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CAIE A-Level Chemistry AS 11.2.3 Thermal Stabilities of the Hydrogen Halides Questions

Practise ranking hydrogen halide thermal stability and explaining the trend through H–X covalent bond strength.

Syllabus
2028–2030
Course
Chemistry 9701
Level
AS

Exam points

  • state that thermal stability decreases from HCl to HBr to HI down Group 17
  • link the trend to increasing halogen size, longer H–X bonds and decreasing bond strength
  • use bond-energy data to identify which hydrogen halide decomposes most readily on heating

CAIE A-Level Chemistry AS 11.2.3 Thermal Stabilities of the Hydrogen Halides Questions question 1

[Maximum number: 1]

The Group 17 elements are oxidising agents.

Cl2\mathrm{Cl}_{2} and Br2\mathrm{Br}_{2} can each react with NH3\mathrm{NH}_{3} to give N2\mathrm{N}_{2} and a hydrogen halide, HX .

3X2+2NH3→ N2+6HX3 \mathrm{X}_{2}+2 \mathrm{NH}_{3} \rightarrow \mathrm{~N}_{2}+6 \mathrm{HX}

X = Cl or Br

The relative bond strengths of X-X and H-X determine the difference in enthalpy change of the two reactions.

Describe the relative thermal stabilities of HCl and HBr .

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