016 1.0points The phase diagram for carbon dioxide is given below. Solid Liquid Vapor Temperature, K Pressure, atm If the triple point is at 5.1 atm and - 56 ◦ C, at 1 atm and room temperature, 1. gaseous carbon dioxide is the stable phase. correct 2. gaseous carbon dioxide condenses. 3. liquid carbon dioxide is the stable phase. 4. solid carbon dioxide is the stable phase. 5. solid carbon dioxide melts. Explanation: 017 1.0points CarbonDioxide 3 1 4 2 A B 200 250 300 350 400 10 0 10 1 10 2 10 3 10 4 Pressure, bar Temperature, K A sample of carbon dioxide is stored at 10 4 bar and 250 K. This sample is then decompressed to 10 0 bar at constant temper- ature. Then, at constant pressure it is heated
nguyen (dtn564) – Homework 1 – fakhreddine – (49350) 7 to 400 K. Next, it is compressed at con- stant temperature to 200 bar. According to the phase diagram, how many phase transi- tions has the carbon dioxide gone through, and what is its final state? 1. 3, supercritical fluid 2. 2, liquid 3. 2, supercritical fluid correct 4. 3, gas 5. 2, gas Explanation: Navigate through the diagram through each process. In the first decompression, the solid is decompressed and becomes a liquid and then a gas (2 phase transitions). Upon heating, it becomes a supercritical fluid (no phase transitions). 018 1.0points Consider the phase diagrams for water and carbon dioxide. Explain the following observations: A thin wire with weights attached is draped over a block of “dry ice” and a second wire with weights is draped over a block of ice. The wire cuts through the ice but not through the “ dry ice.” 1. The melting point for water is increased and for carbon dioxide reduced with increased pressure. 2. Both melting points are increased with increased pressure. 3. The melting point for water is reduced and for carbon dioxide increased with in- creased pressure. correct 4. Both melting points are reduced with increased pressure. Explanation: For water, increased pressure reduced the melting point whereas for carbon dioxide the opposite is true. Remember, ice is less stable at high pressures. 019 1.0points For a hypothetical substance X, the triple point is at Y ◦ C and Z atm and the critical point of X is at G ◦ C and H atm. Liquid X is less dense than solid X. Which of the following statements about the substance X is NOT true? A phase diagram sketch may be useful. 1. At pressures higher than Z atm, we can cause X to sublime if we raise the temperature carefully enough. correct 2. Liquid X cannot exist at temperatures lower than Y ◦ C, regardless of pressures. 3. At a pressure somewhat above Z atm, the melting point of X would be fairly close to Y ◦ C. 4. At a pressure between Z atm and H atm, the boiling point of X would be greater than Y ◦ C and less than G ◦ C. 5. At Y ◦ C and Z atm, we would have solid X, liquid X and gaseous X in equilibrium.