Equilibrium/Le Chatetier's principle

[Temperature101]

I am having a tough time conceptualizing this concept...

Here is an example on BR that I dont get:


Which of the following is the result of cooling an endothermic reaction that starts at equilibrium?

A. The amount of products decreases.
B. The amount of reactant decreases.
C. The equilibrium constant increases.
D. All partial pressures increase.

The answer is A. I got it by process of elimination since I know C and D are definitely false because decreasing temperature will decrease equilibrium constant (Kp) and partial pressure. Since the Kp decreases, either the amount of products decreases or the amount of reactants increases. BR explains the answer in a weird way that I dont get.

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[milski]

Exothermic reactions - heat is a product, endothermic reactions - heat is a reagent.
You have endothermic reaction and you are cooling it down, so heat is on the left and you are decreasing it. According to Le Chatelier's principle the equilibrium will shift to the left, which means less products.

 

[drdrdrdrdrdrdr]

My reasoning would be the following. You can think of an endothermic reaction as

heat + A + B --> C + D (as an example)

If you are cooling this endothermic reaction, then you are reducing the heat on the reactant side. By Le Chatelier, then you know that the reaction would shift to the left side, which would mean increase in reactants.

Hope that helps!

 

[Temperature101]

I got it now...Thanks

 

[MedPR]

I am having a tough time conceptualizing this concept...

Here is an example on BR that I dont get:


Which of the following is the result of cooling an endothermic reaction that starts at equilibrium?

A. The amount of products decreases.
B. The amount of reactant decreases.
C. The equilibrium constant increases.
D. All partial pressures increase.

The answer is A. I got it by process of elimination since I know C and D are definitely false because decreasing temperature will decrease equilibrium constant (Kp) and partial pressure. Since the Kp decreases, either the amount of products decreases or the amount of reactants increases. BR explains the answer in a weird way that I dont get.

Endothermic:
Reactant + Heat ----> Product

Exothermic:
Reactant -----> Product + Heat

Le Chatelier's principle says that adding to one side pushes equilibrium to the other side.