Module 06 — Heat and Particles · quiz worth 30 pts
The lab becomes easier when each water sample is treated as its own system.
Tf is above Ti, so ΔT and Q are positive. Energy enters.
Tf is below Ti, so ΔT and Q are negative. Energy leaves.
In the ideal model, the positive and negative amounts cancel. Real lab values differ because the setup is not perfectly isolated.
The Physics Classroom calorimetry tutorial reviews the energy-balance method. The Canvas worksheet and rubric still control this submission.
Should the hot-water Q sign be positive or negative?
Negative, because the hot water loses energy.
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| Trial | Cold water | Hot water | Final temperature |
|---|---|---|---|
| 1 | 250 mL at 20 °C | 250 mL at 98 °C | 56 °C |
| 2 | 200 mL at 20 °C | 400 mL at 98 °C | 72 °C |
| 3 | 300 mL at 15 °C | 150 mL at 90 °C | 41 °C |
The manual route uses two Styrofoam cups, a thermometer, a measuring cup, equal 237 mL samples of hot and cold tap water, and careful timing. The virtual route uses the three supplied trials and requires you to build your own clear data table. Download and use the worksheet for the route you select. Do not combine manual measurements with virtual-trial values.
Hot tap water can burn. Pour slowly, keep the cup stable, and do not use boiling water. Read the entire procedure before starting. Measure both initial temperatures promptly, mix the water, cover the mixture with the inverted empty cup, and record the stable final temperature while keeping the thermometer bulb in the water.
237 mL of water is about 0.237 kg.
Cold water normally has positive ΔT; hot water normally has negative ΔT.
Use cwater = 4186 J/(kg·K), mass in kg, and Q in J.
In a perfectly isolated exchange, magnitudes match.
Put 237 mL of cold water in one cup and 237 mL of the hottest safe tap water in the other. Keep the second cup ready to become a lid.
Measure the cold and hot temperatures quickly. Label each value clearly.
Pour hot into cold, place the thermometer in the mixture, and invert the empty cup over it to reduce exchange with the room.
Check about every 20 seconds until the reading stabilizes. Record that as Tf.
Convert each 237 mL sample to 0.237 kg, calculate both ΔT values and Q values, then compare |Qhot| with Qcold.
Build a table with separate columns for cold volume, cold initial temperature, hot volume, hot initial temperature, final temperature, both masses, both ΔT values, and both Q values. The three trials are supplied below exactly as the course gives them.
Compare energy gained by cold water with energy lost by hot water.
These invented values are not one of the assigned trials. The water samples alone do not balance perfectly, which can represent energy absorbed by the calorimeter or exchanged with the surroundings plus measurement uncertainty.
Do the two water samples on separate lines.
Both use c = 4186 J/(kg·K), but each has its own mass and ΔT.
Do not erase the negative hot-water result. It records direction.
The remainder estimates energy outside the water-only model plus measurement uncertainty.
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State that the lab examined thermal-energy transfer and conservation while hot and cold water approached equilibrium.
Use your own Q values. Say which sample gained energy, which lost energy, and how closely the magnitudes agreed.
Include at least one measured temperature and one calculated energy comparison from your chosen route.
Name a mechanism and its likely effect: heat lost to air, energy absorbed by the cup or thermometer, delay in reading temperature, unequal volumes, or thermometer precision.
Use three short paragraphs if one long paragraph gets tangled.
Purpose of mixing the samples.
Your calculated result and whether energy gains and losses were close.
One specific source of error and the direction it would push a measurement.
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These questions check the procedure and analysis without filling in the worksheet for you.
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