Changing Temperature in equilbrium reactions

[Dr. To Be]

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Good morning all,

I am having a issue with grasping this concept. I just want to make sure I am understanding it correctly.

In equilibrium reactions,

Increasing Temp: Shifts Reaction to the Left(Reverse Reaction) to consume extra heat and make more of Reactants.
---> Making this an endothermic Reaction?

Decreasing Temp: Shifts reaction to the right (forward reaction) to produce extra heat and make more products
----> Making this an exothermic reaction?

Is this correct?

Thanks!

 

[Quinoline]

You are correct, I believe.
You can think that the system will react to minimize the external stress, so increasing temp will cause the system to try to decrease the temp.

Or you can think that an exothermic reaction requires less heat energy to move in the forward direction than the reverse direction (the distance from reactants to peak is less than the distance from products to peak). So if you decrease the temperature, you will have less heat so the reverse reaction will be more difficult to happen since it requires more heat energy, so the reaction will go forward in the exothermic direction.

 

[Dr. To Be]

Thank you so much!

 

[Labrat07]

I think this is incorrect. Please let me know otherwise.

When I look at this, I'm think of le chatlier principle.

in exothermic reaction, ( reaction releasing heat ) A +B = C + HEAT
-adding heat = move the reaction to the left
-removing heat = move the reaction to the right

in endorthermic reaction ( Gaining heat) A+ HEAT = B + C
- adding heat = move to the left
- removing heat = move to the right

Ref just in case, http://www.chemteam.info/Equilibrium/Keq-Effect-of-temperature.html

 

[amy_k]

Good morning all,

I am having a issue with grasping this concept. I just want to make sure I am understanding it correctly.

In equilibrium reactions,

Increasing Temp: Shifts Reaction to the Left(Reverse Reaction) to consume extra heat and make more of Reactants.
---> Making this an endothermic Reaction?

Decreasing Temp: Shifts reaction to the right (forward reaction) to produce extra heat and make more products
----> Making this an exothermic reaction?

Is this correct?

Thanks!

I'm not sure if you are saying increasing temperature for an equilibrium reaction shifts the equilibrium to the endothermic direction (if we started with an exothermic reaction this would be the reverse direction).

Whereas decreasing temperature shifts the equilibrium to the exothermic direction.

Is this what OP meant?

 

[Quinoline]

Increasing Temp: Shifts Reaction to the Left(Reverse Reaction) to consume extra heat and make more of Reactants.
---> Making this an endothermic Reaction?

in endorthermic reaction ( Gaining heat) A+ HEAT = B + C
- adding heat = move to the left

------------------------------------------------------------------------------------------------------------------

Decreasing Temp: Shifts reaction to the right (forward reaction) to produce extra heat and make more products
----> Making this an exothermic reaction?

in exothermic reaction, ( reaction releasing heat ) A +B = C + HEAT
-removing heat = move the reaction to the right

Where is the discrepancy?

 

[amy_k]

i think it is just unclear whether OP is saying "in an endothermic reaction, increasing temp shifts reaction to the left to consume extra heat and make more reactants" or if they are using the case of an exothermic reaction increasing heat, which would shift the equilibrium to the reverse, endothermic direction?

 

[mw18]

In an exothermic rxn heat is a product. So if the reaction is at equilibrium, adding heat will shift the reaction to the left. Taking heat away will shift the reaction to the right (this is a common practice to use up all the reactants and increase yield).

In an endothermic rxn, heat is a reactant. If the reaction is at equilibrium, adding heat will shift the reaction to the right. Taking heat away will shift the reaction to the left.

Labrat07 has them backwards for endothermic. He/she has them the same for both reactions. Adding heat to endothermic creates more product (shifts right). Taking heat away from endothermic creates less product.

 

[Labrat07]

@mrwoods18 is right. I had it backward for the endorthermic. My apology.

 

[studentdocftw]

The easiest way to approach LeChatelier's problems is to assume the system WANTS to return to its initial state....thus, if you increase temperature, the system wants to find a way to decrease the temperature. Thus, the side of the reaction WITHOUT heat will be favored.
A + B --> heat + C increase in temp, it'll shift left to "lower" the heat
A + heat --> B + C increase in temp, it'll shift right to "lower" the heat

The same can be applied to pressure...increase the pressure, the system wants to decrease the pressure, thus side with less mols of gas will be favored. decrease the pressure, the system wants to increase the pressure, the side with more mols of gas will be favored. The same ideas can be applied to basically anything you might be asked on LeChatelier's