Effect of temp. on rate constant - same for forward AND reverse rxn???

[CultureDoc]

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Hi guys,

From one of the TPR CBTs, they ask about the effect of increasing temperature on the rate of the forward rxn, the reverse rxn, and the eventual equilibrium for a particular rxn. This rxn is endothermic and rate = k[A].

I was good with the effect on the forward rxn and the equilibrium (as it's endothermic, heat would increase the rate of the forward rxn and hence shift equilibrium toward the products). What I did NOT get was the effect on the reverse rxn. I assumed it would be opposite of the forward rxn . . . but the explanation said "Increased temperature also increases the rate constant for both the forward and reverse reaction, which causes reaction rate to increase as well." I don't get why the effect on the reverse reaction is the same . . . can anyone explain it?

 

[engineeredout]

Arrhenius equation: k = Ae^-Ea/RT. That applies to both foward and reverse rxns. Increase T, increase k. Also shifts EQ but I think you know that.

 

[CultureDoc]

Increasing temperature shifts the equilibrium but alters both rates of reactions. LeChatlier's principals.

No, increasing temp does affect the rate - k values are temperature specific (and actually, in the passage it said that increasing the temp increased the rate by a certain amount per degree).

What I don't get is why it would supposedly have the same effect on the forward and reverse rxns. Is TPR just plain wrong on this one???

 

[CultureDoc]

Whoah . . . you changed your post . . . sorry!!

 

[engineeredout]

Whoah . . . you changed your post . . . sorry!!

Yeah cause after I typed it I was just like "Wait what the **** am I saying?"

Is it clear now?

 

[CultureDoc]

Arrhenius equation: k = Ae^-Ea/RT. That applies to both foward and reverse rxns. Increase T, increase k

Ok, good info . . . but I guess I still don't get why this applies to both the forward and reverse. Is that a rule of the Arrhenius eqn? Thanks . . . I feel like I'm losing it here!

 

[CultureDoc]

Bump.

Anyone?

 

[minhaj]

You are confusing thermodynamics with reaction kinematics. As the temperature increases so the KE of the molecules. Molecules moving at a faster rate with collide more frequently and reaction rate will increase in both directions. Temperature always speeds up a reaction both ways, regardless of the enthalpy change.

 

[CultureDoc]

You are confusing thermodynamics with reaction kinematics. As the temperature increases so the KE of the molecules. Molecules moving at a faster rate with collide more frequently and reaction rate will increase in both directions. Temperature always speeds up a reaction both ways, regardless of the enthalpy change.

Ok, yup - that makes sense. Thanks much! I'm discovering that this thermodynamics vs. kinetics issue is a common stumbling point for me. Must work on that!!

 

[minhaj]

Your welcome 🙂