Patterns of problems

## Equilibrium

1
Factors affecting equilibrium - Le Chatelier's principle Description: Most of the questions asked from this topic would ask you to investigate the change in the equilibria or equilibrium constant if one of the external factors like pressure, temperature, etc., is changed. How to Approach: According to Le chatelier's principle, If a chemical reaction is at equilibrium and experiences a change in pressure, temperature, or concentration of products or reactants, the equilibrium shifts in the opposite direction to offset the change. Hence, to solve these questions you should have a basic understanding of the Le Chatelier's principle and how the equilibrium would shift to counter the change in each of the external factors.
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2
Calculating the Equilibrium constant or equilibrium concentrations of reactants and products Description: Most of the questions asked from this topic involve calculating the equilibrium constant or the equilibrium concentration of the reactants and products on the basis of the given data. How to Approach: To solve questions, you should know how to write the expression for equilibrium constant. To find the equilibrium concentrations , you can follow these simple steps:
• Write the balanced chemical equation.
• Convert the concentration given into moles/litre i.e. molarity.
• Make a note of the initial concentration and the change in concentration for each substance at equilibrium.
• Write the expression of equilibrium constant () and calculate the equilibrium concentrations of each reactant and product.
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3
Manipulation of the equilibrium constant Description: Questions asked from this topic require you find out the equilibrium constant if the reaction is reversed, multiplied or divided by a coefficient, or added to any other reaction in order to give a new reaction etc.
How to approach-
Reverse of a reaction
If a reaction,
has equilibrium constant as , then will have an equilibrium constant of
Multiplication of the reaction with a coefficient
If a reaction,
has equilibrium constant as , then will have an equilibrium constant of