5-3: Avogadro’s Law: Moles and Volume
In 1808, Joseph Gay-Lussac observed the law of combining values, which states that the volumes of gases that react with one another react in the ratio of small whole numbers. Three years later, Amedeo
Avogadro built upon this observation by proposing what is now known as Avogadro’s hypothesis: Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules. Avogadro’s Law, which states the relationship between moles and volume, followed from his hypothesis. You will be observing the same principle that Avogadro stated two hundred years ago.
- Start Virtual ChemLab, select Gas Properties, and then select Avogadro’s Law: Moles and Volume from the list of assignments. The lab will open in the Gases laboratory.
- Note that the balloon in the chamber is filled with 0.100 moles of an ideal gas (MW = 4 g/mol) at a temperature of 298.00 C, a pressure of 2.000 atm. To the left of the Number of Moels LCD controller is a lever that will decrease and increase the number of moles of gas as it is moved up or down; the digit changes depending on how far the lever is moved up or down. Digits may also be clicked directly to type in the desired number, or they can be rounded by clicking on the R button. You may want to practice adjusting the lever so that you can decrease and increase the number of moles of gas accurately. Make sure the moles, temperature, and pressure are returned to their original values before proceeding.
- Click on the tenths digit on the Moles LCD controller and change the moles of gas in the balloon from 0.100 to 0.050 mole. Record the volume, pressure, temperature and number of moles in the data table below.
Increase the number of moles of gas from 0.050 to 0.500 moles in 0.050 mole increments (0.050, 0.100, 0.150 etc). After each increment, record the volume, pressure, temperature and number of moles in the data table below.
Data Table: Ideal Gas (MW = 4 g/mol)
|V (L)||P (atm)||T (C)||Number of moles (n)|
- Open the MS-Excel file “Avogadros_Law_Plot_Ideal_Gas”. Enter your data into the data table spaces in the Excel file as appropriate. It will automatically generate a graph of Volume (L) vs Number of Moles (n). The graph will feature a best-fit straight line with an equation and quality of fit (R value). Save this file for submission along with this worksheet.
- Based on your graph, qualitatively describe the relationship between the volume and number of moles of a gas (assuming a constant pressure and temperature).
- An 8.7 L sample containing 0.34 mol of NO2 gas is completely converted to N2O4 according to the reaction shown below, while maintaining the same temperature and pressure. What is the volume of N2O4 gas after the conversion?
2 NO2(g) → N2O4(g)