Chemical Equilibria
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Le Chatelier’s principle refers to dynamic equilibrium. State what is meant by ‘dynamic’
Both forward and reverse reactions take place
Le Chatelier’s principle refers to dynamic equilibrium. State what is meant by ‘equilibrium’
Reactions take place at equal rates The concentration of all reactants and products remain constant
What is Le Chatelier’s principle?
If a system is disturbed, the position of the equilibrium moves in the direction to oppose the change It can be used to predict the effects of changes in temperature, pressure and concentration on the position of equilibrium in homogeneous reactions.
How do catalysts affect equilibrium?
They have no effect on the position, but do affect the time it takes for equilibrium to be reached as it equally increases the rate of reaction of both the forwards and backwards reaction
State what is meant by Kc
Kc is a value calculated from the equilibrium concentrations for a system at constant temperature Kc = concentration of products/concentration of reactants
Give the general formula for Kc for reaction wA +xB == yC + zD
Kc = ([C]^Y x [D]^Z)/([A]^W x [B]^X)
What are the features of a reaction in dynamic equilibrium?
1) forward and backward reactions are occurring at the equal rates 2) the concentrations of reactants and products stays constant
What are the factors affecting equilibrium?
concentration pressure temperature
For a reaction A <-> B, how does the concentration affect the equilibrium position and the yield of product?
an increase in [A] will shift the equilibrium position to the right, meaning the yield of product is higher a decrease in [A] will shift the equilibrium position to the left, meaning the yield of product is lower
For a reaction N2O4 (g) <-> 2NO2 (g), how does the pressure affect the equilibrium position and the yield of product?
increasing pressure of system, equilibrium shifts to the left as it moves to the side with fewer gas molecules, meaning yield of product decreases. decreasing pressure of the system, equilibrium position shifts to the right as it moves to the side with more gas molecules,meaning yield of product increases
For a reaction N204 (g) <-> 2NO2 (g) /\H = +57.2, how does the temperature affect the equilibrium position and the yield of product?
increasing temperature of the system, equilibrium moves in the endothermic direction, so shifts to the right, meaning yield of product increases decreasing temperature of the system, equilibrium moves in the exothermic direction, so shifts to the left, meaning yield of product decreases
What factors affect and dont affect Kc?
Pressure and concentration do not affect kc, whereas temperature does affect Kc.
How does is the value of Kc affected with an increase in temperature?