Lab 5 Heat (1)

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Metropolitan State University Of Denver *

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1055

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Chemistry

Date

Jul 1, 2024

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pdf

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Uploaded by SuperCrownJaguar49

Part 1- Conduction: Prediction: I predict that the pad of butter on the metal spoon will fall first. Explain: Metal conducts heat more than plastic, so the heat from the water will spread through the metal spoon faster than the plastic spoon. 1. Was your prediction correct? Yes, my prediction was correct. 2. Explain how the heat got from the water to the butter. Describe what is happening to the particles the spoons are made of. The hot water transfers heat to the spoons through conduction: the molecules of the spoon start to vibrate more rapidly as they gain energy from being in direct contact with the water. These vibrations, and the energy itself, slowly makes its way up the spoon by increasing the vibrations of the molecules it comes in contact with. 3. Why does 1 spoon conduct heat better than the other? Do a bit of research here. Do not just say, “because one is metal and the other is plastic.” Because metal has free electrons, it’s able to transfer energy from one part of the spoon to another. The entropy of the part of the spoon in the water gradually moves up the spoon, so the increased vibrations also move. Plastic is an insulator and lacks free electrons, so it has to rely solely on the vibration of molecules, thus making the energy travel much slower. Part 2- Convection: 1. Describe in detail why this groovy room decoration works. The lightbulb in the lamp generates heat, making the bottom of the mixture warm. When the mixture is warmed, it expands because the molecules begin to vibrate at a higher frequency than they do when at rest. The warmer mixture rises to the top of the lamp because as the mixture expands it also becomes less dense, and thus becomes more buoyant than the cooler water so it rises to the top. The cycle repeats because the cooler water at the bottom begins to heat from the lightbulb and the warmer water that rose to the top becomes cooler since it’s no longer in contact with the bulb. 2. Fill 1 beaker with cold water and a second with an equal amount of warm water. Record the initial temperature of each. warm water: 99°F cold water: 55°F 3. Put 5 drops of chilled dye in each beaker. 4. Watch the dye in each beaker and time how long it takes for the dye to diffuse throughout each beaker. Record the time. warm water: 1:12 min cold water: 14:47 min Questions: 1. In which beaker did the dye diffuse the fastest? Why? The dye in the cold water beaker diffused quicker. This is because of convection current: the water in the warm water has faster molecules, so the dye was able to spread faster. 2. Did you notice a pattern to how the dye moved in the liquid? Was it different for the 2 cases? The dye in the warm water didn’t have a pattern, it just spread out as the dye hit the water. However, the dye in the cold water left streaks as it entered and expanded in clouds.

3. Watch the video at Convection Current Demonstration . Then explain how convection moves heat from 1 place to another and how this explains the other activities or videos in this section. Heat moves from one place to another through convection currents, similar to what was seen with the lava lamps. Convection currents occur when gas or liquid is heated and becomes less dense. The warm, or less dense, water travels to the top and eventually cools off, while the cooler, more dense water sinks to the bottom and eventually warms up from the lamp and will rise to the top. This creates a cycle, or a current, from the convection. Part 3- Radiation: Object 1(Black) Object 2(Silver) Time Temperature Time Temperature 1 min 70 °F 1 min 68 °F 2 min 71 °F 2 min 68°F 5 min 74 °F 5 min 69°F 7 min 76°F 7 min 70°F 10 min 80°F 10 min 71 °F 15 min 85°F 15 min 73°F 20 min 92°F 20 min 76°F 1. Determine the total change in temperature for each can: Temperature change in black can: 22°F Temperature change in silver can: 12°F 2. What happens to the thermal radiation that falls on each of the cans? Is it absorbed or reflected? Black: Absorbed Silver: Reflected 3. Most objects are not perfect emitters, so the emissivity e is not equal to one, but some value less than 1. Which object above has a higher value of emissivity? Black can Silver can Part 4- Heat and Energy Conservation: Amount of sand Time Starting Temp. Final Temp. Temp. Change Half cup 1 min 68 °F 74 °F 6 °F

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