Ideal vs. Real Gases

Ideal vs. Real Gases

Ideal vs. Real Gases

At room temperature and normal atmospheric pressures, real gases behave similarly to ideal gases, but real gases can deviate significantly from ideal gas behavior at extreme conditions such as high temperatures and high pressures. It is not always easy to find an effective means to show the deviation from ideal gas behavior for real gases. An effective but simple method to see these deviations is to calculate the value of R, the ideal gas constant, for real gases assuming they follow the ideal gas law and then compare the value of R with the actual value of 0.08205 LatmK-1mol-1. In this assignment, you will measure P, V, T, and n for various real gases under different conditions and then you will calculate the value of R and compare it with its actual value.

1. Start Virtual ChemLab and select Ideal vs. Real Gases from the list of assignments. The lab will open in the Gases laboratory with the balloon filled with 0.100 moles of Ideal Gas 1.

2. Click on the Units buttons to change the units to L or mL for volume, atm for pressure, and K for temperature. On the left of the gas chamber are LCD controllers for the volume, pressure, temperature, and moles. On the left of the Pressure, Temperature, and Moles LCD controllers is a lever that will decrease and increase the pressure, temperature, or moles as the lever is moved up or down; the digit changes depending on how far the lever is moved. Digits may also be clicked directly to type in the desired number. Clicking to the left of the farthest left digit will add the next place; for example, if you have 1.7 atm you can click left of the 1 and enter 2 to make it 21.7 atm or click left of the 2 and enter 5 to make it 521.7 atm. The small R button in the upper left corner rounds the number. Clicking several times will round from ones to tens to hundreds.

The green arrow to the left of the Save button will Zoom Out. Clicking Return Tank on the gas cylinder will return the tank to the rack and allow you to select a different gas. Clicking the gas chamber will Zoom In to allow you to change parameters. Be careful not to make the balloon so large that it bursts. If it does, click the red Reset button in the top right and then reset your units and values for each parameter. Remember that volume must be in L. If mL appears, you must convert to L in your calculations.

3. Complete the data table for the following gases and conditions (all with 0.100 mole):

a. Ideal gas at low T = 10 K, high T = 1000 K, low P = 1 atm, high P = 15 atm b. Methane gas (CH4) at low T = 160 K, high T = 400 K, low P = 1 atm, high P = 15 atm c. Carbon dioxide gas (CO2) at low T = 250 K, high T = 1000 K, low P = 1 atm, high P = 15 atm

Data Table Gas

Ideal, low T, low P Ideal, low T, high P Ideal, high T, low P Ideal, high T, high P CH4, low T, low P CH4, low T, high P CH4, high T, low P CH4, high T, high P

V (L)

P (atm)

T (K)

n (mol)

CO2, low T, low P CO2, low T, high P CO2, high T, low P CO2, high T, high P

4. If PV = nRT then R = PV/nT.

Complete the results table for each experiment above. Use four significant digits.

Results Table Gas

Ideal, low T, low P Ideal, low T, high P Ideal, high T, low P Ideal, high T, high P CH4, low T, low P CH4, low T, high P CH4, high T, low P CH4, high T, high P CO2, low T, low P CO2, low T, high P CO2, high T, low P CO2, high T, high P

Calculated R (LatmK-1mol-1)

5. Which gases and conditions show significant deviation from the actual value of R? Explain.

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