Chemical Concepts Demonstrated: Temperature's effect on reactions, heat catalysis
The beakers all change color from pink to green when the CoCl2 is added. The solutions turn pink again, but at different times. Typically, the beaker at 25o C changes in 10 minutes, the beaker at 45o C changes in 3 minutes, the beaker at 55o C changes in 1 minute, and the beaker at 65o C quickly flashes through the colors.
Heat itself makes a fairly good catalyst in certain cases. This demonstration can show this fact quite well.
CoCl2, in the presence of water, forms Co(H2O)62+, which is pink. In the presence of both H2O2 and tartrate ion, a green cobalt-tartrate-peroxide complex is formed, which can formally be assumed to contain Co(III). With time, the Co(III) oxidizes one of the tartrate ligands to CO2 and is itself reduced to Co2+; at this point, the pink color of the solution returns. The rate at which the pink color returns depends on the temperature.