Instructions for Working out the Worksheets: Work in groups of 4 on these problems. You should try to answer the questions without referring to your textbook. If you get stuck, try asking another group for help. Your TA will come around when needed to help guide you if needed. Round Robin Instructions: 1. Each group member will be assigned a number, starting with #1 and ending with the number of people in the group. 2. Student #1 will read the question aloud and define the information needed to solve the problem, create an outline on how you can solve the problem. 3. When the group agrees that the necessary information is complete, student number two will do the first mathematical step. When the group agrees that the step is correct, student number three will do the next step. Continue this way until the group agrees that the given answer had been correctly converted to the wanted answer. 4. Student #2 will start the next question by reading it aloud as in #1. Follow this pattern for all the questions in the session. Topics being Covered in the Worksheet: Specific Heat Capacities of Common Substances: Substance J/g O C Water (l) 4.184 Water (s) 2.03 Water (g) 2.0 Aluminum (s) 0.89 Iron (s) 0.45 Mercury (l) 0.14 Carbon (s) 0.71 Silver (s) 0.24 Gold (s) 0.13 4.184 Joules = 1 calorie 1. Calorimetry 2. Hess s Law 3. Heat of Formation 1-18 In the following problems you will be solving mathematical problems to help you understand topic 1. Make sure you have the correct significant figures for each problem. q = mcδt or q = -q -mcδt = mcδt 1. Determine the amount of heat energy in joules required to raise the temperature of 7.40 g of water from 29.0 ºC to 46.0 ºC. 2. Calculate the joules of energy required to heat 454.3 g of water from 5.4 ºC to 98.6 ºC. 1 of 9
3. How much heat must be added to 8.21 g sample of gold to increase its temperature by 6.2 ºC? The specific heat of gold is 0.13 J/g ºC. 4. When a 25.7 g sample of NaI dissolves in 80.0 g of water in a calorimeter, the temperature rises from 20.5 ºC to 24.4 ºC. Calculate H for the process. NaI (s) Na + (aq) + I (aq) 5. A 2.50 g sample of zinc is heated, then placed in a calorimeter containing 65.0 g of water. Temperature of water increases from 20.00 ºC to 22.50 ºC. The specific heat of zinc is 0.390 J/g ºC. What was the initial temperature of the zinc metal sample? 6. What quantity of energy (in J and cal) is required to heat a piece of iron weighing 1.31 g from 25.0 ºC to 46.0 ºC? 2 of 9
3. How much heat must be added to 8.21 g sample of gold to increase its temperature by 6.2 ºC? The specific heat of gold is 0.13 J/g ºC. 4. When a 25.7 g sample of NaI dissolves in 80.0 g of water in a calorimeter, the temperature rises from 20.5 ºC to 24.4 ºC. Calculate H for the process. NaI (s) Na + (aq) + I (aq) 5. A 2.50 g sample of zinc is heated, then placed in a calorimeter containing 65.0 g of water. Temperature of water increases from 20.00 ºC to 22.50 ºC. The specific heat of zinc is 0.390 J/g ºC. What was the initial temperature of the zinc metal sample? 6. What quantity of energy (in J and cal) is required to heat a piece of iron weighing 1.31 g from 25.0 ºC to 46.0 ºC? 2 of 9
7. A 5.63 g sample of solid gold is heated from 21.0 ºC to 32.0 ºC. How much energy (in J and cal) is required? 8. A 1.60 g sample of a metal that has the appearance of gold requires 5.8 J of energy to change its temperature from 23.0 ºC to 41 ºC. Is the metal pure gold? 9. A 2.80 g sample of pure metal requires 10.0 J of energy to change its temperature to 15.0 ºC. What is this metal? 10. How much heat energy is required to raise the temperature of a 30.0 g sample of aluminum from 15.0 ºC to 35 ºC? 11. What would be the temperature change of a 24.2 g sample of carbon if 575.6 J of heat energy was applied? 3 of 9
12. A sample of water raised its temperature from 45.7 ºC to 89.9 ºC when 4.36 kj of heat energy was applied. What is the mass of the water sample? 13. A 450.0 g sample of silver was cooled from 125.0 ºC to 45.0 ºC. How much heat energy did the sample lose? 14. A sample of iron having a mass of 93.3 g is heated to 65.58 ºC is placed in 75.0 g of water raising the temperature from 16.95 ºC to 22.24 ºC. Find the specific heat capacity for this iron sample. The answer you find has some lab errors due to human mistakes. Find your percent error. 15. What is the resulting temperature when 35 g of water at 75 ºC is mixed with 15 g of water at 15 ºC? 4 of 9
16. If I burn 0.315 moles of hexane (C6H14) in a bomb calorimeter containing 5.65 liters of water, what s the molar heat of combustion of hexane if the water temperature rises 55.4 ºC? 17. If I burn 22.0 g of propane (C3H8) in a bomb calorimeter containing 3.25 liters of water, what s the molar heat of combustion of propane if the water temperature rises 29.5 ºC? 18. When a 1.000 g sample of rocket fuel hydrazine, N2H4, is burned in a bon calorimeter, which contains 1200. g of water, the temperature rises from 24.62 ºC to 28.16 ºC. If the heat capacity for the bomb is 840. J/ºC, calculate: a. qrxn for combustion of a 1.000 g sample b. qrxn for combustion of one mole of hydrazine in the bomb calorimeter. 5 of 9