Chemical Equilibrium Flashcards
What is Chemical Equilibrium?
Chemical equilibrium is the state in which the rate of the forward reaction equals the rate of the reverse reaction
What is the formula for Kc?
[products]moles / [Reactants]moles
Note: In the cases of numerous products/Reactants., use the exponent on each one and then add them
What does the value of Kc depend on at equilibrium?
Temperature
Why is chemical equilibrium dynamic?
Chemical equilibrium is dynamic as the forward and reverse reactions are continuously occurring
What happens Kc if the forward reaction is exothermic and the temperature increases
It decreases
What happens Kc if the forward reaction is endothermic and the temperature increases
It increases
What is Le Chatelier’s principle
When a system at equilibrium is subjected to stress, the equilibrium shifts in such a way to minimise the effect of stress.
What happens to a reaction at equilibrium if there is a change in concentration of one species
- If the species concentration decreases, the reaction that produces more of that species is favoured
- If the species concentration increases, the reaction that uses the that species as a reactant is favoured
What happens to a reaction at equilibrium, if the temperature is changed?
- If the temperature increases, the reaction that is endothermic is favoured
- If the temperature decreases, the reaction that is exothermic is favoured
What happens to a reaction at equilibrium, if a catalyst is added?
Nothing. The catalyst spped up the forward and reverse reaction equally
What happens to a gas reaction at equilibrium, if the pressure changes?
- If the pressure increases, the reaction(if there is one) that produces less molecules will be favoured
- If the pressure decreases, the reaction(if there is one) produces more molecules is favoured
What is the process, ammonia synthesis more commonly called?
The Haber process
What is the ammonia synthesis equation?
N2 + 3H2 2NH3
At what temperature does the Haber process take place?
As the forward reaction is exothermic, a low temperature would be efficent, however to keep the rate of reaction high, the temperature is 673K.
At what pressure does the Haber process take place?
As the product of the forward reaction contsists of two moles while the reactants consists four moles, an increase of pressure would favour the forward reaction.
As a result, the Haber process occurs at 200 atms
What catalyst is used in the Haber process?
Iron based catalysts ( Fe2 Fe3, Fe2O etc)
What is the process of making sulfur trioxide called?
The Contact process
What is the equation for the Contact process reaction?
SO2 + 1/2O2 SO3
At what temperature does the Contact process take place
The forward reaction is exothermic, so a low temperature would increase the productoin of sulfur trioxide. However, to keep the rate of reaction relatively high, a temperature of 713K is used
What pressure does the Contact process occur at?
As only 1 mole is produced and 3/2 moles react in the forward reaction, a higher pressure would favour the forward reaction. However, only a pressure of about 1 atm is used. A good enough yield is produced at this pressure and higher pressures can not be economically justified.
What happen with regard to the concentration of Sulfur trioxide as the Contact process reaction occurs?
The sulfur trioxide is removed, thus the foward reaction which produces sulfur trioxide is favoured and more sulfur trioxide is produced.
What catalyst is used in the Contact process?
Vandium Pentoxide ( VO5)
Why are industrial reactions such as the Haber process and the Contact process not allowed to reach equilibrium?
As a reaction gets closer to equilibrium, the rate of increase in yield slows down. It is not economical in industry to wait for maximium yield of the reaction
