Classy CAL On Chemicals

Chemical Collisions, from Cambridge Micro Software, manages to combine all the qualities you expect from a first-class CAL package (including the price - only £15.95).

The program, which comes on an 80-track disc, is aimed at 15 to 16 year-olds studying basic chemical changes, and at 17 to 18 year-olds working on the mathematics of reaction kinetics.

It shows the effects, at the molecular level, of combining two gases.

Each set of randomly-moving particles has its own colour, and if two particles of different colours collide with sufficient energy, a new white particle is formed. Simple in concept, the program does much more than this.

It not only takes into account elapsed time, temperature and initial molecular concentrations (all under user-control), but also continuously updates the data it is accessing, so that the chance of an effective collision is determined by an interaction of all three factors.

In addition, the element of randomness gives slightly differ ing results with each reaction. The result is that the program can be run several times using the same initial parameters, and the mean result calculated, just as in real experiments.

Numerical counts of all collisions, effective collisions only, and particle populations can be displayed at any time during a reaction, and plotted as graphs or bar charts to show how the relative particle con centrations have changed with time.

A reaction can be stopped at any point so that data can be analysed in detail.

User-definable controls allow colours of particles to be changed (essential with a mono chrome monitor), function keys to be used for storing sets of commands, and adjustments to be made to the monitor setting.

The quality of the graphics and speed of animation are well above average and the documentation is also very well done, with excellent teaching sugges tions.

Chemical Collisions has been designed throughout with the user in mind, and in operation it provides a flexible and very convincing simulation of chemical reactions and diffusions which no book or even video can hope to compete with.

Katherine Cranford