Enthalpy vs. Entropy Graphing Tool

This tool is designed to help you understand the effects of reaction enthalpy (DH°rxn) and entropy (DS°rxn) changes and temperature on the standard state Gibbs free energy change (DG°rxn). In the "Qualitative" version, which appears first, gauges fill in the positive and negative directions for DS° and DH° as the plot is adjusted.

Favorable parameters for a spontaneous reaction are indicated by the color green and non-favorable parameters are shown in red. If you are having trouble understanding the graphing tool, the questions below are designed to help you sort out the variables.

Instructions for using the Graphing Tool

Table of Thermodynamic Data

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Observe what happens to the DH° and DS° indicators when you leave the y-intercept the same and use the endpoint of the line to adjust the slope.

What happens if you move the y-intercept instead?

Think about what is represented by the :


Can you find a favorable reaction temperature when DH° is positive? What sign is DS°?

When both DS° and DH° are negative, what temperatures (high or low) favor the reaction?


Click on the endpoints of the graph to move the line and change DH°rxn and DS°rxn. Use the + and - to change the temperature scale. The "Qualitative" and "Quantitative" buttons switch back and forth between two versions of the tool. The gauges in the "Qualitative" version only show up to 200 J/mol-K for DS° and 500 kJ/mol-K for DH°. If you want to see values above (or below for negatives) those, you need to switch to the "Quantitative" version. The "Quantitative" version allows you to type values for DH°rxn and DS°rxn into input boxes. Because of computer screen limitations, these values will change slightly once you hit enter or click in the graph area to input the data.

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