The first set of beakers contains varying amounts of solution A and water. The second set of beakers contains varying amounts of solution B and water. One set has green indicator, the other red.
The clock reaction shown proceeds in a linear fasion. The beakers on the left change first while the beakers on the right change last.
The beakers change color at different rates because of the different concentrations of starting materials, particularly the materials involved in the rate-limiting step, the production of formaldehyde:
CH2(OH)2 --> HCHO + H2O
The faster the formaldehyde is produced, the faster the beakers change color.
An NSF funded Project