21) Which is expected to have the highest surface tension at 25°?
22) The magnitude of the heats of vaporization, fusion and sublimation of a substance reflect the
A) density of the substance.
B) magnitudes of the boiling and melting points of the substance.
C) strength of the covalent bonds between atoms in each molecule of the substance.
D) strength of the intermolecular forces of the substance.
23) For a particular compound, which is expected to be the largest in general?
A) the heat required to raise the temperature of one mole of the gas 10.0°C
B) the heat required to raise the temperature of one mole of the liquid 10.0°C
C) the molar heat of fusion at the normal melting point
D) the molar heat of vaporization at the normal boiling point
24) Which of the following phase changes has a positive value for its entropy change?
A) boiling water
B) formation of raindrops from a cloud
C) making dry ice from gaseous CO2
D) making ice cubes from liquid water
25) For which of the following phase changes is the sign of ΔS negative?
A) boiling of water
B) formation of snow from water vapor in clouds
C) melting of ice cream
D) sublimation of I2
26) When a substance melts at its normal melting point, the sign of ?H is ________ and the sign of ?S of this phase change is ________.
A) + , –
B) – , +
C) + , +
D) – , –
27) Ethyl chloride, C2H5Cl, is used as a local anesthetic. It works by cooling tissue as it vaporizes. The heat of vaporization is 26.4 kJ/mol. How much heat could be removed by 10.0 g of ethyl chloride?
A) 4.09 kJ
B) 170 kJ
C) 264 kJ
D) 1700 kJ
28) Bromine is one of only two elements that is a liquid at room temperature. Bromine has a heat of vaporization of 30.91 kJ/mol and its boiling point is 59°C. What is the entropy of vaporization for bromine?
A) -301 J/(mol ? K)
B) -93.1 J/(mol ? K)
C) 10.7 J/(mol ? K)
D) 93.1 J/(mol ? K)
29) CFC-11 (trichlorofluoromethane, CCl3F) has been used for many years as the working fluid in refrigerators. Given its heat of vaporization is 26.88 kJ/mol and its entropy of vaporization is 90.51 J/(mol ? K), what is the boiling point of CFC-11?
30) How much heat is released when 75.0 g of steam at 100.0°C is cooled to ice at -15.0°C? The enthalpy of vaporization of water is 40.67 kJ/mol, the enthalpy of fusion for water is 6.01 kJ/mol, the molar heat capacity of liquid water is 75.4 J/(mol ? °C), and the molar heat capacity of ice is 36.4 J/(mol ? °C).
A) 54.8 kJ
B) 195 kJ
C) 228 kJ
D) 248 kJ