Nykoya Watson Chemistry August 31.2010 Lecture 2 Another Example from History—Why Do Some Things Burn? • Observations 1. Things would stop burning when placed in a closed container. 2. Many metals burn to form a white powder called calx. 3. Metals can be recovered from their calx by roasting it with charcoal. Why Do Some Things Burn? Phlogiston Theory • Explanation of combustion in early/mid-1700s. • Combustible substances contained a substance they called phlogiston . • When a substance burned it released all or some of its phlogiston into the air . How Does Phlogiston Theory Explain the Observations? • When a substance is burned in the open, all the phlogiston is released. • When a substance is burned in a closed container, the phlogiston is released until it saturates the container, at which point the combustion stops. • A metal’s calx is what is left after it releases all its phlogiston. • When roasted with charcoal the calx reacquires phlogiston from the charcoal.
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