Chem 112 Lab 3 - lab 3 PDF

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lab 3...

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Title: GAS THERMOMETRY

Purpose: The purpose of this experiment is to define the physical concept of temperature and absolute zero. As well, to observe how ideal gas molecules behave according to the ideal gas law. Lastly, to understand the relationship between pressure, volume and temperature in gases using gas thermometry.

Introduction: Temperature is a measurement of thermal energy. Thus, when we read a thermometer we are reading how much thermal energy an object has. This thermal energy comes from the many interactions of tiny molecules that are constantly smashing into each other and the sides of their container. This occurrence can be defined by three basic gas laws, Boyle’s Law which states that at constant temperature, the pressure P, of a gas varies inversely with its volume V, or PV= constant; Charles’s Law which states that at constant pressure, the volume of a gas is directly proportional to its absolute (Kelvin) temperature T, V/T = constant. Lastly, when both of these laws are combined they create the ideal gas law which is PV= nRT, where n is the number of gram-moles of the ideal gas and R is the universal gas constant. Using these ideas we will experiment with the ideal gas laws, playing with three different scenarios, increasing pressure, increasing temperature, and lastly a variable volume. From studying these scenarios we will see how each affects the variables of Pressure, number of moles, volume, and temperature. In the following experiment, an arbitrary temperature scale will be created. Any temperature scale is based off of reference points, such as, freezing or boiling points of water. For example, in Celsius water freezes at 0 and boils at 100 degrees. However, our neighbours to the south would measure water freezing at 32 degrees Fahrenheit and boiling at 212 degrees Fahrenheit. We can see the value of degrees is much larger in Celsius than Fahrenheit. Seeing that there can be multiple values for the measurement of temperature it is quite easy to create your own temperature scale. In this experiment we will use reference points in order to create our own arbitrary temperature scale and justify if it is accurate using our gas laws and our known absolute zero value.

Materials: • • • • • • • • • • • •

Lab coat Goggles Heavy duty gloves Dipper Stand to hold dipper Container to hold gas Tap attached to gas container to release gas into container Argon gas Helium gas Boiling water reservoir Ice water reservoir Boiling nitrogen reservoir

• • • •

Vacuum pump Pressure gauge Computer for Graphing Burner

Procedure: 1. Put on lab coat safety goggles and proceed to your gas thermometry work bench. 2. Turn on vacuum pump 3. Pick up dipper, and empty the tank of any residual gas, make sure to close the valve after emptying to ensure any newly inserted gas does not leave the tank. 4. Insert argon gas into the tank until it measures zero (This will be your initial pressure). 5. Put the dipper back on the stand. 6. Put on the heavy duty gloves. 7. Start boiling the water in your reservoir, once the water is boiling place your dipper into the reservoir and record your first reference point. The reference point is created from when the pressure on the graph reaches equilibrium. 8. Now place the dipper into the ice water to get your second reference point. 9. Place the dipper in the boiling nitrogen to get the third reference point. 10. Take the dipper out of the boiling nitrogen and place it back into the boiling water again. This verifies the point in the pressure-temperature graph, reduces the temperature of the dipper faster for the next experiment and lastly gives the chance to perform the next experiment with similar pressure but less gas. 11. Using the 3 reference points, extrapolate your graph to ensure your absolute zero value is consistent with the known value of absolute zero. 12. Empty the dipper of any residual gas from the previous experiment and repeat steps 3 - 10 using Helium gas.

Observations: • When the gas tank is turned on and fills a container with a constant volume, the increase in pressure creates an increase in temperature, and more easily discovered the number of moles increases too • When the burner is lit, the temperature of the gas increases, as the volume is kept constant. The increase in temperature also causes an increase in pressure. This is all caused by the increase in kinetic energy given to the gas molecules from the release of energy from the combustion reaction happening in the burner. • When the gas molecules are released, there are less moles of the ideal gas in the container thus there is less pressure and the temperature decreases when the volume is kept constant. • If the jar volume is compressed there is an increase in pressure and temperature, the number of moles of ideal gas is kept constant Aw scale measurements to varying reference points

Reference Point Boiling Water Room Temperature

Temperature (Aw) 746.4 586

Reference Point

Temperature (Aw) 546.3

Ice Water

154

Boiling Nitrogen

0

Absolute 0

Results:

Reference Point

Temperature (Aw)

Boiling Water

746.4

373.2

586

293

546.3

273.15

154

73.15

0

0

Room Temperature Ice Water

Temperature (k)

Boiling Nitrogen Absolute 0

From this grid we can see Aw is double the value of Kelvin. Aw = 2K. Relative Pressure to Absolute Pressure

Reference Point Boiling Water

Relative Pressure (Torr)

Absolute Pressure (Torr) -217 1atm - reative pressure

=760- (-217) =977 Ice Water Boiling Nitrogen

42

718

551

209

*

Intercept X Variable 1

Standard Coefficients Error 9.418676683 0.421972 1.296567339 0.000779

Therefore, the pressure intercept is 9.4 +- 4x10^-1 and the slope is 1.3 +- 8x10^-4 The temperature intercept is where y = 0 0 = 1.296567339x + 9.418676683 - 9.418676683 = 1.296567339x X= -7.264317402 = -7.3

Used python Qexpy to calculate uncertainty import qexpy as q

m = q.Measurement(1.296567339,0.000779) b = q.Measurement(9.418676683, 0.421972) x = -b/m print(x) -7.3 +/- 0.3*

Conclusion: The pressure reaches zero at -7.2 +/- 3* 10 ^-1 Aw. This is fairly close to our known absolute zero showing that our newly defined temperature scale Awe is not perfect but an accurate temperature scale. The reason for this discrepancy could come from experimental error, we see that even with our uncertainty our value of “zero” is slightly higher than it should be. In theory Aw = 2K and the absolute zero value should be zero, but with any experiment data is not always analyzed or recorded perfectly. However, since our data is agreeable with theory, Aw is an accurate temperature scale, as well our data is accurate to 2 significant figures due to the pressure reading of ice water which gave us (42 torr). References:

Gregersen, E. (2020, September 10). Gas laws. Retrieved from https://www.britannica.com/science/gaslaws Jircitano, A. J. (n.d.). Retrieved from http://chemistry.bd.psu.edu/jircitano/gases.html Make Your Own Temperature Scale - Activity. (2020, July 13). Retrieved from https://www.teachengineering.org/activities/view/cub_energy2_lesson06_activity1...