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Edexcel IGCSE Chemistry 復(fù)習(xí)筆記 3.3.3 The Position of Equilibrium

Category: IGCSE課程, 國際課程, 教材筆記 Date: 2022年7月15日下午12:33

Edexcel IGCSE Chemistry 復(fù)習(xí)筆記 3.3.3 The Position of Equilibrium

Factors that Affect the Position of Equilibrium

?When a change is made to the conditions of a system at equilibrium, the system automatically moves to?oppose?the change
- This is known Le Chatelier’s Principle, but you are not required to know the name for the exam
The principle is used to predict changes to the position of equilibrium when there are changes in temperature or pressure

Effects of Temperature

6.2.6-Effect-of-Temperature-on-Equilbrium

ExampleIodine Monochloride reacts reversibly with Chlorine to form Iodine Trichloride

ICl ?????????????+ ?????????????Cl₂????????????????????????????ICl₃

Dark Brown? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?Yellow

When the equilibrium mixture is heated, it becomes?dark brown?in colour. How do we know whether the backward reaction is exothermic or endothermic?

Equilibrium has shifted to the left as the colour dark brown means that more of ICI is produced
Increasing temperature moves the equilibrium in the endothermic direction
So the backward reaction is endothermic

Effects of Pressure

6.2.7-Effect-of-Pressure-on-Equilbrium

ExampleNitrogen Dioxide can form Dinitrogen Tetroxide, a colourless gas

2NO₂?????????????? ?????????????N₂O₄

Brown Gas? ? ? ? ? ? ? ? ? ? ? ? Colourless Gas

What is the effect of an increase in pressure on the position of equilibrium?

- Number of molecules of gas on the left = ???2
- Number of molecules of gas on the right =? 1

An increase in pressure will cause equilibrium to shift in the direction that produces the smaller number of molecules of gas
So equilibrium shifts to the right

Exam Tip

When the conditions at equilibrium are changed, the system always responds by doing the?opposite.

Catalysts & Dynamic Equilibrium

Effect of catalyst on equilibrium position

The presence of a catalyst does?not?affect the position of equilibrium but it does increase the rate at which equilibrium is reached
This is because the catalyst increases the rate of?both?the forward and backward reactions by the same amount (by providing an alternative pathway requiring lower activation energy)
As a result, the?concentration?of reactants and products is nevertheless the?same?at equilibrium as it would be without the catalyst

Effect-catalyst-on-equilibrium-position Diagram showing the effect of catalyst on equilibrium position