Idealvs. RealGases
56:Idealvs.RealGases
At roomtemperature and normalatmospheric pressures, real gases behave similarlyto ideal gases, but real gases candeviate significantlyfromideal gas behavior at extreme conditions such as high temperaturesand high pressures. It is not alwayseasy to find an effectivemeansto show the deviation fromideal gas behavior forreal gases. An effective but simplemethod to see these deviations is to
calculate the value of R, the ideal gas constant, for real gases assumingtheyfollow the ideal gas law and then comparethe value of Rwith the actual value of 0.08205 L atm K 1 mol 1. In this assignment,you
willmeasureP, V, T, and nfor various real gases under different conditions and thenyou willcalculate the value ofRand compare it with its actual value.
1. Start VirtualChemLaband select Ideal vs. Real Gasesfromthe listof assignments. The lab will open
in the Gases laboratorywith the balloonfilled with 0.100 moles of Ideal Gas 1.
2. Click on theUnitsbuttonsto change theunits to LormL for volume, atmfor pressure, and K for temperature. On the left of the gas chamber are LCDcontrollers for the volume, pressure, temperature, andmoles. On the left of the Pressure,Temperature, and Moles LCD controllers is a
lever that will decrease and increase thepressure, temperature, or moles as the lever ismoved upor down; the digit changes dependingonhow far the lever ismoved. Digitsmayalso be clicked directly
to type in thedesired number. Clicking to the left ofthe farthest left digit will add the next place; for example, if you have 1.7 atmyou can click left of the 1 and enter 2 to make it 21.7 atmor click left of the 2 and enter 5 tomake it 521.7 atm. The smallRbutton in the upper left corner rounds the number.
Clicking several timeswill round fromones to tens tohundreds.
The green arrow to the leftof theSavebutton will Zoom Out. Clicking ReturnTankon thegas cylinder will return the tank to the rackand allowyou to select a different gas. Clicking thegas
chamber willZoom Into allowyou tochange parameters. Be careful not to makethe balloon solarge that it bursts.If it does, click the red Resetbutton inthe top right and then reset your units and values
for each parameter. Remember that volumemust be in L. If mL appears, youmust convert to L in
your calculations.
3. Complete the data table forthe followinggases and conditions (allwith 0.100 mole):
a. Ideal gas at low T= 10 K, high T= 1000K, lowP= 1atm, highP= 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, lowP= 1 atm, highP= 15 atm
DataTable
Gas 
V(L) 
P(atm) 
T(K) 
n(mol) 
Ideal, low T, low P 

Ideal, low T,highP 

Ideal, high T,low P 

Ideal, high T,high P 

CH4, low T,low P 

CH4, low T,highP 

CH4, high T,low P 

CH4, high T,high P 
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Virtual ChemLab: General Chemistry, Student Lab Manual/Workbook, v4.5, Third Edition, by Brian F. Woodfield and Matthew C. Asplund. Published by Prentice Hall.
Copyright © 2006 by Pearson Education, Inc.
GasProperties
CO2, low T,low P 

CO2, low T,highP 

CO2, high T,low P 

CO2, high T,high P 
4. If PV= nRTthen R= PV/nT.
Complete the results table for each experiment above. Use four significant digits.
ResultsTable
Gas 
Calculated R(L atmK 1 mol 1) 
Ideal, low T,low P 

Ideal, low T,highP 

Ideal, high T,low P 

Ideal, high T,high P 

CH4, low T,low P 

CH4, low T,highP 

CH4, high T,low P 

CH4, high T,high P 

CO2, low T,low P 

CO2, low T,highP 

CO2, high T,low P 

CO2, high T,high P 
5. Which gases and conditions show significant deviation from the actual value of R?Explain.