13 Le Chatellier-Braun principle, tuning the equilibrium
Le Chatellier-Braun principle, role of concentrations, temperature and pressure
Le-Chatelier-Braun principle
· if there is something acting on the equilibrium that disturbs the equilibrium state the system will shift the equilibrium to one side which can get rid of the disturbing factor (negative feedback)
· There are common things that can disturb equilibrium:
o Concentration
§ let’s take the general formula of an equilibrium reaction
·
§ the addition of A or B will result in a shift towards the products, since the system is trying to get rid of the excess initial material
§ the addition of C or D will result in a shift towards the initial materials, since the system is trying to get rid of the excess products
§ This can be related to the formula of Kc as well
· K
o Temperature
§ if we increase the temperature the system will shift towards the endothermic reaction (to cool the system), if we decrease the temperature the system will shift towards the exothermic reaction (to heat the system)
§ let’s take ammonia synthesis as an example
· exothermic reaction
§ if we increase T, the system is going to shift towards the initial materials to decrease the temperature with the endothermic reaction
§ this is in accordance to the van’t Hoff equation
·
o Pressure
§ K is only dependent on pressure in case there is a change in moles in the reaction and if we have Kx and gases in the reaction
§ The equilibrium will still be shifted, if we increase the pressure the system shift to the side with less moles (in this case towards the products) to decrease the pressure. if we decrease the pressure the equilibrium shifts towards the side with more moles to increase the pressure (in this case towards the initial materials)
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