Topics: Intermolecular forces, heating curves, phase diagrams, Clausius-Clapyron
ID: 862875 • Letter: T
Question
Topics: Intermolecular forces, heating curves, phase diagrams, Clausius-Clapyron equation, and Unit cell calculations
1. If 42.0 kJ of heat is added to a 32.0 g sample of liquid methane under 1 atm of pressure at a temperature of -170 oC, what are the final state and temperature of the methane once the system equilibrates? Assume no heat is lost to the surroundings. The normal boiling point of methane is -161.5 oC. The specific heats of liquid and gaseous methane are 3.48 and 2.22 J/g-K, respectively.
2. The phase diagram for a hypothetical substance is shown below:
a) Estimate the normal boiling point and freezing point of the substance.
b) What is the physical state of the substance under the following conditions?
i) T = 150 K, P = 0.2 atm
ii) T = 100 K, P = 0.8 atm
iii) T = 300 K, P = 1.0 atm
c) What is the triple point of the substance?
3. Benzoic acid, C6H5COOH, melts at 122 oC. The density in the liquid state at 130 oC is 1.08 g/cm3. The density of solid benzoic acid at 15 oC is 1.266 g/cm3.
a) In which of these two states is the average distance between molecules greater?
b) Explain the difference in densities at the two temperatures in terms of the relative kinetic energies of the molecules.
4. At standard temperature and pressure the molar volume of Cl2 and NH3 gases are 22.06 L and 22.40 L, respectively.
a) Given the different molecular weights, dipole moments, and molecular shapes, why are their molar volumes nearly the same?
b) On cooling to 160 K, both substances form crystalline solids. Do you expect the molar volumes to decrease or increase on cooling to 160 K?
c) The densities of crystalline Cl2 and NH3 at 160 K are 2.02 and 0.84 g/cm3, respectively. Calculate their molar volumes.
d) Are the molar volumes in the solid state as similar as they are in the gaseous state? Explain.
e) Would you expect the molar volumes in the liquid state to be closer to those in the solid or gaseous state?
5. Draw a heating curve for the conversion of 100 g of ice at -25 oC to steam at 125 oC. Temperatures should be labled but the sketch does not have to be to scal and the values for q do not need to be identified.
a) Comparing the heating of water to the heating of steam, these lines should have a different slope. Explain why that is.
b) The length of the line for the conversion of water to steam should be much longer than the line representing the amount of heat required to convert ice to water. Explain why that is.
c) The specific heat capacities for ice, water, and steam are 2.03, 4.18, and 2.01 J/g-oC.
The DHvap of water is 40.65 kJ/mol and the DHfus of water is 6.01 kJ/mol. Calculate the amount of heat required to convert 100 g of ice at 0 oC to steam at 100 o.
6. The following quote about ammonia (NH3) is from a textbook of inorganic chemistry:
Explanation / Answer
2)
(a) Estimate the normal boiling point and freezing point of the substance.
"NORMAL" INDICATES BEHAVIOR AT 1 ATMOSPHERE OF PRESSURE.
FIRST AREA ON LEFT IS SOLID, THEN LIQUID, THEN GAS.
BOILING POINT: about 360 K (the liquid/gas transition @ 1 atm)
FREEZING POINT: about 260 K (the solid/liquid transition @ 1 atm)
(b) What is the physical state of the substance under the following conditions?
(i) T = 150 K, P = 0.2 atm GAS
(ii) T = 100 K, P = 0.8 atm SOLID
(iii) T = 300 K, P = 1.0 atm LIQUID
7)
Bromine Vapor turns into bromine liquid as it is cooled
Gas to liquid, exothermic
Crystals of iodine disappear from an evaporating dish as they stand in a fume hood
Solid to gas. (sublimation) endothermic.
Rubbing alcohol in an open container slowly disappears
liquid to vapor (evaporation). endothermic
Molten Lava from a volcano turns into solid rock
liquid to solid, exothermic
16)
A) Well, if it
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