Question

1. if the pressure of each gas is increased at constant temperature until condensation occurs, which gas will condense at the lowest pressure? (a) methane (b) ethane (c) butane (d) all the gases will condense at the same pressure. 15. based on the information in the table above, which liquid, cs₂(l) or ccl₄(l), has the higher equilibrium vapor pressure at 25°c, and why? (a) cs₂(l), because it has stronger london dispersion forces (b) cs₂(l), because it has weaker london dispersion forces (c) ccl₄(l), because it has stronger london dispersion forces (d) ccl₄(l), because it has weaker london dispersion forces 16. the boiling points of the elements helium, neon, argon, krypton, and xenon increase in that order. which of the following statements accounts for this increase? (a) the london (dispersion) forces increase. (b) the hydrogen bonding increases. (c) the dipole-dipole forces increase. (d) the chemical reactivity increases. 17. based on the structures shown above, which of the following statements identifies the compound with the higher boiling point and provides the best explanation for the higher boiling point? (a) compound 1, because it has stronger dipole-dipole forces than compound 2 (b) compound 1, because it forms hydrogen bonds, whereas compound 2 does not (c) compound 2, because it is less polarizable and has weaker london dispersion forces than compound 1 (d) compound 2, because it forms hydrogen bonds, whereas compound 1 does not

Explanation:

• For question 14:
• The boiling point of a substance is related to the strength of its intermolecular forces. Larger molecules (with more electrons) have stronger London dispersion forces.
• Methane (\(CH_4\)) has the formula \(C_1H_4\), ethane (\(C_2H_6\)), and butane (\(C_4H_{10}\)).
• As the number of carbon atoms increases, the molar mass and the number of electrons increase.
• Butane has the largest molar mass among the three, so it has the strongest London dispersion forces.
• At a constant temperature, the gas with the strongest intermolecular forces (butane) will condense at the lowest pressure.
• For question 15:
• Vapor pressure is inversely related to the strength of intermolecular forces.
• \(CS_2\) has a lower boiling point (\(46.5^{\circ}C\)) compared to \(CCl_4\) (\(76.7^{\circ}C\)).
• A lower boiling point indicates weaker intermolecular forces.
• \(CS_2\) has weaker London dispersion forces (since it has a lower molar mass) than \(CCl_4\).
• Weaker intermolecular forces mean more molecules can escape into the vapor phase, resulting in a higher vapor pressure. So \(CS_2\) has a higher vapor pressure because it has weaker London dispersion forces.
• For question 16:
• Helium, neon, argon, krypton, and xenon are noble gases.
• Noble gases are non - polar, so they only have London dispersion forces.
• As we move from helium to xenon, the molar mass (and the number of electrons) increases.
• An increase in the number of electrons leads to an increase in the strength of London dispersion forces.
• Stronger London dispersion forces require more energy to overcome, so the boiling point increases.
• For question 17:
• Compound 2 (\(CH_3 - CH_2 - CH_2 - CH_2-\ddot{N}H_2\)) has \(N - H\) bonds.
• \(N - H\) bonds can participate in hydrogen bonding.
• Compound 1 (\(CH_3 - CH_2-\ddot{N}(CH_3)_2\)) does not have \(N - H\) bonds (the \(N\) is bonded to \(C\) atoms only), so it cannot form hydrogen bonds.
• Hydrogen bonding is a stronger intermolecular force than dipole - dipole forces (which both compounds have due to the polar \(N\) atom).
• Stronger intermolecular forces (hydrogen bonding in compound 2) lead to a higher boiling point.

Answer:

1. C. Butane
2. B. \(CS_2(l)\), because it has weaker London dispersion forces
3. A. The London (dispersion) forces increase
4. D. Compound 2, because it forms hydrogen bonds, whereas compound 1 does not