AP Chem 3.1 and 3.2 Questions

The molecular formula and molar mass of two straight-chain hydrocarbons are listed in the table above. Based on the information in the table, which compound has the higher boiling point, and why is that compound's boiling point higher?

4H10 , because it has more electrons, resulting in greater polarizability and stronger dispersion forces

Which of the following is a list of the compounds in order of increasing boiling points?

Butane < acetone < 1-propanol

Based on the data in the table above, which of the following liquid substances has the weakest intermolecular forces?

CH3OH(l)

Which of the following lists the substances F2, HCl, and HF in order of increasing boiling point?

F2 < HCl < HF

The liquefied hydrogen halides have the normal boiling points given above. The relatively high boiling point of HF can be correctly explained by which of the following?

HF molecules tend to form hydrogen bonds.

Which statement best helps to explain the observation that NH3(l) boils at −28°C, whereas PH3(l) boils at −126°C?

NH3NH3 has hydrogen bonding that is stronger than the dipole-dipole forces in PH3PH3.

Based on the information in the table above, which of the compounds has the highest boiling point, and why?

Propanoic acid, because it can form intermolecular hydrogen bonds

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?

The London (dispersion) forces increase

Which of the following best helps to explain why CCl4 is a liquid whereas CI4 is a solid when both are at 25°C?

The London dispersion forces are stronger in CI4 than in CCl4 because CI4 has a more polarizable electron cloud than CCl4

The structural formulas for two isomers of 1,2-dichloroethene are shown above. Which of the two liquids has the higher equilibrium vapor pressure at 20°C, and why?

The trans-isomer, because it has only London dispersion forces, whereas the cis-isomer also has dipole-dipole interactions

At 298 K and 1 atm, bromine is a liquid with a high vapor pressure, whereas chlorine is a gas. This provides evidence that, under these conditions, the

forces among Br2 molecules are greater than those among Cl2 molecules

The figure above shows two closed containers. Each contains the same volume of acetone in equilibrium with its vapor at the same temperature. The vapor pressure of the acetone is

the same in both containers because the temperature is the same

On the basis of strength of intermolecular forces, which of the following elements would be expected to have the highest melting point?

Br2

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?

CS2(l), because it has weaker London dispersion forces

Which compound, chloroacetic acid or iodoacetic acid, most likely has the lower boiling point, and why?

Chloroacetic acid, because the London dispersion forces among its molecules are weaker.

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?

Compound 2, because it forms hydrogen bonds, whereas compound 1 does not

Ne, HF, C2H6, CH4 Which of the substances listed above has the highest boiling point, and why?

HF, because its molecules form hydrogen bonds

The diagram above shows molecules of Br2 and I2 drawn to the same scale. Which of the following is the best explanation for the difference in the boiling points of liquid Br2 and I2, which are 59oC and 184oC, respectively?

I2 molecules have electron clouds that are more polarizable than those of Br2 molecules, thus London dispersion forces are stronger in liquid I2.

Compared to the equilibrium vapor pressure of CH3OH(l) at 300 K, the equilibrium vapor pressure of C2H5OH(l) at 300 K is

lower, because London dispersion forces among C2H5OH molecules are greater than those among CH3OH molecules