Which of the following molecules has the lowest boiling point?
Question 7 options:
a) HCl
b) PH3
c) H2S
d) CH4
e) H2O
d) CH4
To determine which molecule has the lowest boiling point among the options given, we can examine the intermolecular forces that hold the molecules together.
Boiling point depends on the strength of intermolecular forces. Generally, the stronger the intermolecular forces, the higher the boiling point.
Let's analyze each option:
a) HCl (hydrogen chloride) - This compound is a polar molecule that experiences dipole-dipole interactions. Since it has stronger intermolecular forces compared to nonpolar molecules, it will likely have a higher boiling point.
b) PH3 (phosphine) - Phosphine is also a polar molecule but with weaker dipole-dipole interactions compared to HCl. As a result, the boiling point of PH3 is expected to be lower than that of HCl.
c) H2S (hydrogen sulfide) - H2S exhibits similar polarity to PH3. It has weaker dipole-dipole interactions relative to HCl, and hence, its boiling point should be lower than that of HCl.
d) CH4 (methane) - Methane is a nonpolar molecule, so it only experiences weak dispersion forces. Since dispersion forces are generally weaker than dipole-dipole interactions, CH4 is expected to have a lower boiling point than the polar molecules HCl, PH3, and H2S.
e) H2O (water) - Water is a highly polar molecule with strong hydrogen bonding between its molecules. Hydrogen bonding is the strongest intermolecular force among the options listed. Consequently, H2O is expected to have the highest boiling point.
Comparing the options, CH4 (option d) is a nonpolar molecule that does not experience strong intermolecular forces like dipole-dipole interactions or hydrogen bonding. Hence, CH4 is likely to have the lowest boiling point among the five choices.
To determine which molecule has the lowest boiling point, we need to compare the intermolecular forces present in each molecule.
a) HCl: This molecule is a polar covalent compound with hydrogen bonding. The HCl molecule can form dipole-dipole interactions.
b) PH3: This molecule is a nonpolar covalent compound, so it only has weak London dispersion forces.
c) H2S: This molecule is a polar covalent compound with hydrogen bonding. The H2S molecule can form dipole-dipole interactions.
d) CH4: This molecule is a nonpolar covalent compound, so it only has weak London dispersion forces.
e) H2O: This molecule is a polar covalent compound with hydrogen bonding. The H2O molecule can form dipole-dipole interactions.
Based on the above analysis, we can conclude that HCl, H2S, and H2O have stronger intermolecular forces (dipole-dipole interactions or hydrogen bonding) compared to PH3 and CH4, which only have weak London dispersion forces.
Therefore, among the given options, the molecule with the lowest boiling point is PH3 (option b) because it has the weakest intermolecular forces.