3.1.6 Chemical Equilibria And Le Chatelier’s Principle Flashcards
What is a reversible reaction?
When the reaction goes both forwards and backwards, so the products are formed from the reactants, but the reactants are also reformed from the products.
What is dynamic equilibrium?
Dynamic equilibrium is when the rate of the forwards reaction and reverse reaction are equal so there is no net change in the concentration of reactants or products.
What are the features of a reaction at equilibrium?
Forwards and reverse reactions proceed at equal rates.
The concentrations of reactants and products remain constant.
What is a closed system?
When nothing can enter or exit the reaction mixture and nothing new is added.
What is le chatelier’s principle?
If a change is imposed on a reaction at equilibrium, the position of equilibrium will move to oppose the change made.
What can be changed in an equilibrium reaction?
The temperature, the concentration or the pressure
What happens is equilibrium shifts to the left?
We obtain a higher yield of reactants
What happens is equilibrium shifts to the right?
We obtain a higher yield of products
What happens if we increase the concentration of reactants at equilibrium?
Equilibrium shifts to the right, to oppose the increase in concentration of reactants. This increases the yield of the products.
What happens if we increase the concentration of products at equilibrium?
Equilibrium shifts to the left, to oppose the increase in concentration of products. This increases the yield of the reactants.
When does increase/decrease in pressure affect the position of equilibrium?
In a gaseous system
What happens if we increase the pressure of a reaction at equilibrium?
Equilibrium shifts to the side with fewer moles, to oppose the increase in pressure and decrease the pressure.
What happens if we decrease the pressure of a reaction at equilibrium?
Equilibrium shifts to the side with more moles, to oppose the decrease in pressure and increase the pressure.
What happens if we increase the temperature of a reaction at equilibrium?
Equilibrium shifts in the endothermic direction, to oppose the increase in temperature by decreasing the temperature.
What happens if we decrease the temperature of a reaction at equilibrium?
Equilibrium shifts in the exothermic direction, to oppose the decrease in temperature by increasing the temperature.
What is the equation for making ethanol?
C2H4 + H20 -> C2H5OH
What are the conditions for making ethanol?
60 atmospheres
300*c
Phosphoric acid catalyst
Why is a temperature of 300*c used for making ethanol?
The forwards reaction is exothermic. If we decrease the temperature, equilibrium shifts to the right, in the exothermic direction, to oppose the decrease in temperature. This means a higher yield of ethanol is obtained.
However, low temperature means a slow rate of reaction, so a compromise temperature between yield and rate of reaction is used.
Why is a pressure of 60atm used for making ethanol?
We increase the pressure, so equilibrium shifts to the right as it is the side with fewer moles, to oppose the increase in pressure by decreasing the pressure, so the yield of ethanol increases.
This produces a good yield and has a fast rate of reaction.
However a compromised pressure is used between yield and rate, and cost of strong reaction vessels/equipment.
What is the equation for the Haber process?
3H2 + N2 -> 2NH3
What are the conditions for the haber process?
450*c
200 atmospheres
Iron catalyst
What is the haber process used for?
To manufacture ammonia for…
Fertilisers
Nylon
Explosives
Drugs
Dyes
Why is a temperature of 450*c used for the haber process?
If we decrease the temperature, equilibrium shifts to the right in the exothermic direction, to oppose the decrease in temperature. This increases yield of ammonia.
This produces a high yield but low temperatures means a slow rate of reaction, so a compromise temperature is used.
Why is a pressure of 200 atmospheres used in the haber process?
If we increase the pressure, equilibrium shifts to the right, as it is the side with fewer moles, to oppose the increase in pressure. This increases the yield of ammonia.
This produces a good yield and a fast rate of reaction.
However, a compromised pressure between yield and rate, and cost of strong reaction vessels/equipment is used.
What is Kc?
Equilibrium constant
How is Kc affected by a temperature change that causes equilibrium to shift to the right?
If equilibrium shifts right, then the concentration of the products increases.
This means the Kc ratio increases.
How is Kc affected by a temperature change that causes equilibrium to shift to the left?
If equilibrium shifts left, the concentration of the reactants will increase.
This means the Kc ratio decreases.
How is Kc affected by changes in concentration?
Kc is not affected by changes in concentrations to reactants or products.
Adding more of a reactants or products means equilibrium shifts to increase/decrease this concentration, so equilibrium is restored and therefore so is the original Kc ratio.
How is Kc affected by addition of a catalyst?
Kc is not affected by the presence of a catalyst as they speed up the rate of the forwards and reverse reactions equally so the Kc ratio remains the same.
