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Heat (Enthalply) Problem Set

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• 1. Name __________________________ HEAT (Enthalpy) PROBLEMS Block ______ Date ______________ H = m · C · ΔT K = oC + 273 DIRECTIONS: Show the set-up for each problem. Use significant digits. 1. What is the metric unit for heat energy? _______________ 2. What is the relationship between the value of the specific heat constant and the ability of a substance to conduct heat energy? 3. Using the formula for the temperature conversion between Celsius and Kelvin, solve the following temperature problems: (a) 345 K = _________ oC (c) 126 K = ________ oC (b) –37oC = ________ K (d) 147oC = ________ K 4. A granola bar contains 185 nutritional Calories. Convert this energy to calories. (A nutritional Calorie = 1 kilocalorie) 5. A package containing two Reese’s® Peanut Butter Cups supplies 380 nutritional Calories. The Reese’s Cups have a total mass of 70.0 grams. (Hint: Table 15.1) (a) Calculate the amount of Calories per gram supplied by eating one Reese’s® Cup. (b) If you were to completely consume three of these packages of Reese’s Cups, how many heat calories would this produce? 6. How much heat would be required to raise the temperature of 68.0 grams of AlF3 from 25.0oC to 90.0oC? The specific heat for aluminum trifluoride is 0.8948 J/goC.
• 2. 7. If it necessary to use 870 Joules of energy to heat 5.50 grams of olive oil from 21.0oC to 85.0oC, what would be the specific heat of the olive oil? 8. Find the mass of a sample of water that increases its temperature from 277 K to 370 K when it absorbs 5.65 x 105 J of heat. 9. Stainless steel has a specific heat of 0.51 J/goC. If a 155.5 gram piece of stainless steel at 30.0oC absorbs 14,900 J of heat, what will be its’ final temperature? 10. How many Kilojoules of heat is needed to raise the temperature of 200.0 grams of helium gas from –60.0oC to 150.0oC? (The specific heat constant for helium is 5.1931 J/goC.) 11. Explain: In the summer, why does the concrete deck around an outdoor swimming pool become too hot to walk on with your bare feet, while the pool water stays relatively cool. 12. When you read the nutritional label on a food product, it tells you the amount of Calories per serving for that particular food. What do these “Calories” mean? (In other words, what is it really telling you?)
• 3. 13. (a) 75.00 grams of ice is placed into a sealed container. If the ice has a temperature of –8.0oC and it is heated slowly until it reaches 0.0oC, how much heat energy will be needed? (The specific heat of ice is 2.09 J/goC.) (b) The heat of fusion of ice (Hf) is 336 J/g. How many joules of heat will be required to completely melt all of this sample of ice during the phase change? (c) Then, if the newly melted water at 0.0oC is heated until it reaches the boiling point of 100.0oC, determine the amount of heat energy needed for this endothermic change. (The specific heat capacity for liquid water is 4.18 J/goC.) (d) Now, the hot water at 100.0oC begins to boil. If the heat of vaporization for water (Hv) is 2260 J/ g, how much heat energy will be required to completely vaporize all of this water? (e) Once the water has all vaporized, how much heat energy will be needed to heat the steam until it reaches a temperature of 160.0oC. (The specific heat capacity for steam is 2.01 J/goC). (f) FINALLY, determine the grand total of heat energy (H) that is required to change 75.00 grams of ice at –8.0oC to 75.00 grams of steam at 160.0oC?
• 4. 14. Often in late spring, farmers in Florida will spray their orange trees with water so that when the air temperature drops below 32oF (0oC), the water freezes onto the oranges, protecting the fruit from frost damage. How does this process protect the oranges? 15. A beaker containing 150.0 grams of water at 88.0oC is poured into a Styrofoam cup calorimeter with 125.0 grams of water at 3.5oC. The specific heat of liquid water is 4.18 J/goC. (a) What is the final temperature of the system? (b) Determine the heat lost by the warm water. (c) How much heat is gained by the colder water?