http://www.ck12.org Chapter 19. Chemical Equilibrium
FIGURE 19.1
Berthollet was a chemist hired by Napoleon to travel to Egypt during what later became known as the Battle of the
Pyramids (1798). One day, Berthollet observed crystals of sodium carbonate (also known as trona) that had formed
along one of the ponds he was visiting.
FIGURE 19.2
Trona is a mineral composed of hydrated sodium carbonate, Na 2 CO 3 •10H 2 O, that is often found crystallized with
other salts. Berthollet was struck by this occurrence, because the double displacement reaction that often occurred
in the salt-rich natron ponds was expected to produce only calcium carbonate and sodium chloride, not sodium
carbonate.
Na 2 CO 3 (aq)+CaCl 2 (aq)→CaCO 3 (s)+2NaCl(aq)
Berthollet suggested that the presence of Na 2 CO 3 meant that this double displacement reaction was actually re-
versible.
Na 2 CO 3 (aq)+CaCl 2 (aq) CaCO 3 (s)+2NaCl(aq)
The reversibility of this reaction would explain how the reactants and products could all be present at the same time.