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Thermodynamics Practice

Thermodynamics Practice.

heather-noble
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Thermodynamics Practice

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  1. Thermodynamics Practice

  2. Slick Rick is offering a “good deal” on platinum coins. He proffers a one ounce (28.3 g) platinum coin to you for a mere $175, a real steal. You know that he is smart enough not to try to slip you a different weight coin, but you suspect that perhaps the coin is just plated with platinum. You “accidentally” drop the coin in your precisely 50.0 mL of coffee in a Styrofoam cup that you only drink at 60.0C. If the temperature drops to 57.6C, is the coin likely real? Hint: This will not be given on the exam. It is the conversion factor between J and calories though. Specific Heat of Platinum: 0.13 J/gK Specific Heat of Water: 4.184 J/gK What is the specific heat of the coin? Is it the value of platinum?

  3. 0kJ (coffee cup) Cm= - mwCwDTw mmDTm Cm= - 50.0g (4.184 g/JC) (60.0C - 57.6C) 28.3 g (57.6C - 21C) Finding Specific Heat First Law of Thermo: = q water + q metal + q cal DE = 0 q metal = mmCmDTm q metal = -q water q water = mwCwDTw mmCmDTm= - mwCwDTw = .48 g / J C

  4. 0kJ (coffee cup) Lithium chloride dissolving in water is an exothermic reaction. If 3.45 g of solid lithium chloride is dissolved in 85.7 mL of water in a coffee cup calorimeter, and the temperature of the water goes from 21.0C to 29.6C, what is the DHsol for LiCl? First Law of Thermo: = q water + q rxn + q cal DE = 0 q rxn = -q water q water = mwCwDTw What amount of energy was absorbed by the water? q rxn = n DHrxn Note: This looks exactly like other phase changes!

  5. Trinitroglycerin, C3H5N3O9, is an explosive. The enthalpy of decomposition (below) at 1 atm pressure is -1541.4 kJ/mol. What is the DHf for nitroglycerin? Need to balance the reaction!

  6. DHrxn = S(DHfprod) – S(DHf react) = = 1.5 DHf N2 + 3DHf CO2 + 2.5DHf H2O + .25 DHf O2 – DHf Nitro -1541.4 kJ =(0) + 3mol(-393.5 kJ/mol) + 2.5mol (-285.8kJ/mol) + 0 – DHf Nitro DHf Nitro = -353.6 kJ/mol

  7. The heat of combustion of fructose, C6H12O6, is -2812 kJ/mol. If a fresh golden delicious apple weighing 4.23 oz (120 g) contains 16.0 g of fructose, what Caloric content does the fructose contribute to the apple? 1 calorie = 4.184 J; 1 Dietary Calorie = 4.184 kJ

  8. Hess’s Law Using the following reactions and enthalpies: What is the DHrxn for the following process (give answer in kJ):

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