Rates of Yellow

A reaction between two white solids occurs when lead nitrate and potassium iodide are shaken forcefully producing a mixture of yellow and white solid products. The reaction occurs almost instantaneously when aqueous solutions of these compounds are mixed, precipitating yellow lead iodide.

Pb(NO3)2 + 2KI → PbI2 + 2KNO3

Thermite

thermite, cannon balls

As two rusty cannon balls (one covered in aluminum foil) are smashed together, sparks and a cracking sound are produced.
Fe2O3 (s) + 2Al (s) → Al2O3 (s) + 2Fe (s)