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Ch.12 - Liquids, Solids & Intermolecular Forces

Chapter 12, Problem 90

Explain the observed trend in the boiling points of these compounds.

H2Te -2 °C

H2Se -41.5 °C

H2S -60.7 °C

H2O 100 °C

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Hey everyone were asked which statement describes the reason ammonia deviates from the trend of boiling points. Looking at our compounds. We see we have ammonia and we see that our three other compounds are all polar and because they are all polar, this means that they have dipole, dipole and London dispersion forces. Looking at our ammonia, we know that ammonia is capable of hydrogen bonding due to that nitrogen and we know that as our Mueller mass increases, our dispersion forces will also increase, which will subsequently increase our boiling points. But since ammonia is able to hydrogen bond this will offset its low molar mass, which gives it a higher boiling point than some of our heavier compounds. So our answer here is going to be c since ammonia is capable of hydrogen bonding and this is why it deviates from the trend of boiling points. So I hope that made sense. And let us know if you have any questions.