CHEMICAL EQUILIBRIUM (PART 1) Flashcards
1
Q
- 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
2
Q
- What is the Equilibrium Mixture?
A
- it is the mixture of the reactants and the products at
equilibrium
3
Q
- 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
4
Q
- 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
5
Q
- In order dynamic equilibrium to be established, what characteristic must the process have?
A
- it needs to be reversible
- this means that it has both forward and reverse
reactions
- this means that it has both forward and reverse
- the system is closed
- this means that no escape of matter is possible
6
Q
- 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
7
Q
- 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
8
Q
- Why do many reactions not undergo completion?
A
- there are competing reverse reactions
9
Q
- 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
10
Q
- 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
11
Q
- 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
12
Q
- 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
13
Q
- 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
14
Q
- 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
15
Q
- What is the Kc value?
A
- it is the Equilibrium Constant
- the c in Kc means concentration/molarity
16
Q
- How do we write the Equilibrium Equation?
(the Kc value equation)
A
17
Q
- 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
- 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
- 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
- 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
- How do we write the Equilibrium Constant for the Forward Reaction?
A
- Kc
22
Q
- Do you understand this image?
A
- yes
23
Q
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- Read through this summary.
Does everything make sense?
A
- yes
