States of Matter

States of Matter

Question

The formation of the oxide ion O2-(g) requires first an exothermic and then an endothermic step as shown below
straight O space left parenthesis straight g right parenthesis space space plus straight e to the power of minus space straight O to the power of minus left parenthesis straight g right parenthesis space increment straight H to the power of straight o space equals space minus space 142 space kJ space mol to the power of negative 1 end exponent
straight O to the power of minus space left parenthesis straight g right parenthesis space space plus straight e to the power of minus straight O to the power of 2 minus end exponent space left parenthesis straight g right parenthesis increment straight H to the power of straight o space equals space 844 space kJ space mol to the power of minus space

  • Oxygen is more electronegative

  • O- ion has comparatively larger size than oxygen atom

  • O- ion will tend to resist the addition of another electron

  • Oxygen has high electron affinity

Answer

C.

O- ion will tend to resist the addition of another electron

straight O to the power of minus space left parenthesis straight g right parenthesis space plus space straight e to the power of minus space rightwards arrow with space space on top space straight O to the power of 2 minus end exponent space left parenthesis straight g right parenthesis space increment straight H to the power of straight o space minus space 844 space kJ space mol to the power of negative 1 end exponent
This process is unfavourable in the gas phase because the resulting increase in electron-electron repulsion overweights the stability gained by achieving the noble gas configuration.

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