# Rescale Reactions

A non-spatial ODE model contains reaction rates that specify
a rate of change of species **total amount** in a given compartment.

In a PDE model, we have

compartment reactions: rate of change of species

**concentration**membrane reactions: rate of species

**amount crossing unit area**of the membrane

The last step in importing a non-spatial model is to rescale the reactions appropriately, by clicking on “rescale reactions” in the bottom right of the window.

This opens a guided workflow that automatically rescales the image depth and the reaction rate expressions, with the goal of constructing a valid PDE model that initially reproduces the behaviour of the imported ODE model, in the following limit of the spatial model:

no initial spatial dependence of species concentrations

infinitely fast diffusion

consistent compartment volumes between ODE model and PDE model geometry