September 8 - 15, 2005
Objectives. The primary objective of this lab is the experimental determination of the heat capacity ratio (Cp/Cv) for two gases, He and N2. The measurement will be carried out using two different experimental techniques.
| Adiabatic Expansion. |
| Sound Velocity Method. |
Logistics. This is a two-part lab that will be conducted during the September 9th and 16th laboratory periods. Students should work in three groups of two students each. Two Kundt's tubes will be available for student use as will the equipment necessary to perform an adiabatic expansion experiment.
Background information and procedures are available from the following textbooks that will be available the morning prior to lab:
| Garland, Nibler, and Shoemaker "Experimental Physical Chemistry", page 104. |
| Sime "Physical Chemistry: Methods, Techniques, and Experiments", Page 408. |
Information regarding this lab are also available at a number of websites.
Report Information
Introduction. Provide a brief background for each technique used in this experiment. Exhaustive derivations are not required but the expressions used to determine the heat capacity ratio from the experiment should be provided.
Data analysis. The Shoemaker text provides an invaluable reference for analyzing the data of this experiment. Your lab report should include the following:
| Calculate the heat capacity ratio (Cp/Cv) for each of the gases analyzed (He and N2) using both the adiabatic expansion method and the sound velocity method. The data should be tabulated with average values and uncertainties reported. |
| Use the obtained Cp/Cv ratios and the relationship Cp=Cv+R to calculate Cp and Cv values for each gas. |
| Compute a theoretical value of Cv for each gas. For N2, compute Cv both with and without the vibrational contribution. |
Discussion questions.
| How do the experimental heat capacities compare with the accepted theoretical results? |
| Which technique provides a more accurate value for the heat capacities? |
| Which technique provides a more precise value for the heat capacities? |