SCIENCE PHOTO LIBRARY SCIENCE PHOTO LIBRARY
Sequence of shots showing an endothermic reaction. At left solid barium hydroxide and solid ammonium chloride have been place in a flask that is sitting on a damp piece of wood. The digital thermometer shows the temperature in the flask to be 21 degrees Celsius. As the two chemicals are mixed an endothermic, or heat-absorbing, reaction takes place and the temperature inside the beaker drops dramatically. This drop in temperature freezes the water between the flask and wooden block, sticking the two together (right).
Model release not required. Property release not required.