Chemical Equilibrium Flashcards
Give an example of a reversible reaction.
Phosphorus-V chloride decomposed upon heating in a closed vessel to form chlorine and phosphorus-III chloride which will also react to give phosphorus-V chloride.
PCl₅⇆PCl₃ + Cl₂
Why does a reversible reaction not go to “completion”?
Because the products of the reaction react to form the original reactants.
What is the mixture finally obtained in chemical equilibrium called?
The equilibrium mixture.
Give some examples of reversible reactions.
N₂+3H⇆2NH₃
H₂+I₂⇆2HI
CH₃COOH+C₂H₅OH⇆CH₃COOC₂H₅+H₂O
How do we show that the equilibria are dynamic not static?
By using radioactive labelling experiments.
What happens to a reaction when equilibrium is reached?
Both the forward and reverse reactions do not stop but continue at the same rate.
What is the purpose of Le Chatelier’s Principle?
This is a general rule which can be used to predict the effect of changes in conditions of on a reaction in an equilibrium state.
What does Le Chatelier’s Principle state?
“if a system is in a state of dynamic equilibrium, then changes in temperature, pressure or concentration of reactants will cause the system to change in such a way as to tend to cancel out the imposed change.”
Considering the reaction: PCl₅⇆PCl₃ + Cl₂
What will happen if the pressure on the system is increased?
More PCl₅ will be formed as there are less molecules and therefore a smaller volume on the left of the equation. (One mole on the left, two moles on the right.) So if the equilibrium moves to the left there will be fewer molecules overall and so the pressure will be reduced.
Considering the reaction: PCl₅⇆PCl₃ + Cl₂
What will be the effect of an increase in temprature on the position of equilibrium?
The forward reaction is endothermic so if the temperature is increased more PCl₃ and Cl₂will be formed as the forward reaction rate increases (more than the backwards reaction rate increases) thereby reducing the temprature.
Considering the reaction: PCl₅⇆PCl₃ + Cl₂
What will be the effect of introducing more chlorine?
More PCl₅ will be formed thus removing the added chlorine by reacting with PCl₃.
What effect does a catalyst have on the equilibrium state?
No effect as it speeds up both reaction directions equally so does not affect the position of equilibrium. It just means that the system reaches equilibrium faster.
