213_Lab 3-Fall2021

pdf

School

University of Illinois, Urbana Champaign *

*We aren’t endorsed by this school

Course

213

Subject

Physics

Date

Apr 3, 2024

Type

pdf

Pages

Uploaded by CoachTigerMaster954

©University of Illinois at Urbana-Champaign Physics 213 Lab 3 Summer 2023 Edition Page 1 of 11 Physics 213 --- Lab # 3 Phase Transitions (Using the new PasPort Sensors) Name: ________________________________________________________ Lab Partner(s): __________________________________________________ (indicate who has plots) _________________________________________________ _________________________________________________ Section: __________________ TA: _____________________________ Lab Date: _______________________________ In this lab, we will carry out a series of measurements involving phase transitions. Key Concepts In This Lab:  Phase transitions  Equilibrium vapor pressure  Latent Heat of Fusion  Latent Heat of Vaporization P: /5 L: /15 T: /20

©University of Illinois at Urbana-Champaign Physics 213 Lab 3 Summer 2023 Edition Page 2 of 11 EXPERIMENT # 1 Vapor Pressure of Water Here we see an illustration of the Boltzmann factor in a common practical example. The idea is to make water at different temperatures boil (T), by reducing its pressure (P) . You’ll find out at which pressure it boils, therefore, what value of water vapor is in equilibrium with liquid water at different temperatures . You’ll reduce pressure just by pulling back on the plunger of a syringe until the water starts to boil, which will make it hard to reduce the pressure any further. Follow the directions carefully. Read the whole procedure before you start to minimize possibility of mistakes. The aim is for you to measure the vapor pressure at two points – one around 45°C and another around 65 to 70°C. For your graph, you’ll use these two measurements along with the vapor pressure for 0°C (which you can assume to be 0.61 kPa) and the vapor pressure for 100°C (which you should know). 1. This experiment uses the same temperature sensor you used in part 1 of this lab and a pressure sensor. Connect and set up the ‘ Type K Temperature sensor ’ to PasPort 1 and the Absolute Pressure sensor to PasPort 2. 2. Open the file: “ P213-Lab3_Experiment 1 - PasPort Sesnsors.cap ” . 3. Click on the “Record” button to continuously display temperature and pressure.

©University of Illinois at Urbana-Champaign Physics 213 Lab 3 Summer 2023 Edition Page 3 of 11 4. Get exactly 1.5 cups of room temperature water in the large Pyrex glass measuring cup (with the handle) from the container at the sink marked “room temperature water for part 1 ”. Heat Pyrex measuring cup of water in one of the microwave ovens for 1 minute. Continue to check temperature until water reaches 45 ° C. 5. Record the temperature in the table below. Fill the syringe containing approximately six Teflon chips with about 15 mL of water. This should fill half of the length of the tube. Hold the syringe with the Luer-lok side up and the hose extended upward. Tap the syringe to get as many of the tiny air bubbles in it to rise to the Luer-lok opening. Hold the tubing over the Pyrex measuring cup; push out the water to around 25 mL to continue process of bubble elimination. 6. Quickly connect the syringe to the Absolute Pressure sensor without letting any air back into the tubing. DO NOT PUSH WATER INTO THE PRESSURE SENSOR! THE WATER WILL BREAK THE PRESSURE SENSOR!! One lab partner will determine when the boiling begins and alert another lab partner who will note the pressure. Lab members will rotate into each task for at least two recordings. 7. Quickly lay the syringe on its side on the lab table. Tap the syringe a bit to spread out the Teflon chips. With one hand holding the syringe securely on the table, steadily pull back the plunger while watching the bubbles form on the Teflon pieces in the syringe. Say “now” at the exact moment that you see a bubble rise off the beads so your partner can simultaneously note the pressure. Record the pressure in the table below. 8. Disconnect tubing from the pressure sensor and push the water from the syringe into a beaker/measuring cup. Rotate with a lab partner repeating steps 4 through 7. If there’s time take a third reading with another lab partner operating the syringe. 9. Next, heat the water to around 67 ° C. Heat Pyrex measuring cup of water in one of the microwave ovens for 1 minute. Continue to check temperature until water reaches 67 ° C. 10. Follow steps 4 through 8 above with the 67 ° C water.

