Exploding Rock

The white rock cracks into small pieces when it is soaked with water.

Scientific name: Calcium oxide reacts with water with release of a large amount of heat.


Free Range Chemistry 27 - Exploding Rock

by Royal Society Of Chemistry

CaO + H2O Calcium oxide and water תחמוצת סידן ומים

by davidsonweb

how to make calcium hydroxide

by The Thought Emporium


Wear eye protection goggles and gloves. Use safety screen for demonstration.

Always follow general safety recommendations. Please note that conducting chemistry experiments you must comply with the relevant legal procedures in your country.

Reaction formula

CaCO3 -[T]→ CaO + CO2

CaO + H2O → Ca(OH)2

Step-by-step instruction

  1. Put a piece of solid calcium oxide into the beaker. Calcium oxide could be obtained by heating of calcium carbonate or calcium carbonate containing materials such as limestone or seashells.
  2. For a more impressive (but more dangerous!) demonstration take a large piece of calcium oxide the size of a rock. Put it into a tray and cover with a safety screen.
  3. Pour some water on calcium oxide surface.
  4. Steam is generated. Calcium oxide reacts with water so vigorously that our rock explodes.

Scientific background

Calcium oxide (or quicklime) is a white solid substance. If it is pressed in a large piece it looks like a rock. It could be obtained by thermal decomposition of calcium carbonate. Heating calcium carbonate it is possible to drive out carbon dioxide leaving behind calcium oxide. Chemical properties of quicklime are typical for basic oxides. It reacts with water vigorously producing calcium hydroxide. This reaction is very exothermic. The released heat is causing the rock to crack in smaller pieces. The steam is produced by the excess of water which evaporates under increasing temperature.


Published on 25 June 2015

  • Fire
  • Heating with fire
  • Explosion
  • Poisoned gas
  • Organic
  • Electricity
  • Solution
  • Oxidation reduction
  • Color change
  • Precipitate
  • Gassing
  • Catalyst