What Happens to an Exothermic Reaction if the Temperature Is Increased?
An exothermic reaction generates heat. Unless the reaction is cooled in some way, its temperature increases. If you increase the temperature with an external heater, it slows the reaction down or reverse its direction. Note that this is true if the reaction is in equilibrium. If not, heating the reaction may increase its rate.
Le Chatelier’s Principle
A chemical reaction in equilibrium is one that has arrived at a steady state. Although molecules continue to react, no net change occurs in the concentrations of products and reactants. According to Le Chatelier’s Principle, if you oversupply one of the products of a reaction in equilibrium, it will slow or reverse direction, producing reactants and consuming products. Since heat is a product of an exothermic reaction, adding more of it reduces the reaction rate or causes it to change direction.
Arrhenius Equation and Thermal Runaway
A reaction that’s not in equilibrium continues to consume reactants and produce products. A chemical relationship called the Arrhenius equation describes temperature’s role in the rate of a reaction: a cooler temperature slows a reaction down, and a higher temperature speeds it up. An endothermic reaction that’s just beginning proceeds faster at warmer temperatures. If the temperature is too high, heat may build up in the reactants, leading to a dangerous thermal runaway. In that case, the reaction gathers speed until it explodes.
Chicago native John Papiewski has a physics degree and has been writing since 1991. He has contributed to "Foresight Update," a nanotechnology newsletter from the Foresight Institute. He also contributed to the book, "Nanotechnology: Molecular Speculations on Global Abundance."