Why is the hypochlorination reaction of phosphorus trichloride carried out by first cooling and then heating?
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Yellow phosphorus reacts with chlorine to form phosphorus trichloride, and phosphorus trichloride reacting with chlorine to form phosphorus pentachloride are both exothermic reactions. But why, in production, when there is an excess of chlorine in phosphorus trichloride, is it necessary to cool first and then heat up, rather than heating up directly?
The phosphorus pentachloride produced can be decomposed into phosphorus trichloride; generally, about 40% of the phosphorus pentachloride undergoes decomposition
Are you saying that the decomposition of phosphorus pentachloride is endothermic? However, the reduction reaction between phosphorus pentachloride and yellow phosphorus releases a large amount of heat
This is because the heat released when yellow phosphorus reacts with phosphorus pentachloride is greater than the heat released when yellow phosphorus reacts with chlorine, which in turn is greater than the heat released when chlorine reacts with phosphorus trichloride.