Which of the following has a boiling point which does not fit the general trend.
NH3
PH3
SbH3
AsH3
I am going with NH3 as i think its to do with "the larger the compound the greater the boiling point"(Vander waals forces)
Am I correct?
NH3 does not fit the general trend due to the greater number of inter-molecular forces required to release molecules from the liquid to gaseous state. Due to the N and H, the NH3 molecule exhibits hydrogen bonding, which is much stronger than the dipole-dipole forces between the rest of the molecules.
Yes, you are correct in thinking that the boiling point generally increases with increasing molecular size due to the strength of intermolecular forces, specifically van der Waals forces. However, to determine which compound's boiling point does not fit the general trend, we need to compare the trends in boiling points for each compound.
The general trend for boiling points in this case is that the boiling point increases as we move down a group in the periodic table. This is because the size of the atom or molecule increases down a group, causing an increase in London dispersion forces (a type of van der Waals force) between the molecules.
Let's compare the boiling points of the given compounds:
- NH3 (ammonia) has a boiling point of -33.34°C.
- PH3 (phosphine) has a boiling point of -87.7°C.
- SbH3 (antimony trihydride) has a boiling point of -17.2°C.
- AsH3 (arsine) has a boiling point of -62.5°C.
From these boiling points, we can see that the trend generally follows the pattern of increasing boiling points as we move down the group. However, the boiling point of SbH3 (-17.2°C) seems to deviate from the trend. It is lower than the boiling point of AsH3, which should be higher based on the general trend.
Therefore, SbH3 is the compound whose boiling point does not fit the general trend.
Yes, you are correct. Among the options given, NH3 (ammonia) has a deviation from the general trend in boiling points. The general trend is that, as the molecular weight increases, the boiling point also tends to increase due to stronger van der Waals forces.
However, NH3 has a lower boiling point compared to PH3 (phosphine), SbH3 (stibine), and AsH3 (arsine), despite having a higher molecular weight. This is because NH3 can form hydrogen bonds, which are stronger than van der Waals forces. Hydrogen bonding contributes to the higher boiling point of NH3 compared to the other compounds, even though its molecular weight is lower.