solution_pdfHW1 - nguyen(shn254 – H01 Physical Equilibria...

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Unformatted text preview: nguyen (shn254) – H01: Physical Equilibria – mccord – (51175) 1 This print-out should have 26 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points Substance A has undergone a phase tran- sition (under constant pressure) where ΔH = 10kJ / mol and ΔS = 36J / K · mol. What phase transition could have occurred? 1. deposition 2. freezing 3. melting correct 4. condensation Explanation: Melting is the only phase transition listed where both ΔH and ΔS are positive values. Condensation (gas to liquid), freezing (liqid to solid) and deposition (gas to solid) all have a negative ΔH and ΔS. 002 10.0 points Rank the following in order of increasing va- por pressure at a fixed temperature: H 2 O, CH 3 Cl, He, NaCl 1. NaCl < H 2 O < CH 3 Cl < He correct 2. H 2 O < CH 3 Cl < He < NaCl 3. NaCl < CH 3 Cl < H 2 O < He 4. H 2 O < NaCl < CH 3 Cl < He 5. He < H 2 O < CH 3 Cl < NaCl Explanation: 003 10.0 points Answer the following about CO 2 using the provided phase diagram. What answer choice best describes the tem- perature at the triple point and critical point for CO 2 (triple point temperature, critical point temperature)? Carbon Dioxide 3 1 4 2 200 250 300 350 400 10 10 1 10 2 10 3 10 4 Pressure,bar Temperature, K 1. Not enough information 2. 220 K, 220 K 3. 220 K, 310 K correct 4. 310 K, 310 K 5. 310 K, 220 K Explanation: 004 10.0 points Which of the following constants are needed to calculate the change in enthalpy (ΔH) for heating a sample of liquid water at 10 o C to steam at 150 o C. I) the heat capacity of water II) the enthalpy of fusion of water III) the heat capacity of ice IV) the enthalpy of vaporization of water V) the heat capacity of steam 1. I and V only 2. I and III only 3. II and III only 4. I, IV and V only correct 5. I, II and III only nguyen (shn254) – H01: Physical Equilibria – mccord – (51175) 2 6. I, II, IV and V only 7. I, II, III, IV and V Explanation: The heat capacity of water is necessary to calculate heat needed to raise the liquid wa- ter’s temperature from 10 o C to 100 o C. The enthalpy of vaporization of water is necessary to calculate the heat needed to convert 10 gram of water at 100 o C to 10 grams of steam at 100 o C. Finally, the heat capacity of steam is necessary to calculate heat needed to raise the steam’s temperature from 100 o C to 150 o C. 005 10.0 points Which of the phase changes below might have a ΔS =- 45 . 4 J · mol − 1 · K − 1 ? 1. melting 2. sublimation 3. evaporation 4. freezing correct Explanation: For all phase changes, the signs of both ΔH and ΔS are the same. Because ΔS is negative, we can infer that the phase change in question must be exothermic. Of the answer choices, freezing is such a phase change....
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solution_pdfHW1 - nguyen(shn254 – H01 Physical Equilibria...

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