PS 25 2022 key~

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Chemistry

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Jan 9, 2024

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Problem Set 25 – Phase Diagrams Chem 105 1. List and briefly define (1 sentence) all possible phase changes. Boiling- vaporization of the liquid which occurs at the boiling point which is the temperature at which the vapor pressure of the liquid is equal to the pressure exerted on the liquid by the surroundings Melting- transition from a solid to a liquid Sublimation - solid to gas 2. In the following phase diagram: (a) Which phases corresponds to regions I, II, and III? I = solid II = liquid III = gas (b) What is the significance of points a-d? a = normal melting point (T at which the solid melts at 1 atm) b = normal boiling point (T at which the liquid boils at 1 atm) c = critical point (T and P at which liquid and vapor become indistinguishable) d = triple point (T and P at which solid/liquid/gas all coexist) (c) What do each of the lines represent? line between I and III is solid-gas co-existence line (subliming) line between I and II is solid-liquid co-existence line (melting) line between II and III is the liquid-gas co-existence line (boiling) 3. (a) What phase exists at the crossing of the dashed lines on the phase diagram to the right? The substance is a solid at 25 0 C and 1 atm. (b) What happens if you change the P or T along the dashed lines in each direction? Increasing the temperature at a constant P would cause sublimation. Increasing the pressure at a constant T would not cause a phase change. 4. The image to the right is the phase diagram of an imaginary molecular compound X. a) Does the green line represent a series of (a) freezing points, (b) sublimation points, (c) boiling points, or (d) critical points? It’s the transition from solid to gas. It represents a series of sublimation points.

b) Does the solid form of compound X (Figure P6.3) float on the liquid as the liquid begins to freeze at P = 300 atm? Solid is favored at higher pressure, therefore its more dense. It won’t float on water. 5. More questions about compound X. a) If a sample of X is left outside in a sealed container on a hot summer day, will the X in the container be a solid, liquid, or a gas? A hot summer day is 1 atm and 30 o C. Its solid phase. b) Suppose you bring the sample of X inside and place it in an uncovered pot of boiling water on your kitchen stove. What phase changes, if any, will occur? On boiling the water temperature reached 100 o C and the pressure is 1 atm. It changes from solid to gas c) Another sample of X is stored in a pressurized container (P = 50 atm) in a freezer at 0°C. If the sample is then transferred to an oven and slowly warmed to 250°C, what phase changes, if any, will X undergo? The point for 50 atm and 0°C is the solid phase. The point for 50 atm and 250°C is in the gas phase. The compound undergoes both melting (crossing the solid liquid equilibrium) and boiling (crossing the liquid gas equilibrium). This compound undergoes solid to liquid and liquid to gas changes. 6. To the right is the phase diagram of water. a) Label each region with the appropriate phase. b) As you go deeper in the ocean, the water gets colder, eventually reaching 0°C. Why do you not observe ice deep in the ocean? Use the information in the phase diagram (and the fact that pressures at the bottom of the ocean are about 1000 times greater than at sea level) in your explanation. It’s a liquid at 1000 atm and 0°C 7. Use the phase diagram of water in the previous problem for the following. a) Label points A-E. A- Triple point B- Critical point C- Normal Melting point D- Normal Boiling point E- Nothing b) Freeze-drying is used to preserve food at a low temperature with minimal loss of flavor. It is accomplished by freezing the food and then lowering the pressure with a vacuum pump to sublime the ice. Must the pressure be lower than the pressure at the triple point of H 2 O? Pressure Temperature Solid A B C D E Liquid Gas

The pressure has to be lower than the triple point; the line separating the solid and gas phases occurs at pressures below the triple point pressure, so if we want the solid H 2 O to vaporize, the pressure must cross below that line. 8. The melting point of solid hydrogen is 15.0 K at 1.00 atm. The temperature of its triple point is 13.8 K at 0.0695 atm. Does liquid H 2 expand or contract when it freezes? Both the temperature and the pressure of the triple point are lower than those of the normal melting point, thus the slope of the solid-liquid line must be positive and the solid phase has a higher density than the liquid phase. Therefore, Hydrogen contracts as it freezes 9. Sketch a phase diagram for material Z, which has a triple point at (152 K, 0.371 atm), a boiling point of 166 K at a pressure of 1.00 bar, and a normal melting point of 161 K at 1 bar.

