Vernier Software and Technology
Vernier Software & Technology

Investigating Thermodynamic Relationships of Substituted Hydrocarbons


There are multiple ways to measure the change in thermodynamic parameters (i.e., Gibb’s free energy, ΔG; enthalpy, ΔH; and entropy, ΔS) during a chemical reaction. Gas chromatography provides one methodology for determining these values because the retention times reported are a result of a reaction between the mobile phase running through the column and the stationary phase that resides on the column. Here, you will measure the equilibrium constant experienced between the mobile and stationary phases which will allow you to isolate the ΔG, ΔH, ΔS of the reaction.

The equilibrium constant is referred to as the distribution coefficient, Kc, and it can be expressed in terms of the capacity factor, k′

Kc = k′β

where β is the column phase ratio, a quantity typically given by the manufacturer. The Vernier Mini GC has a column phase ratio value of approximately 200.

Once the equilibrium constant (or distribution coefficient) is known, it is possible to determine various thermodynamic quantities. The standard Gibb’s free energy change involved in the mobile phase-stationary phase transition is calculated by:

ΔG°= –RT ln(Kc)

By analyzing the retention time at more than one temperature, the enthalpy and entropy changes involved in the process can also be found.



In this experiment, you will

  • Collect and analyze GC data from various samples.
  • Calculate the equilibrium constant between the various compounds and the GC column.
  • Use the equilibrium constant to identify the change in free energy of solution.
  • From the temperature dependent data, calculate the change in enthalpy and entropy of the solution.
  • Observe the changes in Gibb’s free energy with the number of carbon atoms in the samples studied.

Sensors and Equipment

This experiment features the following Vernier sensors and equipment.

Additional Requirements

You may also need an interface and software for data collection. What do I need for data collection?

Organic Chemistry with Vernier

See other experiments from the lab book.

1Determining Melting Temperature
3Determination of a Boiling Point
4Identifying an Unknown Analgesic by Three Methods
5Separation of Organic Compounds by Acid-Base Extraction Techniques
6Understanding Polarimetry
7Identification of Organic Unknowns Using Polarimetry
8Investigating Gas Chromatography
9Fractional Distillation of Esters
10Understanding Intermolecular Forces Using a Gas Chromatograph: Enthalpy of Vaporization
11Investigating Thermodynamic Relationships of Substituted Hydrocarbons
12Extraction of Spinach Pigments and Analysis by Electronic Absorption Spectroscopy
13SN1: Synthesis of t-butyl chloride
14SN2: Synthesis of 1-bromobutane
15Observing the Reaction Kinetics of Sucrose with Polarimetry
16The Synthesis and Analysis of Aspirin
17Isolation of R-(+)-Limonene from Oranges using Steam Distillation
18Synthesizing Ethyl Acetate by Fisher Esterification
19Synthesis of Dibenzalacetone by Aldol Condensation
20The Diels-Alder Reaction of Anthracene with Maleic Anhydride
21Friedel-Crafts Acylation of Ferrocene
22Grignard Formation of Crystal Violet
23Synthesis of Fluorescein
24Synthesis of Methyl Orange and Its Application to Textiles
25Analysis of Natural Products
26Using a Gas Chromatograph: Identifying an Unknown Compound

Experiment 11 from Organic Chemistry with Vernier Lab Book

<i>Organic Chemistry with Vernier</i> book cover

Included in the Lab Book

Vernier lab books include word-processing files of the student instructions, essential teacher information, suggested answers, sample data and graphs, and more.

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