Chemical Equilibrium

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Dynamic Equilibrium

Equilibria - reactants and products exist together, rather than going into completion.

Position of equilibrium - how far a reaction goes into completion. 

Dynamic Equilibrium involves two opposing processes that occur at equal rates. 

Macroscopic properties (visible processes) are constant, whilst microscopic (molecular, non-visible processes) continue to occur. 

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Nitrogen dioxide and dinitrogen tetroxide

In heavily polluted air, a brown haze may be seen. This is nitrogen dioxide, NO2 (formed by the oxidation of the nitrogen monoxide).

Nitrogen dioxide is in equilibrium with dinitrogen tetroxide, N2O4, which is colourless. 

A steady state is reached when the rate of conversion of reactant into products equals the rate of conversion of products into reactants. 

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Haber Process

Controlled equilibrium in order to keep a good yield of product.


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What affects equilibrium?

Le Chatelier's principle:

Whenever a system, which is in dynamic equilibrium, is disturbed, it responds in a way to oppose the disturbance and so restore equilibrium. 


If you increase the temperature, in an exothermic reaction, the equilibrium responds to oppose the change. The reaction moves in the endothermic direction. 


For a gaseous reaction pressure affects the particles. One mole of gas occupies the same volume, so at a constant pressure the reactants take up twice the space of the products.


For a reaction in an aqueous solution, increasing the concentration of reactants will drive the reaction to the right. 

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Iodine (I) chloride and iodine (III) chloride

If chlorine gas is passed through a U-tube containing solid iodine, a brown liquid is formed, Iodine (I) chloride

The bottom of the tub is hot - the reaction is exothermic. 

If more chlorine is passed through a yellow solid is formed, Iodine (III) chloride

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Equilibria in industry

Haber process

Controlled to maximise profits, by producing maximal yield. 

High pressure, shift to the right, procucing more ammonia.

Using a low temperature, as it exothermic, so would oppose the change, shifting right.

Using an iron catalyst to speed up the reaction.

Role of a catalyst

The haber process uses iron, but a ruthenium catalyst is more efficient. 

However, this is more expensive and requires a higher temperature. 

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Stored methane in equilibrium

Methane hydrate is in equilibrium with gaseous methane and water. 

The forward reaction is endothermic.

If the earths temperature rises, equilibrium will move to the right, to oppose the change, releasing more methane. 

An increase in pressure shifts the equilibrium to the left. Changing methane gas into methane hydrate.

It has been the sudden release of methane gas that can cause a rise in temperature. 

If ice structures melt huge amounts of methane could be released into the atmosphere. Acting a green house gas which would make it worse.

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