nazarali mmn788 Homework 1 fakhreddine 49350 4 diethylether and benzene are 289

Nazarali mmn788 homework 1 fakhreddine 49350 4

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nazarali (mmn788) – Homework 1 – fakhreddine – (49350) 4 diethylether and benzene are 289, 1126, 2680, and 644 torr, respectively. Which of these is NOT above its boiling point at normal atmo- spheric pressure? 1. methanol and diethylether 2. diethylether 3. None of these 4. water 5. water and benzene correct 6. methanol, diethylether, and benzene Explanation: The vapor pressures for water and benzene are still below 760 torr at 75 C, which means that they are not up to the boiling point yet and are in fact, below the boiling point. Methanol and diethylether are well above 760 torr at this temperature which means they are above their normal boiling points. 011 1.0points At 20 C the vapor pressure of dry ice is 56.5 atm. If 10 g of dry ice (solid CO 2 ) is placed in an evacuated 0.25 L chamber at a con- stant temperature of 20 C, will all of the solid sublime? 1. Yes correct 2. No 3. Only if it is at the triple point Explanation: The dry ice will sublime until the pressure is equal to the vapor pressure. There are 0.227 moles of CO 2 . If all sublimes the pressure will be less than the vapor pressure, so the solid will never reach equilibrium with the gas, and the system will be all gas. 012 1.0points The dramatic temperature changes on the moon between day and night are not seen on the Earth because of what property of water? 1. excellent solvent 2. high heat capacity correct 3. less dense as a solid 4. All of these contribute. Explanation: 013 1.0points It is found that 600 J of heat are required to melt 15 g of a compound. What is the heat of fusion of this compound? 1. This cannot be answered without knowing the specific heat of the solid substance. 2. (600) (15) J/g 3. (600) (15) 1000 J/g 4. 600 15 J/g correct 5. (600) (1000) 15 kJ/g Explanation: 014 1.0points The specific heat of water is 1 . 00 cal / g · C, the heat of vaporization of water is 540 cal/g, and the heat of fusion of water is 80 cal/g. How much heat would be required to convert 10 grams of ice at 0 C to 10 grams of water at 75 C? 1. 61.5 kcal 2. 15.5 cal 3. 6150 cal 4. 1.55 kcal correct 5. 155 cal Explanation:
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nazarali (mmn788) – Homework 1 – fakhreddine – (49350) 5 10g H 2 O(s) 0 C step 1 -→ 10 g H 2 O( ) 0 C step 2 -→ 10g H 2 O( ) 75 C Step 1: 80 cal g (10 g) = 800 cal Step 2: 1 cal g · C (10 g)(75 - 0) C = 750 cal Total = 800 cal + 750 cal = 1550 cal = 1 . 55 kcal 015 1.0points Consider an insulated system containing 100 g of liquid water and 100 g of ice at equi- librium under atmospheric pressure. A total of 12 g of steam at +110 C is admitted to the system. What is the phase composition and temperature when equilibrium is reestab- lished? 1. 208 g of water and 4 g of ice at 0.0 C 2. 212.0 g of water at 1.6 C 3. 212.0 g of water at 1.3 C 4. 212.0 g of water at 38.7 C 5. 209.0 g of water and 3.0 g of ice at 0.0 C correct Explanation: m water = 100 g m ice = 100 g m steam = 12 g T = 110 C For these types of problems, it is reasonable to assume that the final temperature must be somewhere between 0 C and 110 C. Given the relatively large amount of ice compared to the steam, the final temperature is likely to be closer to 0 C.
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  • Fall '07
  • Holcombe
  • Chemistry, Mole, mol HCl, Phase transition

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