What is Le Chatelier's principle?

if a chemical system at equilibrium is subjected to a change in concentration, pressure or temperature, the position of equilibrium will shift to counteract the change.

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Why is Le Chatelier's principle useful?

It allows you to predict the affect of any changes made to a system at equilibrium.

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According to Le Chatelier's principle, what happens if you decrease the temperature?

The position of equilibrium will shift in the exothermic direction, to produce more heat (and counteract the decrease in temperature).

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According to Le Chatelier's principle, what happens if you increase the temperature?

The position of equilibrium will shift in the endothermic direction in order to decrease the temperature (and counteract the increase in temperature).

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According to Le Chatelier's principle, what happens if you increase the pressure?

The equilibrium will shift to the side with fewer molecules (moles) of gas, to reduce the pressure (and counteract the increase in pressure).

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According to Le Chatelier's principle, what happens if you decrease the pressure?

The equilibrium will shift to the side with more molecules (moles) of gas, to increase the pressure (and counteract the decrease in pressure).

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According to Le Chatelier's principle, what happens if you increase the concentration of the reactants?

The equilibrium will shift to the right (products side), to reduce the reactant concentrations and restore equilibrium.

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According to Le Chatelier's principle, what happens if you decrease the concentration of the reactants?

The equilibrium will shift to the left (reactants side), to increase the reactant concentrations and restore equilibrium.

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According to Le Chatelier's principle, what happens if you add a catalyst?

A catalyst will have no effect on the position of equilibrium.

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Why does a catalyst have no effect on the position of equilibrium?

A catalyst increases the rate of both forward and reverse reactions by the same amount so the position of equilibrium remains unchanged.


A catalyst does, however, increase the rate at which an equilibrium is established.

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Give 3 considerations that influence the conditions used for a reversible reaction in industry.

1The position of equilibrum.

2The rate of reaction.

3The costs of building and running the plant.

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What 3 factors alter the position of equilibrium?

  1. Concentration of reactants and products.
  2. Pressure (only affects gases).
  3. Temperature.

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