chemical equilibrium

[BodybldgDoc]

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PCl5 + 4H20 ---> H3PO4 + 5HCl Delta H = -527KJ

In the above reaction, if the temperature is increased, which direction would the reaction be shifted? To the left or to the right? and why?

 

[twohearted]

I believe that since the rxn has a neg. delt. h, it would be considered exothermic. So heat could be written as a product: PCl5 +4H20 -> H3po4 + 5hcl + heat. L'chatliers principle states that when a perturbance in equilibrium occurs, the reaction will be shifted away from the perturbance (paraphrasing here.) Now if the heat would increase, I would think that the rxn would have to go left to resume equilibrium. Does that seem right?

 

[BodybldgDoc]

you are correct. thank you for the explanation.

 

[ATLATLATL]

my question is...say for instance if the temperature increased or decreased then which way would it shift?
and if it was endothermic...then?

 

[BodybldgDoc]

my question is...say for instance if the temperature increased or decreased then which way would it shift?
and if it was endothermic...then?

If it was endothermic, then the heat can be written as a reactant. so If you increase the heat from the side of the reactants it will shift towards the right i.e toward the products to bring the equation back to equilibrium.

 

[Lonely Sol]

my question is...say for instance if the temperature increased or decreased then which way would it shift?
and if it was endothermic...then?

If temp. increases and endothermic = goes to right (forward)
If temp. decreases and endothermic = goes to left

If temp increase and exothermic = goes to left
If temp decreases and exothermic = goes to right

 

[twohearted]

my question is...say for instance if the temperature increased or decreased then which way would it shift?
and if it was endothermic...then?

Lets generalize. Exothermic means Delta H < 0. Heat is a product so: Reactants -> Products + heat. This is the case for the example given. So if heat were added to the system, we must go to the left to restore equilibrium. This is intuitive because if the ratio of the products to reactants must be constant (equilibrium constant Keq), then it must follow that the addition of product would disturb the system such that the rxn would move to form more reactant so that the ratio remain the same(moves left.) Now then, if the heat in this exothermic system (Reactants -> Products + heat), were to be decreased, then naturally more product must be formed to keep that ratio constant (rxn goes right.) For an endothermic rxn we have: Reactants + Heat -> Products. So increasing the heat would drive the rxn to the right, so that the ratio is restored. Likewise lowering the heat in such a system would cause the reaction to move left. If I am completely wrong here, someone please correct me, but it seems pretty intuitive.

 

[Nasem]

For endothermic:
Reactants + head <-----> Product, H is +
If you +T, shift right --->
If you -T, shift left <---



For exothermic:
Reactants <-----> Product + heat, H is -
If you +T, shift left <---
If you -T, shift right --->