CHEMICAL EQUILIBRIUM (PART 2) Flashcards
- What are the steps to figure out this equation?
- We expand this equation
- this turns into a quadratic equation
- ax2 + bx + c = 0
- this means that two possible solutions will be
obtained
- The two terms in the denominator are the same
- this means that the denominator is (0.100 - x)²
- If we cancel out the square roots, we are left with:
- 2x/(0.100 – x) = (57.0)1/2
- This means that the system is now linear in x
- all the x² are no longer present in the equation
- x is the change in the concentration
- What is Le Châtelier’s Principle?
- if a stress is applied to a system that is at equilibrium:
- the net reaction occurs in the direction that relieves
the stress
- the net reaction occurs in the direction that relieves
- the system will aim to maximise the yield of the
product - the system will aim to minimise the time taken to
produce the products - the system will always aim to return to Equilibrium
- Why is it important to manipulate the position of the equilibrium?
- to produce as much product as possible using as little time (energy) as possible
- What process does this show?
- the Haber Process
- What is the purpose of the Haber Process?
- it is used for making ammonia from its elements
- Nh3
- NH3 consists of hydrogen bonding and London forces
- it has a high boiling point
- Ammonia is used to make fertilisers
- What is mixed together to form Ammonia?
- 1 part of N2
(non-polar) - 3 parts of H2
(non-polar) - these two react
- they then reach Equilibrium
- What are the conditions that the Ammonia reaction happens in?
TEMPERATURE:
- 400°C to 450°C
- this is a medium/intermediate temperature
PRESSURE:
- 200 atm
- this is a very high pressure
IRON CATALYST IS USED:
- this speeds up the reaction
- this saves energy
- this saves electricity
- this minimises the time used to maintain the high
pressures and temperatures
- What happens when the equilibrium is reached in the Ammonia Reaction?
- the gas mixture cools down
- the condensation point of NH3 is the
highest - it will be reached first
- this is because NH3 is polar
- NH3 will turn into a liquid
- this means that it can be easily removed from the
reaction container - a higher temperature will cause the H2 and the N2 to
react - the H2 and N2 gases are recycled
- this gives more NH3
- H2 and N2 have London Forces
- this means that they have a lower boiling point
- this process is repeated until everything reacts
- What happens to the Haber Process reaction when more N2 is added?
- this means that more reactants are added
- the system moves towards the right
- the system now uses up more reactants
- the Qc Value is reduced
TO INCREASE THE QC VALUE BACK TO THE KC VALUE:
- more NH3 is made
- this uses up more H2 and N2
REMOVING THE NH3:
- the reaction moves to the left
- reduces the value of the Qc
- this forces the system to make more NH3
- What happens to the Haber Process is we keep removing NH3?
- the system is forced to use up all the reactants
- this maximises the amount of NH3 formed
- What are the factors that influence the Chemical Equilibrium in relation to Le Chatêlier’s Principle?
- Changes in Concentration
- Changes in Pressure and Volume
- Changes in Temperature
- The Effect of a Catalyst
- What happens to the Haber Proccess equation when Hydrogen Gas is added?
THE FINAL CONCENTRATIONS
- are different from the initial concentrations
THE EQUILIBRIUM CONSTANT (KC VALUE) DOES NOT CHANGE:
- provided that the temperature stays constant
- What happens to the Haber Process when we reduce the volume?
A REDUCTION IN VOLUME:
- leads to an increase in pressure
- this will favour the side with the fewest moles (n) of
gas
ACCORDING TO LE CHATÊLIER’S PRINCIPLE:
- the system acts to reduce the pressure
- it does this by decreasing the moles of gas (n)
IN THE CASE OF THE HABER PROCESS:
- a decrease in volume will favour the product (NH3)
- this is because there are less moles (n) present
- the system shifts to the right
- the system makes more NH3
- this is why there are high pressures present for the Haber Process
- What can be said about the Pressure and the Volume of these systems?
- the number of moles of gas is the same on both sides
- changing the pressure has no effect on the
equilibrium position - the system is powerless
- there will not be any pressure changes
- How will this reaction behave when the pressure is decreased?
- there is one moles of the gas on the left side
- there are 2 moles of gas on the right side
- the system will shift to the left
- it favours the products side
- this is the side with fewer moles
- What happens to the Haber Process when it is an Exothermic Process?
- heat is considered as a product
IF WE RAISE THE TEMPERATURE:
- the system will perceive it as an input of heat
(product)
- this will shift the reaction to the left side
- What happens to the Haber Process when it is an Endothermic Reaction?
- heat is considered as a reactant
- the heat is added to the reactants side
INCREASING THE TEMPERATURE:
- the heat is added like a reactant
- the equilibrium will shift to the right side
- What is the effect of a catalyst on Chemical reactions?
- a catalyst speeds up the reaction rate
- it does not effect the equilibrium position
- the forward and the reverse reactions are affected to
the same degree - you will still be receiving the same amount of product
- just at a much faster rate
- Is the Haber Process Exothermic or Endothermic?
- exothermic
- What happens to the Exothermic Haber Process when the temperature is increased?
- the equilibrium position will shift to the left
- this makes less NH3
- What happens to the Exothermic Haber Process when the temperature is decreased?
- the equilibrium position will shift to the right
- this will slow down the reaction
- this will make more ammonia
- it will make the ammonia at a slower rate
- this is not good for the industrial process
- a slower process takes more time and energy to
complete
- Which is the best temperature to use for the Haber Process?
- a medium temperature
- this is a compromise between the position and the
rate of the reaction
- In an exam, what condition maximises the NH3 amount?
- high pressure
- low temperature
- this is according to Le Chatêlier’s Principle
- What can you predict when you know the Kc value?
- you can predict whether the reaction will be spontaneous or spontaneous
- What equation do we use when we want to figure out whether a reaction will be spontaneous or non-spontaneous?
- ▵Gθ = ▵H- T▵S
- ln = -log
- K = Kc / Kp
- What does a positive ▵G value indicate?
- non spontaneous process
- small Kc
- very little product produced
- What does a negative ▵G value indicate?
- spontaneous process
- high Kc
- lots of product produced
- Read through this summary.
Does everything make sense?
- yes
