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MED 102- GENERAL CHEMISTRY > CHEMICAL EQUILIBRIUM (PART 1) > Flashcards

CHEMICAL EQUILIBRIUM (PART 1) Flashcards

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1
Q
  1. What is Chemical Equilibrium?
A
  • it is the state where the concentrations of the reactants
    and the products do not appear to change
  • the forward rate and the reverse rate must be equal
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2
Q
  1. What is the Equilibrium Mixture?
A
  • it is the mixture of the reactants and the products at
    equilibrium
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3
Q
  1. What is the concept of Equilibrium only applicable to?
A
  • it is only applicable to reversible reactions
  • these reactions are bi-directional
  • this can be said for many chemical reactions
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4
Q
  1. What can be inferred from this graph?
A

This graph depicts a Dynamic Equilibrium

AS THE REACTION PROCEEDS FORWARD:
- it forms products
- the reverse reaction starts forming

AT SOME POINTS:
- the rates of the forward reaction and the reverse
reactions become equal
- the reaction appears to stop at this point

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5
Q
  1. In order dynamic equilibrium to be established, what characteristic must the process have?
A
  1. it needs to be reversible
    • this means that it has both forward and reverse
      reactions
  2. the system is closed
    - this means that no escape of matter is possible
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6
Q
  1. What is happening at Dynamic Equilibrium?
A
  • both the forward and the reverse reactions are taking
    place
  • they are happening at equal rates
  • this means that we see no change in the amount of
    reactants or products
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7
Q
  1. Provide one example of a system in Dynamic Equilibrium?
A
  • a container in which water is entering water at the
    same time as water is leaving the container
  • water is entering the container at the same rate as
    water is leaving the container
  • the level of the water in the tank will not change
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8
Q
  1. Why do many reactions not undergo completion?
A
  • there are competing reverse reactions
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9
Q
  1. What can be observed about the state of this reaction?
A
  • equilibrium can be observed from either end
  • the same equilibrium mixture will result at a given
    temperature

AT EQUILIBRIUM:
- the colour of the substances is no longer changing
- the forward and the reverse reactions are still ongoing
- their rates become equal
- there is no net change in the equilibrium mixture

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10
Q
  1. What can be observed about the state of this reaction at a temperature of 273K?
A
  • the equilibrium lies heavily to the left
  • the container looks colourless
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11
Q
  1. What can be observed about the state of this reaction at a temperature of 373K?
A
  • the equilibrium lies heavily to the right
  • the container looks dark brown
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12
Q
  1. What can be observed about the colour of this reaction at a temperature between 273K and 373K?
A
  • the colour is a different shade of brown
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13
Q
  1. What can be observed about the state of this reaction at a temperature right in the middle of 273K and 373K (323) and as only N2O4 is being added to the container ?
A
  • the colour will start turning brown
  • NO2 will be formed

A NEW EQUILIBRIUM WILL BE REACHED:
- the brown colour will stop changing

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14
Q
  1. What can be observed about the state of this reaction at a temperature right in the middle of 273K and 373K (323) and as only NO2 is being added to the container ?
A
  • the colour will start turning to lighter brown
  • it will eventually become colourless
  • N2O4 is formed

A NEW EQUILIBRIUM WILL BE REACHED:
- the much lighter brown colour will stop changing

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15
Q
  1. What is the Kc value?
A
  • it is the Equilibrium Constant
  • the c in Kc means concentration/molarity
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16
Q
  1. How do we write the Equilibrium Equation?
    (the Kc value equation)
A
17
Q
  1. What does a large Kc refer to?
A
  • mostly products existing
  • it favours the right hand side of the equation
  • the equilibrium lies to the right
  • it favours the forward reaction
18
Q
  1. What does a small Kc refer to?
A
  • mostly reactants
  • it favours the left hand side of the equation
  • the equilibrium lies to the left
  • it favours the reverse reaction
19
Q
  1. What is the only factor that affects the Kc value?
A
  • the temperature that the reaction is occurring in

A HIGHER TEMPERATURE:
- a higher Kc value

A LOWER TEMPERATURE:
- a lower Kc value

20
Q
  1. How do we write the Equilibrium Constant for the Reverse Reaction?
A
  • 1 / Kc
  • this is called Kc prime (K’c)
  • it changes around the order of the products and the
    reactants in the equation
21
Q
  1. How do we write the Equilibrium Constant for the Forward Reaction?
A
  • Kc
22
Q
  1. Do you understand this image?
A
  • yes
23
Q
  1. In this equation, what does ▵n represent?
A
  • it is equal to the products minus the reactants
  • it is only applicable to gases and their coefficients
24
Q
  1. In this system, what is the ▵n equal to?
A

▵n = products - reactants
= 2 moles of gas products - 1 mole of gas products
= 1

25
Q
  1. In this system, what is the ▵n equal to?
A

▵n = products - reactants
= 2 moles of gas products - 2 mole of gas products
= 0

  • (RT)⁰ = 1
  • this means that Kc = Kp
26
Q
  1. What is a Homogenous Equilibrium?
A
  • the reactants and the products are all in the same phase
  • all the elements in the reaction are either gases or aqueous solutions
27
Q
  1. What is a Heterogeneous Equilibrium?
A
  • the reactants and the products are all in different phases
  • there are liquid, solid and gas elements present in the equation
28
Q
  1. How would you write the Equilibrium Constant Equation for this reaction?
A
  • pure solids and pure liquids are not included in the equilibrium expression
  • their concentrations would be constant throughout the chemical reaction
  • they are not necessary in the Equilibrium Constant Equation
29
Q
  1. Why does the density of a pure solid or a pure liquid not change during a chemical reaction?
A
  • both the mass and the
    volume decrease
  • this keeps the density
    constant
30
Q
  1. What does the Kc value of this reaction indicate?
A
  • the Kc value is large
  • the numerator (top) value is much bigger than the
    denominator (bottom) value
  • there are many more products present
  • the equilibrium lies heavily to the right
31
Q
  1. What does the Kc value of this reaction indicate?
A
  • the Kc value is very small
  • the bottom fraction is much bigger than the top
  • there are more reactants present
  • the equilibrium lies heavily to the left
32
Q
  1. What is Qc?
A
  • it is essentially the same as the Kc value
  • except it uses the initial concentrations of the elements
  • it makes use of the exact same equation as the Kc
    value
33
Q
  1. What will happen to the reaction if the Qc is less than the Kc? (Qc < Kc)
A
  • the reaction will move to the right to establish a new equilibrium
  • the products will increase
  • the reactants will decrease
34
Q
  1. What will happen to the reaction if the Qc is more than the Kc? (Qc > Kc)
A
  • the reaction will move to the left to establish a new equilibrium
  • the products will decrease
  • the reactants will increase
35
Q
  1. What will happen to the reaction if the Qc is equal to the Kc? (Qc = Kc)
A
  • the products will not change
  • the reactants will not change
  • the reaction is at equilibrium
36
Q
  1. Read through this summary.
    Does everything make sense?
A
  • yes

MED 102- GENERAL CHEMISTRY (27 decks)

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