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Why does increasing the reaction temperature favor the endothermic but not exothermic reaction?

Increasing the reaction temperature will increase the molecular movement no matter reactants for exothermic and endothermic reactions. And the second argument is compare to endothermic reaction, exothermic reaction always have a lower activation energy, so when we increase the temperature (energy), seems exothermic reaction is more readily to activated and it seems that it should have a higher reaction rate.

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    $\begingroup$ You're mixing kinetics and thermodynamics. In general, reactions go faster in higher temp. but position of equilibrium can shift towards substrates nonetheless. $\endgroup$
    – Mithoron
    Commented May 25 at 14:55
  • $\begingroup$ Increasing temperature accelerates the endothermic reaction direction more than the exothermic one. See also van't Hoff equation $\endgroup$
    – Poutnik
    Commented May 25 at 14:55

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At equilibrium the rate of forwards and backwards reaction are equal, but the rate constants will generally not be. If the temperature is increased both of the rate constants will increase as there is more energy and so more molecules have the ability to react. Both forward and backward reactions are affected but not equally because their activation energies are different. A new equilibrium is now reached and the rates are again equal. The van't Hoff equation describes what happens to the equilibrium constant for exo- and endo- thermic reactions. For an exothermic reaction $K_p$ decreases as the temperature increases, and for an endothermic reaction $K_p$ increases with increasing temperature.

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