[Catalist] Equilibrium and temperature

[Brendan Selby]

The dependence of the rate constant for a chemical reaction is given be the Arrhenius Equation k = A exp(-Ea/(RT)) where Ea is the activation energy.

The Ea will always be larger for the endothermic reaction since Ea(endo) = Ea(exo) + the magnitude of delta H. This can easily be seen in the energy profile diagram.

Since Ea is larger for the endo reaction, increasing T has a bigger effect on the power in the exponent. Hence a bigger effect on the rate constant.

This effect on the rate constant will always mean a greater rate if all concentrations are unchanged regardless of the order of the reaction.



Sent on the go with Vodafone


-------- Original message --------
From: Andrew Bland <abl at gmas.wa.edu.au>
Date: 24/11/17 12:15 pm (GMT+08:00)
To: Catalist at lists.stawa.net
Subject: [Catalist] Equilibrium and temperature

Dear chemistry teachers,

When a system is heated, both the forward and reverse reaction rates increase, “but the endothermic reaction increases more than the exothermic reaction. The endothermic reaction is always affected more by a temperature change than the exothermic reaction. This is true even when a system is cooled…” Chem for WA 2.

My question is why is the endothermic reaction rate always effected more than the exothermic rate? I cannot find an explanation in any of my texts, only a re-stating of this in various forms.

Thanks

Andrew




Andrew Bland
Head of Year 10 and Head of Geographe House

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