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CAIE A-Level Chemistry A2 27.1.1 Trends the Trend in the Thermal Stability Questions

Practise explaining Group 2 thermal stability trends using ionic radius and charge density.

Syllabus
2028–2030
Course
Chemistry 9701
Level
A2

Exam points

  • explain Group 2 thermal stability trends from ionic radius and polarisation
  • link decomposition temperature to carbonate and nitrate stability

CAIE A-Level Chemistry A2 27.1.1 Trends the Trend in the Thermal Stability Questions question 1

[Maximum number: 2]

Potassium iodide, KI, is used as a reagent in both inorganic and organic chemistry.

KI slowly oxidises in air, forming I2\mathrm{I}_{2}.

reaction 14KI(s)+2CO2( g)+O2( g)→2 K2CO3( s)+2I2( s)ΔH⊖=−203.4 kJ mol−11 \quad 4 \mathrm{KI}(\mathrm{s})+2 \mathrm{CO}_{2}(\mathrm{~g})+\mathrm{O}_{2}(\mathrm{~g}) \rightarrow 2 \mathrm{~K}_{2} \mathrm{CO}_{3}(\mathrm{~s})+2 \mathrm{I}_{2}(\mathrm{~s}) \quad \Delta H^{\ominus}=-203.4 \mathrm{~kJ} \mathrm{~mol}^{-1}

Table 1.2 shows some data relevant to this question.

Table 1.2

Table 1.2

The Group 1 carbonates are much more thermally stable than the Group 2 carbonates. State and explain the trend in the thermal stability of the Group 2 carbonates.

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