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

©University of Illinois at Urbana-Champaign Physics 213 Lab 3 Summer 2023 Edition Page 4 of 11 T ( o C) T (K) 1/T (1/K) P (kPa) 100 373 101.3 0 273 0.61 11. Plot p vs. 1/T (absolute T, of course!) on the attached semi-log graph. Draw a straight line that best describes your data. 12. When completed with Experiment 1, delete the data for this run by clicking on the “Delete Last Run” button. 13. Close the file. DO NOT SAVE THE FILE!!! THEORY: It’s a decent approximation to say that the temperature dependence of the equilibrium vapor pressure comes mainly from the Boltzmann factor for the relatively high-energy states of the vapor states. A more precise treatment (the Clausius-Clapeyron equation) gives: p = p 0 exp(-L/kT) or ln(p/p 0 ) = -L/kT or ln(p) = -L/kT + constant where the latent heat L per molecule is almost but not exactly the same as the average extra energy,  E, of a gas molecule above a liquid molecule, and p 0 is a fixed pressure which can be inferred from your data.

©University of Illinois at Urbana-Champaign Physics 213 Lab 3 Summer 2023 Edition Page 5 of 11 ANALYSIS: When you plot ln(p) vs. 1/T, what should the slope be according to the Clausius- Clayperon equation, in terms of L, k, and T? ______________________________________________________________ ______________________________________________________________ Does your data fit the expected form (linear on the semi-log plot)? ______________________________________________________________ ______________________________________________________________ Pick two convenient points on your straight line. Label them P 1 and P 2 . Read off and enter below the values of p and 1/T at each point. At point 1, P 1 = _________ and T 1 = _________ . At point 2, P 2 = __________ and T 2 = _________. The slope is given by: 2 1 2 1 ln ln 1 1 P P T T   This should equal – L/k. What actual slope did you find? _______________________________________________________________ Estimate what is the experimental uncertainty in the slope, given the scattering of the data? ______________________________________________________________ ______________________________________________________________ What then is L, the latent heat per molecule? Compare your measured value to the book value of 0.42 eV. _ ______________________________________________________________________________ _____________________________________________________________________________ _ _ _______________________________________________________________________________ _______________________________________________________________________________

©University of Illinois at Urbana-Champaign Physics 213 Lab 3 Summer 2023 Edition Page 6 of 11 EXPERIMENT # 2 Measuring the Latent Heats of Fusion and Vaporization In this experiment, we will measure the latent heat of vaporization of nitrogen, L V and the latent heat of fusion of water, L F . 1. Locate the force sensor that is mounted vertically on the ringstand. Connect the Force Sensor to Channel C of the Pasco Interface. Leave the ‘Absolute Pressure/Temperature’ & ‘Type K Temperature’ Pasport Sensors attached to the Pasco interface. 2. Open the file: “ P213-Lab3_Experiment 2 - PasPort Sensors.cap ” . 3. Fill the ice bucket with a mixture of ice and water to a depth of about 4”. Stir the ice and water to bring it into thermal equilibrium. Fill the glass beaker with the chilled water (no ice!!!) to about the same level as the ice bath and place it in the ice bucket. The goal is to maintain a water bath at 0  C. Force sensor liquid nitrogen aluminum disk

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

©University of Illinois at Urbana-Champaign Physics 213 Lab 3 Summer 2023 Edition Page 7 of 11 4. Locate the aluminum disk attached to a string. Measure its mass and record it in the table below. 5. Ask assistance from your TA to fill your large Styrofoam cup with Liquid Nitrogen (LN 2 ), to full. Hang the large Styrofoam cup from the hook below the force sensor. Predictions: What do you predict will happen to the LN 2 when you immerse the aluminum cylinder in the LN 2 ? In particular, how will the mass of LN 2 in the Styrofoam cup change? Why? ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ If you next move the aluminum cylinder from the LN 2 to the chilled water bath, what do you predict will happen? Why? ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ 6. Test your predictions. Press the “tare” button on the side of the force sensor to zero it. 7. Start the data acquisition by clicking the “Record” button. Safety Precautions for using Liquid Nitrogen (LN 2 ) 1. Do not touch LN 2 or any objects cooled in it --- the temperature of LN 2 at atmospheric pressure is 77K = -196  C. It can cause severe cold burns. 2. Never seal LN 2 in a closed container --- it expands dramatically in volume when it vaporizes at atmospheric pressure. 3. Handle LN 2 carefully --- it splashes easily when it comes into contact with a warm surface. This especially applies when you are pouring LN 2 into other containers, and submersing warm objects into the liquid. 2 3 3 4

