WAEC Chemistry 2023 Objective — Question 46

Question 46 of 50 from the West African Examinations Council (WAEC) Chemistry 2023 Objective paper, with the correct answer and a full explanation.

Arrange the following compounds in decreasing order of their boiling points: NH3, HF, SiH4, CH4

A. NH3, CH4, SiH4, HF
B. CH4, SiH4, NH3, HF
C. HF, NH3, SiH4, CH4Correct
D. CH4, SiH4, HF, NH3

Explanation

NH3 and HF have higher boiling points than SiH4 and CH4 because NH3 and HF exhibit hydrogen bonding. HF has the strongest hydrogen bonding of common substances, so its boiling point is higher than NH3's. SiH4 has a higher boiling point than CH4 because it is heavier. Decreasing order: HF > NH3 > SiH4 > CH4.

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