The generic structural formula for a 1-alkyl-3-methylimid- azolium cation is where R is a -CH2(CH2)nCH3 alkyl group. The melting points of the salts that form between 1-alkyl-3-methylimidazolium cation and the PF6- anion are as follows: R = CH2CH3 (m.p. = 60 °C), R = CH2CH2CH3 (m.p. = 40 °C), r = CH2CH2CH2CH3 (m.p. = 10 °C), and R = CH2CH2CH2CH2CH2CH3 (m.p. = -61 °C). Why does the melting point decrease as the length of alkyl group increases?

(b) What is the relationship between viscosity and temperature?

Based on their composition and structure, list CH₂Cl₂, CH₃CH₂CH₃, and CH₃CH₂OH in order of (a) increasing intermolecular forces (c) increasing surface tension

Liquids can interact with flat surfaces just as they can with capillary tubes; the cohesive forces within the liquid can be stronger or weaker than the adhesive forces between liquid and surface:

(b) Which of these diagrams, i or ii, rep- resents what happens when water is on a nonpolar surface?

The boiling points, surface tensions, and viscosities of water and several alcohols are listed in the following table:

b. How do you explain the fact that propanol and ethylene glycol have similar molecular weights (60 vs. 62 amu), yet the viscosity of ethylene glycol is more than 10 times larger than propanol?

Name the phase transition in each of the following situations and indicate whether it is exothermic or endothermic: (c) Rubbing alcohol in an open container slowly disappears.

Name the phase transition in each of the following situations and indicate whether it is exothermic or endothermic: (d) Molten lava from a volcano turns into solid rock.

Ethyl chloride (C₂H₅Cl) boils at 12 °C. When liquid C₂H₅Cl under pressure is sprayed on a room-temperature (25 °C) surface in air, the surface is cooled considerably. (a) What does this observation tell us about the specific heat of C₂H₅Cl(g) as compared with that of C₂H₅Cl(l)?

Ethyl chloride (C₂H₅Cl) boils at 12 °C. When liquid C₂H₅Cl under pressure is sprayed on a room-temperature (25 °C) surface in air, the surface is cooled considerably. (b) Assume that the heat lost by the surface is gained by ethyl chloride. What enthalpies must you consider if you were to calculate the final temperature of the surface?

For many years drinking water has been cooled in hot climates by evaporating it from the surfaces of canvas bags or porous clay pots. How many grams of water can be cooled from 35 to 20 °C by the evaporation of 60 g of water? (The heat of vaporization of water in this temperature range is 2.4 kJ/g. The specific heat of water is 4.18 J/g-K).

The critical temperatures and pressures of a series of halogenated methanes are as follows:

(a) List the intermolecular forces that occur for each compound.

The critical temperatures and pressures of a series of halogenated methanes are as follows: (c) Predict the critical temperature and pressure for CCl4 based on the trends in this table. Look up the experimentally determined critical temperatures and pressures for CCl4, using a source such as the CRC Handbook of Chemistry and Physics, and suggest a reason for any discrepancies.

(a) Place the following substances in order of increasing volatility: CH₄, CBr₄, CH₂Cl₂, CH₃Cl, CHBr₃, and CH₂Br₂. (b) How do the boiling points vary through this series? (c) Explain your answer to part (b) in terms of intermolecular forces.

(a) Two pans of water are on different burners of a stove. One pan of water is boiling vigorously, while the other is boiling gently. What can be said about the temperature of the water in the two pans?

You are high up in the mountains and boil water to make some tea. However, when you drink your tea, it is not as hot as it should be. You try again and again, but the water is just not hot enough to make a hot cup of tea. Which is the best explanation for this result? (a) High in the mountains, it is probably very dry, and so the water is rapidly evaporating from your cup and cooling it. (b) High in the mountains, it is probably very windy, and so the water is rapidly evaporating from your cup and cooling it. (c) High in the mountains, the air pressure is significantly less than 1 atm, so the boiling point of water is much lower than at sea level. (d) High in the mountains, the air pressure is significantly less than 1 atm, so the boiling point of water is much higher than at sea level.

Using the vapor-pressure curves in Figure 11.24, (d) estimate the external pressure at which diethyl ether will boil at 40 °C.

Appendix B lists the vapor pressure of water at various external pressures. (c) A city at an altitude of 5000 ft above sea level has a barometric pressure of 633 torr. To what temperature would you have to heat water to boil it in this city?

Referring to Figure 11.29, describe the phase changes (and the temperatures at which they occur) when CO2 is heated from -80 to -20°C at (a) a constant pressure of 3 atm,

The phase diagram for neon is

Use the phase diagram to answer the following questions. (a) What is the approximate value of the normal melting point?

Use the phase diagram of neon to answer the following questions. (a) What is the approximate value of the normal boiling point?

Use the phase diagram of neon to answer the following questions. (b) What can you say about the strength of the intermolecular forces in neon and argon based on the critical points of Ne and Ar (see Table 11.5.)?

At 25°C gallium is a solid with a density of 5.91 g/cm³ and a melting point, 29.8°C, just slightly above room temperature. The density of liquid gallium just above the melting point is 6.1 g/cm³. Based on this information, what unusual feature would you expect to find in the phase diagram of gallium?