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Homework 4. Phases and phase changes. Due Friday, July 15th by email. 1. Reading phase diagrams. • 11.89 The phase diagram of sulfur is shown here. (a) How many triple points are there? (b) Monoclinic and rhombic are two allotropes of sulfur. Which is more stable under atmospheric conditions? (c) Describe what happens when sulfur at 1 atm is heated from 80°C to 200°C. P (atm) un 1.0 154°C 1288 atm Rhombic Liquid A 10-5 atm Vapor 95.4°C 119°C 1 (°C) Monoclinic 10 atm

Could you help me with #7? I included a picture of the phase diagram that was given.

The phase diagram of NH3 can be characterized by the following information. The normal melting and boiling points are 195.2 and 239.82 K, respectively; the triple point pressure and temperature are 6077 Paand 195.41 K, respectively. The critical point is found at 112.8 x 105 Pa and 405.5 K. Make a sketch of the P-T phase diagram (not necessarily to scale). Place a point in the phase diagram for the following conditions.State which and how many phases are present.a. 195.41 K, 9506 Pab. 195.41 K, 6077 Pac. 245.5 K, 101325 Pad. 415 K, 115000 Pae. 185.5 K, 6077 Pa

5. Consider the phase diagram of carbon dioxide. What is the pressure at the triple point? ... 73.0 5.11 1.0 -78.5 -56.4 31.1 Temperature ("C) A 1.0 atm B 5.11 atm 10. atm D 73.0 atm Pressure (atm)

Please include phase diagram

(2) Sublimation. Figures below represent the phase diagrams for water and carbon dioxide. (a) Describe the difference in sublimation behavior under the pressure and temperature conditions prevailing on Earth. (b) How would you explain the sublimation of the polar ice caps on Mars during the Martian Summer? 217.7 METING FREZING Normal melting point Solid -Normal boiling point Liquid VAPOURISON COKDENSATION Gas 0.006 SUBLIMATION DEPOSITION 100 374.4 Temperature ("C) Pressure (atm)

Could you help me with #9? I included a picture of the phase diagram that was given.

3-The phase diagram below is for a pure substance. Explain what is wrong with phase diagram a

The following table gives several important points on the pressure-temperature diagram of nitrogen: P (atm) T (K) Triple point 0.123 63.15 Critical point 33.3978 126.19 Normal boiling point 1.0 77.35 Normal melting point 1.0 63.15 Use this information to sketch the phase diagram of nitro- gen. The density of N2(s) is 1.03 g cm-3 and that of N2(€) is 0.808 g cm

Phase Diagrams Phase Diagram - Water Questions #1-5 refer to the phase diagram for water (shown to the right). 1. Which letter (A-E) represents the "triple point"? What does the "triple point" E, 218- mean? liquid C A 1-- solid 0.031. 0.006- B. gas 2. At what pressure can water boil at room temperature (25 • C)? 25 100 374 Temperature (°C) 3. What phase is water found in at room temperature and 1 atmosphere pressure? 4. Water exists in what phase(s) at STP (Standard Temperature and Pressure)? 5. Which of the following phase changes (sublimation, deposition, melting, freezing, condensation, vaporization) occur along the curve BDE? Pressure (atm)

Phase Diagram for Water 1. At a pressure of 1 atmosphere, what is the Solid |Liquid normal freezing point of water? melting vaporization condensation freezing critical point 2. What is the normal boiling point of water, at one atmosphere of water? I atm 3. People in Albuquerque live approximately 5,500 4.58 feet above sea level, which means the normal tom sublimation depesition atmospheric pressure is less than 1 atm. In Gas Albuquerque, will water freeze at a lower temperature or a higher temperature than at 1 100 atmosphere? Will water boil at a 0.0098 higher or lower temperature, than at 1 Temperature (°C) atmosphere? Pressure

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