Three Lab Reports with pre/post lab questions answered for General Chemistry
Jram220
EnthalpyLabReport.docx
Enthalpy and Specific Heat
pre-lab Questions
When 3.0 kg of water is warmed from 10 °C to 80 °C, how much heat energy is needed?
A calorimeter contains 100 g of water at 39.8 ºC. A 8.23 g object at 50 ºC is placed inside the calorimeter. When equilibrium has been reached, the new temperature of the water and metal object is 40 ºC. What type of metal is the object made from?
experiment 1: determination of specific heat of a metal
Data Sheet
Table 2: Mass
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Mass (g) |
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Water |
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Unknown Metal Strip |
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Table 3: Specific Heat Data
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Time (minutes) |
Temperature (°C) |
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Trial 1 |
Trial 2 |
Trial 3 |
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Initial |
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5 minutes |
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6 minutes |
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7 minutes |
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8 minutes |
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9 minutes |
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10 minutes |
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Average Specific Heat Capacity of the Unknown Metal: |
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Post-Lab Questions
1. Why is ΔTmetal < 0?
Why is ΔTwater > 0 ?
A metal sample weighing 43.5 g and at a temperature of 100.0 °C was placed in 39.9 g of water in a calorimeter at 25.1 °C. At equilibrium the temperature of the water and metal was 33.5 °C. Determine the specific heat capacity of the metal.
What is the average specific heat capacity of the unknown metal in this experiment?
What is the unknown metal? Use Table 1 for reference.
experiment 2: cold packs vs. hand-warmers
Data Sheet
Table 4: Cold Pack Data
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Time (sec) |
Temperature (°C) |
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Initial |
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30 |
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60 |
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90 |
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120 |
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150 |
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180 |
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210 |
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240 |
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270 |
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300 |
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330 |
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360 |
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390 |
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420 |
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450 |
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Table 5: Hand Warmer Data
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Time (sec) |
Temperature (°C) |
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Initial |
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30 |
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60 |
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90 |
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120 |
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150 |
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180 |
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210 |
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240 |
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270 |
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300 |
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330 |
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360 |
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390 |
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420 |
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450 |
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Post-Lab Questions
1. Graph the data from Tables 4 and 5 as two separate lines on the same graph and send the graph to your instructor. Construct your graph on a computer program such as Microsoft Excel®. If you do not have a graphing program installed on your computer, you can access one on the internet via the following links: http://nces.ed.gov/nceskids/createagraph/ or http://www.onlinecharttool.com
Calculate the overall temperature change for the cold pack (Tmax - Tmin). Show your work.
Calculate the overall temperature change for the hot pack (Tmax - Tmin). Show your work.
Which pack works by an exothermic process? Use experimental data to support your answer.
Which pack works by an endothermic process? Use experimental data to support your answer.
Write the balanced reaction for the dissociation of ammonium nitrate in water.
Which pack had the greatest change in enthalpy? How do you know?
Describe what would happen to the maximum temperature if the experiment used double the amount of hand warmers. Justify your answer.
Describe if and how the rate of temperature change would be affected if you crushed the cold pack crystals.
Explain how the law of conservation of energy was observed in this experiment.
