SCIENCE PHOTO LIBRARY MOTION SCIENCE PHOTO LIBRARY MOTION
Sequence of clips showing the endothermic reaction between barium hydroxide and ammonium chloride. A beaker containing the two chemicals is set on a block of wood dampened with water. As the sequence starts, the chemicals are mixed with the probe of a digital thermometer and there is a dramatic drop in temperature from 22C to 5C. At 7 seconds the view moves to a top-down look into the beaker and the chemicals starting to form a slush. At 10 seconds we return to the thermometer that is now reading -5C. At 28 seconds we move to a wide shot of the experimental set up. The temperature has reached -19C. At 34 second, a technician lifts the beaker to show that the damp wooden block has frozen to it.
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