UTF-8Avogadro's law: The V-n relationship at constant temperature and pressureGas Laws: Avogadro's Law
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Our final gas law is known as Avogadro's law. Here we'll discover the relationship that exists between the moles and volume of a gas (at constant temperature and pressure).
Before we start, remember that if we say we are increasing the number of molecules of gas, it means the same as saying we are increasing the number of moles of gas (or if we say we are decreasing the number of molecules of gas, it means the same as saying we are decreasing the number of moles of gas). If you need a review on what a mole is, click here.
We'll do this experiment a little differently than the ones we did for the other three gas laws. This time we'll ask you to run a series of experiments, one right after another, each time changing the number of molecules of gas and observing how the volume is effected. Some details about our simulator:
The simulator currently contains 120 molecules. The piston is not in a fixed position; it can expand or contract so as to maintain a constant pressure.
The small triangle on the right side of the bar graph (it will appear immediately after starting the simulator) records the average volume over the last 20,000 fs. For all six experiments, stop the simulator when the level of this triangle stays relatively constant (wait at least 60,000 fs each time; the clock is in the lower left hand corner of the simulator).
Since we are using a two-dimensional model, what we are calling "volume" on the bar graph below is really the length the piston moves from the wall (in angstroms).
Instructions:
1. Click Run. Observe any changes in the volume of the container. Click Stop when the small triangle on the bar graph stays relatively constant.
2. Record the average volume of the container (the level of the triangle) by writing it in the "120 molecules" box below.
volume (length in angstroms)
3. Select the "100 molecules" button.
4. Click Run and again observe any changes in volume. Stop the simulation when the volume stays relatively constant (remember, wait at least 60,000 fs).
5. Record the volume of the 100 molecule container by writing the value in the appropriate box.
6. Repeat Steps 3-5 for the remaining four buttons.
As we decreased the number of moles of gas, we discovered that the volume decreased because the gas molecules collided with the walls of the container with less frequency. In other words, the piston responded to the fewer collisions by decreasing the size of the container until the pressure was brought back to its original level (i.e. until the frequency of collisions reached its original level).
This direct relationship between moles and volume is known as Avogadro's law.
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130.030.015true130.030.0130.030.01111page5.cml1111index.cml1111page7.cml11130.030.030.030.0true30.030.030.030.0truetruetruetruemole.cml30.030.030.030.030.030.030.030.030.030.030.030.030.030.0true30.030.030.030.030.030.030.030.0true30.030.030.030.030.030.030.030.0org.concord.mw2d.activity.AtomContainerpage6$0.mmlfalsefalseorg.concord.modeler.PageBarGraphX: Obstacle #0volume (length in angstroms)0.102100250true840true-66330100.040.023.23717838581171730.030.030.030.0org.concord.modeler.PageButtonRunorg.concord.mw2d.models.MolecularModel0Execute MW scriptorg.concord.modeler.PageButtonStoporg.concord.mw2d.models.MolecularModel0Execute MW script30.030.030.030.0org.concord.modeler.PageRadioButton120 moleculesPuts 120 molecules total in the containertruetrueorg.concord.mw2d.models.MolecularModel01138816545877Execute MW scriptorg.concord.modeler.PageRadioButton100 moleculesPuts 100 molecules total in the containertrueorg.concord.mw2d.models.MolecularModel01138816545877Execute MW scriptorg.concord.modeler.PageRadioButton80 moleculesPuts 80 molecules total in the containertrueorg.concord.mw2d.models.MolecularModel01138816545877Execute MW scriptorg.concord.modeler.PageRadioButton60 moleculesPuts 60 molecules total in the containertrueorg.concord.mw2d.models.MolecularModel01138816545877Execute MW scriptorg.concord.modeler.PageRadioButton40 moleculesPuts 40 molecules total in the containertrueorg.concord.mw2d.models.MolecularModel01138816545877Execute MW scriptorg.concord.modeler.PageRadioButton20 moleculesPuts 20 molecules total in the containertrueorg.concord.mw2d.models.MolecularModel01138816545877Execute MW script30.030.030.030.0true30.030.01130.030.014trueorg.concord.modeler.PageTextField10<html>
120 molecules
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100 molecules
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80 molecules
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60 molecules
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40 molecules
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20 molecules
</html>30.030.030.030.030.030.030.030.030.030.030.030.030.030.0org.concord.modeler.ImageQuestion540550Line<html><font size = 3 face = Verdana>Which of the five graphs below represents the relationship between the moles and volume of a gas at constant pressure and temperature (volume increases from top to bottom on y-axis and moles increases from left to right on x-axis)?</font></html>30.030.030.030.030.030.0org.concord.modeler.PageMultipleChoicetrue3370140<html>
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<font size="3" face="verdana">As the moles decreased, what happened to the
volume?</font>
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truevolume increasedvolume decreasedvolume remained the same1 falseLineorg.concord.modeler.PageMultipleChoicetrue3550140<html>
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<font size="3" face="verdana">Which of the following best explains what
occurred as the number of moles were decreased?</font>
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truethe force of the collisions with the walls of the container decreased, therefore the volume decreasedthe frequency of the collisions with the walls of the container decreased, therefore the volume decreasedboth "a" and "b"1 falseLine30.030.030.030.0true30.030.0true30.030.0org.concord.modeler.PageMultipleChoicetrue2400140<html>
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<font size="3" face="verdana">The relationship between the moles and
volume of a gas (at constant temperature and pressure) can be best
described as:</font>
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truedirectly proportionalinversely proportional0 falseLine30.030.030.030.0true30.030.030.030.030.030.030.030.011130.030.01111page5.cml1111index.cml1111page7.cml1111