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Problem 54
Which evaporates more quickly: 55 mL of water (H2O) in a beaker or 100 mL of acetone [(CH3)2CO] in an identical beaker under identical conditions? Is the vapor pressure of the two substances different? Explain.
- Why does spilling room-temperature water over your skin on a hot day cool you down while spilling room-temperature vegetable oil does not?
Problem 55
- Why is the heat of vaporization of water greater at room temperature than at its boiling point?
Problem 56
- The human body obtains 915 kJ of energy from a candy bar. If this energy were used to vaporize water at 100.0 °C, how much water (in liters) could be vaporized? (Assume the density of water is 1.00 g/mL.)
Problem 57
- A 100.0-mL sample of water is heated to its boiling point. How much heat (in kJ) is required to vaporize it? (Assume a density of 1.00 g/mL.)
Problem 58
Problem 59
Suppose that 0.95 g of water condenses on a 75.0-g block of iron that is initially at 22 °C. If the heat released during condensation goes only to warming the iron block, what is the final temperature (in °C) of the iron block? (Assume a constant enthalpy of vaporization for water of 44.0 kJ/mol.)
Problem 61
This table displays the vapor pressure of ammonia at several different temperatures. Use the data to determine the heat of vaporization and normal boiling point of ammonia.
Temperature (K) Pressure (torr)
200 65.3
210 134.3
220 255.7
230 456.0
235 597.0
- This table displays the vapor pressure of nitrogen at several different temperatures. Use the data to determine the heat of vaporization and the normal boiling point of nitrogen. Temperature (K) Pressure (torr) 65 130.5 70 289.5 75 570.8 80 1028 85 1718
Problem 62
Problem 63
Ethanol has a heat of vaporization of 38.56 kJ/mol and a normal boiling point of 78.4 °C. What is the vapor pressure of ethanol at 15 °C?
Problem 64
Benzene has a heat of vaporization of 30.72 kJ/mol and a normal boiling point of 80.1 °C. At what temperature does benzene boil when the external pressure is 445 torr?
Problem 65
Carbon disulfide has a vapor pressure of 363 torr at 25 °C and a normal boiling point of 46.3 °C. Find ΔHvap for carbon disulfide.
- Methylamine has a vapor pressure of 344 torr at -25 °C and a boiling point of -6.4 °C. What is the ΔHvap for methylamine?
Problem 66
Problem 67
How much energy is released when 65.8 g of water freezes?
Problem 68
Calculate the amount of heat required to completely sublime 50.0 g of solid dry ice (CO2) at its sublimation temperature. The heat of sublimation for carbon dioxide is 32.3 kJ/mol.
Problem 69
An 8.5-g ice cube is placed into 255 g of water. Calculate the temperature change in the water upon the complete melting of the ice. Assume that all of the energy required to melt the ice comes from the water.
Problem 70
How much ice (in grams) would have to melt to lower the temperature of 352 mL of water from 25 °C to 5 °C? (Assume the density of water is 1.0 g/mL.)
- How much heat (in kJ) is required to warm 10.0 g of ice, initially at -10.0 °C, to steam at 110.0 °C? The heat capacity of ice is 2.09 J/g°C, and that of steam is 2.01 J/g°C.
Problem 71
- How much heat (in kJ) is evolved in converting 1.00 mol of steam at 145 °C to ice at -50 °C? The heat capacity of steam is 2.01 J/g°C, and that of ice is 2.09 J/g°C.
Problem 72
Problem 73
Consider the phase diagram shown here. Identify the states present at points a through g.
- Consider the phase diagram for iodine shown here. a. What is the normal boiling point for iodine? b. What is the melting point for iodine at 1 atm? c. What state is present at room temperature and normal atmospheric pressure? d. What state is present at 186 °C and 1.0 atm?
Problem 74
Problem 75
Nitrogen has a normal boiling point of 77.3 K and a melting point (at 1 atm) of 63.1 K. Its critical temperature is 126.2 K and its critical pressure is 2.55×104 torr. It has a triple point at 63.1 K and 94.0 torr. Sketch the phase diagram for nitrogen. Does nitrogen have a stable liquid state at 1 atm?
Problem 76
Argon has a normal boiling point of 87.2 K and a melting point (at 1 atm) of 84.1 K. Its critical temperature is 150.8 K and its critical pressure is 48.3 atm. It has a triple point at 83.7 K and 0.68 atm. Sketch the phase diagram for argon. Which has the greater density, solid argon or liquid argon?
Problem 77a
The phase diagram for sulfur is shown here. The rhombic and monoclinic states are two solid states with different structures. a. Below what pressure does solid sulfur sublime?
Problem 77b
The phase diagram for sulfur is shown here. The rhombic and monoclinic states are two solid states with different structures. b. Which of the two solid states of sulfur is more dense?
- Water has a high boiling point given its relatively low molar mass. Why?
Problem 79
Problem 80
Water is a good solvent for many substances. What is the molecular basis for this property, and why is it significant?
- Explain the role of water in moderating Earth's climate.
Problem 81
- How is the density of solid water compared to that of liquid water atypical among substances, and why is this significant?
Problem 82
Problem 83
Explain the observed trend in the melting points of the hydrogen halides.
HI -50.8 °C
HBr -88.5 °C
HCl -114.8 °C
HF -83.1 °C
Problem 84
Explain the observed trend in the boiling points of these compounds.
H2Te -2 °C
H2Se -41.5 °C
H2S -60.7 °C
H2O 100 °C