©University of Illinois at Urbana-Champaign Physics 213 Lab 3 Summer 2023 Edition Page 8 of 11 8. After 30 seconds have elapsed, hold the aluminum cylinder by the string and lower it slowly and carefully into the LN 2 until it is fully submersed. Avoid touching the cylinder on the bottom or side of the cup. 9. Keep the aluminum cylinder submersed at all times. When the LN 2 stops boiling (it will boil most vigorously just before it stops), wait 30 additional seconds before stopping the data acquisition, but keep the cylinder submersed. 10. As quickly as possible, remove the aluminum cylinder from the LN 2 and submerse it into the chilled water bath. (Note: do not hold the cylinder too close to the bottom or sides of the beaker!) Ice will form on the surface of the cylinder. Keep the cylinder submersed in the water for at least 2 minutes. 11. Remove the cylinder from the water and place it into a small Styrofoam cup. Weigh the ice-coated cylinder (the mass of the cup is negligible). THEORY: The latent heat of a material is the amount of heat energy (per unit mass) required to change the state of that system from one phase to another at constant temperature: L V = latent heat of vaporization …… change from liquid t o gas L F = latent heat of fusion …… change from liquid to solid

©University of Illinois at Urbana-Champaign Physics 213 Lab 3 Summer 2023 Edition Page 9 of 11 In the first part of this experiment, the energy required to vaporize the liquid nitrogen comes from the thermal energy of the cylinder as it cools from room temperature T room to the boiling point of LN 2 (T LN = 77 K): ( ) LN V Al Al room LN E m L m c T T     . Here, we have made the simplifying assumption that the specific heat of aluminum, c Al , is independent of temperature. This is in fact not true – it changes by more than a factor of 2 over this temperature range – as shown in the figure below (n.b. 1 kcal = 4186.8 Joules): In order to carry out this experiment properly, we would need to continuously measure both the mass of the LN 2 and the temperature of the aluminum cylinder as it cools in the LN 2 and integrate the above relation. This would be experimentally more complex to carry out! Fortunately, most of the LN 2 boil-off occurs at the higher temperatures. Thus, using the approximation that c Al is independent of temperature (with a value ~900 J/kg-K), then from measuring the total mass of LN 2 boiled off, the latent heat of vaporization of nitrogen is: ( ) Al Al room LN V LN m c T T L m   . In the second part of this experiment, ice forms on the surface of the aluminum cylinder until it warms up to the water bath temperature (0  C). The heat energy required to warm the aluminum cylinder comes from the latent heat of fusion: ( ) ice F Al Al bath LN E m L m c T T     .

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

©University of Illinois at Urbana-Champaign Physics 213 Lab 3 Summer 2023 Edition Page 10 of 11 Note that here again, we have used the simplifying assumption that the specific heat of aluminum, c Al is constant over this temperature range. Thus, from the mass of ice formed, the latent heat of fusion of water is: ( ) Al Al bath LN F ice m c T T L m   . ANALYSIS: 1. From the graph of Force vs. time, find the total change in the weight of the liquid nitrogen and the mass that boiled off. Record this value below. 2. Calculate the latent heat vaporization of nitrogen. Record in table below. 3. From the mass change of the block, find the mass of ice formed. 4. Calculate the latent heat of fusion of water and record it in the table below. M Al (kg)  F (N) m LN (kg) L V (calculated) (J/kg) L V (book value) (J/kg) 2.00 x 10 5 M Al+ice (kg) m ice (kg) L F (calculated) (J/kg) L F (book value) (J/kg) 3.33 x 10 5 5. When completed with Experiment 2, delete the data for this run by clicking on the “Delete Last Run” button.

©University of Illinois at Urbana-Champaign Physics 213 Lab 3 Summer 2023 Edition Page 11 of 11 6. Close the file. DO NOT SAVE THE FILE!!! Questions: How did your measurements of the latent heats compare with book values? What are possible sources of errors? ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ Why does the LN 2 boil most vigorously just before it comes into thermal equilibrium with the cylinder? (Hint #1: Does vapor or liquid have a higher thermal conductivity; think about being exposed to 0  C air or 0  C water. Hint #2: It may help you to first answer the next question.) ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ You may have noticed that the water freezes more slowly on the cooled cylinder once an ice layer is formed? Why is this? ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ FINISHING UP: When you are finished with the lab, please carry out the following clean-up steps: 1. Empty all water containers and dry up any spills or drops. Ask the TA to discard your remaining liquid nitrogen. 2. Stack all equipment, samples, and tools neatly on your table. 3. Attach the graphs {ln( p) vs. 1/T (included in this write-up) } that you have plotted to the back of your lab write-up and hand it in to your lab TA. In short, leave the lab as you found it -- or would have wanted to find it.

213_Lab 3-Fall2021

Related Documents