SPANA: Modify a Chemical System

A chemical system may be modified by selecting either one of the pull-down menus: “File / Data File / Modify” and “Run / Modify Chemical System”. A new window appears showing the chemical system. The reaction and the equilibrium constant are shown in a status bar when you point with the mouse to a species name in the lists:

Delete
Exchange a component with a reaction
Merge with another data file
Deactivate a species or change its logK

			Delete either a single reaction or a component, with all reactions where it participates. For example, removing the component Cu²⁺ will also take away CuOH⁺, etc.

			Exchange a component with a reaction. For example: Fe²⁺ for Fe³⁺; CO₂(g) for CO₃²⁻; etc. This is useful when the equilibrium constants are based on CO₃²⁻ as a component but a diagram for a given CO₂(g) partial pressure is needed (example). May also be used to create diagrams for solutions saturated with a solid (example with Al).

			Merge with another data file (Only in advanced program level). For example: merge a file with the components H⁺, e−, Fe²⁺ and a file with Cr³⁺, e−, H⁺, to create a file with the system: H⁺, e−, Fe²⁺, Cr³⁺. Note that afterwards you will need to add manually any species formed by both Fe and Cr, for example FeCr₂O₄(s).

By double-clicking on a reaction product a new window appears where you can easily deactivate the species (by adding a “*” at the beginning of the name) and/or change the equilibrium constant:

This window allows you to make changes quickly without the need of a text editor and without learning the format of the input data file. Note, however, that components can not be deactivated with SPANA; you must use a text editor to add a “*” at the start of their names. However, it is always possible to first deactivate a species and then exange it with a component.