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MED 102- GENERAL CHEMISTRY > CHEMICAL EQUILIBRIUM (PART 2) > Flashcards

CHEMICAL EQUILIBRIUM (PART 2) Flashcards

1
Q
  1. What are the steps to figure out this equation?
A
  1. We expand this equation
    • this turns into a quadratic equation
    • ax2 + bx + c = 0
    • this means that two possible solutions will be
      obtained
  2. The two terms in the denominator are the same
    • this means that the denominator is (0.100 - x)²
  3. If we cancel out the square roots, we are left with:
    • 2x/(0.100 – x) = (57.0)1/2
  4. This means that the system is now linear in x
    • all the x² are no longer present in the equation
  5. x is the change in the concentration
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2
Q
  1. What is Le Châtelier’s Principle?
A
  • if a stress is applied to a system that is at equilibrium:
    • the net reaction occurs in the direction that relieves
      the stress
  • 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
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3
Q
  1. Why is it important to manipulate the position of the equilibrium?
A
  • to produce as much product as possible using as little time (energy) as possible
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4
Q
  1. What process does this show?
A
  • the Haber Process
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5
Q
  1. What is the purpose of the Haber Process?
A
  • 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
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6
Q
  1. What is mixed together to form Ammonia?
A
  • 1 part of N2
    (non-polar)
  • 3 parts of H2
    (non-polar)
  • these two react
  • they then reach Equilibrium
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7
Q
  1. What are the conditions that the Ammonia reaction happens in?
A

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

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8
Q
  1. What happens when the equilibrium is reached in the Ammonia Reaction?
A
  • 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
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9
Q
  1. What happens to the Haber Process reaction when more N2 is added?
A
  • 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

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10
Q
  1. What happens to the Haber Process is we keep removing NH3?
A
  • the system is forced to use up all the reactants
  • this maximises the amount of NH3 formed
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11
Q
  1. What are the factors that influence the Chemical Equilibrium in relation to Le Chatêlier’s Principle?
A
  1. Changes in Concentration
  2. Changes in Pressure and Volume
  3. Changes in Temperature
  4. The Effect of a Catalyst
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12
Q
  1. What happens to the Haber Proccess equation when Hydrogen Gas is added?
A

THE FINAL CONCENTRATIONS
- are different from the initial concentrations

THE EQUILIBRIUM CONSTANT (KC VALUE) DOES NOT CHANGE:
- provided that the temperature stays constant

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13
Q
  1. What happens to the Haber Process when we reduce the volume?
A

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
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14
Q
  1. What can be said about the Pressure and the Volume of these systems?
A
  • 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
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15
Q
  1. How will this reaction behave when the pressure is decreased?
A
  • 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
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16
Q
  1. What happens to the Haber Process when it is an Exothermic Process?
A
  • 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
17
Q
  1. What happens to the Haber Process when it is an Endothermic Reaction?
A
  • 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

18
Q
  1. What is the effect of a catalyst on Chemical reactions?
A
  • 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
19
Q
  1. Is the Haber Process Exothermic or Endothermic?
A
  • exothermic
20
Q
  1. What happens to the Exothermic Haber Process when the temperature is increased?
A
  • the equilibrium position will shift to the left
  • this makes less NH3
21
Q
  1. What happens to the Exothermic Haber Process when the temperature is decreased?
A
  • 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
22
Q
  1. Which is the best temperature to use for the Haber Process?
A
  • a medium temperature
  • this is a compromise between the position and the
    rate of the reaction
23
Q
  1. In an exam, what condition maximises the NH3 amount?
A
  • high pressure
  • low temperature
  • this is according to Le Chatêlier’s Principle
24
Q
  1. What can you predict when you know the Kc value?
A
  • you can predict whether the reaction will be spontaneous or spontaneous
25
Q
  1. What equation do we use when we want to figure out whether a reaction will be spontaneous or non-spontaneous?
A
  • ▵Gθ = ▵H- T▵S
  • ln = -log
  • K = Kc / Kp
26
Q
  1. What does a positive ▵G value indicate?
A
  • non spontaneous process
  • small Kc
  • very little product produced
27
Q
  1. What does a negative ▵G value indicate?
A
  • spontaneous process
  • high Kc
  • lots of product produced
28
Q
  1. Read through this summary.
    Does everything make sense?
A
  • yes

MED 102- GENERAL CHEMISTRY (27 decks)

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