Details

The final concentrations (green line for products, black line for reactants) have to be positive, but the value of can be negative. There are three cases:

Snapshot 1:

The position of the equilibrium is shifted to the right; the initial concentrations of the reactants and decrease, while the initial concentration of the product increases.

Snapshot 2:

The reaction has already achieved the equilibrium status; macroscopically the initial concentrations of the reactants and the initial concentration of the product do not change.

Snapshot 3:

The position of the equilibrium is shifted to the left; the initial concentrations of the reactants increase, while the initial concentration of the product decreases.

The colored window represents the variation of during the reaction because, as and are colorless, the gaseous solution develops a reddish color depending on the concentration of , a typical color of this gas.

The marks and are guidelines to help assess the changes generated by the experimental conditions. Mark moves along the time axis (as in the first two plots), while mark is connected with the concentration axis of the first plot.

References

[1] G. Follo, S. Z. Lavagnino, and G. Valorio, "Scuola secondaria superiore (biennio): L'applicazione di DERIVE 5 alle tematiche inerenti l'equilibrio chimico," La Chimica nella Scuola, Rome: Aracne, 2015, pp. 31–44. www.aracneeditrice.it/pdf/9788854884328.pdf.

[2] D. A. McQuarrie and J. D. Simon, Chimica Fisica: Un approccio molecolare, Bologna: Zanichelli, 2000.