4 hydrogen bonding between the water molecules 5 the

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4. Hydrogen bonding between the water molecules. 5. The water gets more ”organized” around the ions, expecially small, multiply charged species. CORRECT Explanation: With high carge density ions, the water can be well organized in the hydration sphere thus producing a more orderly (lower entropy) molecular system. 015 2.9points Assume that the temperature is 25 degree C. Water from a local stream is added to one side of the U-tube shown below. Pure water is placed in the tube on the other side of the semipermeable membrane. With the left side open to barometric pressure of 1.0 atm and 1.15 atm applied to the right side, the two liquids do not move.
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Version 023 – Exam 1 – holcombe – (51395) 5 1.00 atm 1.15 atm B A What is the effective molarity ( i.e. , molarity of “particles” such as cations, anions, etc. ) responsible for this osmotic pressure from the natural water from the local stream? You can assume the van’t Hoff factor is one. 1. 0.03 molar 2. 6 × 10 5 molar 3. 0.006 molar correct 4. 0.2 molar Explanation: 016 2.9points The vapor pressure of water at 37 C is 47.1 torr and its enthalpy of vaporization is 44.0 kJ · mol 1 . Estimate the vapor pressure of wa- ter at 87 C. Assume the enthalpy of vaporiza- tion of water is independent of temperature. 1. 713 torr 2. 112 torr 3. 52 torr 4. 503 torr correct 5. 256 torr Explanation: T 1 = 37 C + 273 . 15 = 310 . 15 K T 2 = 87 C + 273 . 15 = 360 . 15 K Δ H vap = 44 . 0 kJ · mol 1 P 1 = 47 . 1 torr Using the Clausius-Clapeyron equation, ln parenleftbigg P 2 P 1 parenrightbigg = Δ H vap R parenleftbigg 1 T 1 - 1 T 2 parenrightbigg = 44 kJ · mol 1 8 . 314 J / mol 1 · K 1 · 1000 J 1 kJ × parenleftbigg 1 310 . 15 K - 1 360 . 15 K parenrightbigg = 2 . 36896 P 2 P 1 = e 2 . 36896 P 2 = P 1 e 2 . 36896 = (47 . 1 torr) e 2 . 36896 = 503 . 323 torr 017 2.9points 018 2.9points Which of the following would raise the vapor pressure of a sample of hexane in a closed container? I) adding more liquid to the container II) decreasing the size of the container III) adding a non-volatile solute to the liquid 1. I only 2. II and III 3. none correct
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Version 023 – Exam 1 – holcombe – (51395) 6 4. I and II 5. II only 6. III only 7. I and III Explanation: Because evaporation is always an endother- mic process, a substances vapor pressure al- ways increases with increasing temperature. Adding a non-volatile solute to any substance will decrease its vapor pressure. Factors such as sample size and container size do not influ- ence the vapor pressure. 019 2.9points According to thermodynamics, which of the following would BEST describe a spontaneous reaction? 1. Δ G is positive and Δ H and Δ S are neg- ative. 2. Δ H is negative. 3. Δ G is negative and Δ H is positive. cor- rect 4. Δ H is positive and Δ S is negative. 5. Δ G is positive and Δ S is positive. Explanation: Δ G must be negative for a spontaneous process.
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  • Fall '07
  • Holcombe
  • Chemistry, Vapor pressure, Torr, pressure cooker, Law of Partial Pressure

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