question 21

Practice objective / multiple choice question 21 from the 2018 Neco Model Questions Vol1 Chemistry examination.

Neco Model Questions Vol1 2018 Chemistry Objective / Multiple Choice Hard Difficulty
Question 21 NECO_MODEL_QUESTIONS_VOL1 • 2018 • CHEMISTRY • objective

Using the bond dissociation energies given below, calculate the enthalpy change (ΔH) for the reactions \(\mathrm{F_2 + H_2 \rightarrow 2HF}\) and \(\mathrm{Cl_2 + H_2 \rightarrow 2HCl}\). The bond energies are: H-F = 565 kJ·mol⁻¹, H-Cl = 432 kJ·mol⁻¹, F-F = 158 kJ·mol⁻¹, Cl-Cl = 243 kJ·mol⁻¹, H-H = 436 kJ·mol⁻¹. Which reaction is more exothermic and, based on the data, why is HF a stronger acid than HCl in aqueous solution?

Answer Options

A. ΔH(F₂+H₂→2HF) = -536 kJ·mol⁻¹; ΔH(Cl₂+H₂→2HCl) = -185 kJ·mol⁻¹. Both reactions have equal exothermicity, and HF is a stronger acid due to its higher electronegativity alone.
Correct Answer B. ΔH(F₂+H₂→2HF) = -536 kJ·mol⁻¹; ΔH(Cl₂+H₂→2HCl) = -185 kJ·mol⁻¹. The fluorine reaction is more exothermic, and HF is a stronger acid because the H-F bond is highly polar and the small F⁻ ion is strongly stabilised in water.
C. ΔH(F₂+H₂→2HF) = -450 kJ·mol⁻¹; ΔH(Cl₂+H₂→2HCl) = -200 kJ·mol⁻¹. The chlorine reaction is more exothermic, and HCl is a stronger acid because the H-Cl bond is less polar and the larger Cl⁻ ion is better stabilized in water.
D. ΔH(F₂+H₂→2HF) = -600 kJ·mol⁻¹; ΔH(Cl₂+H₂→2HCl) = -150 kJ·mol⁻¹. The fluorine reaction is more exothermic, and HF is a stronger acid because the H-F bond is weaker than H-Cl.
Correct Answer
B
Correct Option:
ΔH(F₂+H₂→2HF) = -536 kJ·mol⁻¹; ΔH(Cl₂+H₂→2HCl) = -185 kJ·mol⁻¹. The fluorine reaction is more exothermic, and HF is a stronger acid because the H-F bond is highly polar and the small F⁻ ion is strongly stabilised in water.

About This Question

This is Neco Model Questions Vol1 2018 Chemistry Question 21. It is one of the objective questions from the 2018 Neco Model Questions Vol1 Chemistry examination.

Difficulty level: Hard .

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