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In chemistry, exothermic reactions are those that release heat into their surroundings. When the temperature of such a system is raised, two primary effects occur: the reaction rate accelerates, and the position of chemical equilibrium can shift.
Higher temperatures generally speed up exothermic reactions, but they can also move the equilibrium toward reactants, limiting the final yield.
Across the board, temperature boosts reaction speed. This is because the Arrhenius equation shows that the rate constant k increases exponentially as temperature rises: k = A e^(–Ea/RT). For example, a match ignites almost instantaneously when its tip is struck, whereas at room temperature the same chemical mixture remains inert for hours.
Most chemical processes are reversible. As reactants convert to products, the forward reaction slows while the reverse reaction gains momentum. When the rates balance, the system reaches equilibrium: the concentrations of reactants and products no longer change. The equilibrium composition depends on the specific reaction.
Le Chatelier’s principle predicts how a system at equilibrium responds to external changes. Adding more products pushes the reaction back toward reactants; adding reactants drives it forward. This principle is fundamental for understanding industrial processes and laboratory manipulations.
For exothermic reactions, heat is a product. Raising the temperature effectively introduces additional product (heat), prompting the system to favor reactants to re‑establish equilibrium. Consequently, the higher the temperature, the greater the shift toward reactants. A classic illustration is the Haber process (N₂ + 3H₂ ⇌ 2NH₃). At low temperatures, ammonia formation is slow; increasing the temperature accelerates the kinetics but simultaneously drives the equilibrium back toward nitrogen and hydrogen, reducing ammonia yield.
In summary, while heating an exothermic reaction can accelerate its progress, it often sacrifices product yield by moving the equilibrium toward reactants. Engineers and chemists must balance temperature to optimize both rate and yield.
