White Cliffs of Dover

At 25°C and 1 atm, this reaction does not occur. Witness the existence of the white cliffs of Dover and other limestone deposits over eons of time. However if the temperature is raised to about 1100 K, limestone decomposes to give off carbon dioxide gas at 1 atm. In other words, this endothermic reaction becomes spontaneous at high temperatures. This is true despite the fact that AH remains about 178 kj, nearly independent of temperature. 

THE WHITE CLIFFS OF DOVER CONSIST OF ALMOST PURE CALCIUM CARBONATE IN THE FORM OF CHALK. 

Deposits of fossil diatoms known as diatomaceous earth have been mined and used for years in paints, abrasives, and other products such as chalk. The famous White Cliffs of Dover in England (rising to 300 feet) are composed of massive amounts of diatoms— coccoliths—that were laid down some 790 million years ago when Great Britain was submerged by a shallow sea. 

The White Cliffs of Dover, England, are composed mainly of calcium carbonate (CaCOj). 

Rule 6 addresses compounds that contain the carbonate ion— CO3. Some of the most common minerals in nature are various forms of calcium carbonate (CaCOj) and include calcite, Umestone, aragonite, travertine, chalk, and marble, all of which are white in color. Some limestone consists of very large formations that are now exposed to view. The famed white cliffs of Dover, England a large layer of the Grand Canyon in Arizona and an exposed layer of limestone in the Guadalupe Mountains of Texas, which date from the Permian Era, are all made of calcium carbonate. 

However, the reverse reaction is thermodynamically more favourable. If calcium chloride and sodium carbonate are mixed, sodium chloride and calcium carbonate are immediately formed — this is fortunate as otherwise the White Cliffs of Dover would have dissolved into the salt water of the English Channel long ago ... 

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