Chemical Equilibrium

Question 1

What is dynamic equilibrium

Answer 1

A dynamic equilibrium is a chemical equilibrium
between a forward reaction and the reverse
reaction where the rate of the reactions are equal.

At this point, the ratio between reactants and
products remains unchanged over time.

Question 2

How does Reaction reversibility work?

Answer 2

The same equilibrium composition is reached from either forward or reverse direction, provided the overall system composition is the same.

Question 3

What can the magnitude of Kc give and list two examples

Answer 3

information about the reactant and product concentrations at equilibrium

Kc > 1 = - more products than reactants.
- equilibrium lies to the right.

Kc <1= - more reactants that products.
- equilibrium lies to the left.

Question 4

What is reaction quotient?

Answer 4

measures the relative amounts of products and reactants present during a reaction at a particular point in time.

expression for systems that are not at equilibrium

Question 5

What are the comparisons between Kc and Qc?

Answer 5

Kc involves equilibrium concentrations and refers to at equilibrium
- can have only one positive value at a particular temperature

Qc refers to systems that are no necessarily at equilibrium
- can have any positive values

when equilibrium is established, Qc = Kc.
Q < Kc = the system to use up products and generate more reactant as compared to the equilibrium. decreased Qc To achieve equilibrium, more product would have to be formed.

Q > Kc = the system is using up more rectants and generating more product as compared to equilibrium, more reactants would have been formed.

Question 6

What are the two types of chemical equilibrium?

Answer 6

Homogeneous equilibrium and heterogeneous equilibrium

Question 7

What is homogeneous equilibrium? and how are they classified?

Answer 7

All the reacting components are in one phase, or one state of matter like solid, liquid or gases

• These are classified into three types
• The reaction where no net change of mole
  numbers of the system (Δγ = 0).
• Mole numbers of the system increase due to
  reaction (Δγ = +ve).
• Mole numbers of the system decrease due to
  reaction (Δγ = −ve).

Question 8

What is heterogeneous equilibrium?

Answer 8

all the reacting components are not in one phase

Question 9

Describe what the Le Chateliers Principle is?

Answer 9

If a system at equilibrium is disturbed by a change
in temperature, pressure or the concentration of
one of the components, the system will shift its
equilibrium position so as to counteract the effect
of the disturbance.

Question 10

What are factors influence the Le Chateliers principle?

Answer 10

• Temperature
• Pressure
• Addition/Removal of Species
• Catalyst

Question 11

in relation to le chateliers principle, what happens when the temperature is increased?

Answer 11

What happens when we increase the temperature
of the system?
1. Increased temperature  system must
decrease temperature to restore equilibrium.
2. To decrease temperature  system must
absorb excess heat.
3. To absorb heat  system must favour the
endothermic reaction.
4. The equilibrium shifts to the left favouring the
backward reaction.
5. The equilibrium constant therefore decreases
with increasing temperature.

Question 12

in relation to le chateliers principle, what happens when the temperature is decreased?

Answer 12

1. Decreased temperature  system must
   increase temperature to restore equilibrium.
2. To increase temperature  system must
   release excess heat.
3. To release heat  system must favour the
   exothermic reaction.
4. The equilibrium shifts to the right favouring the
   forward reaction.
5. The equilibrium constant therefore increases
   with decreasing temperature.

Question 13

in relation to le chateliers principle, what happens when the pressure increases (decrease in volume)?

Answer 13

1. Increased pressure  system must decrease
   pressure to restore equilibrium.
2. To decrease pressure  system must reduce
   the moles of gas.
3. To reduce moles of gas  system must favour
   the reactant side of the reaction.
4. The equilibrium shifts to the left favouring the
   backward reaction.
5. The equilibrium constant is unchanged.

Question 14

What happens when we decrease the pressure
(increase volume) of the system?

Answer 14

1. Decreased pressure  system must increase
   pressure to restore equilibrium.
2. To increase pressure  system must increase
   the moles of gas.
3. To increase moles of gas  system must favour
   the product side of the reaction.
4. The equilibrium shifts to the right favouring the
   forward reaction.
5. The equilibrium constant is unchanged

Question 15

What affect does adding a catalyst make?

Answer 15

Adding a catalyst makes absolutely no difference
to the position of equilibrium, and Le Châtelier’s
principle does not apply.
* This is because a catalyst speeds up the forward
and back reaction to the same extent and adding
a catalyst does not affect the relative rates of the
two reactions, it cannot affect the position of
equilibrium.
*
Catalysts have some application to equilibrium
systems. - For a dynamic equilibrium to be set up, the
rates of the forward reaction and the back
reaction must be equal.
- This does not happen instantly and for very
slow reactions, it may take years!
- A catalyst speeds up the rate at which a
reaction reaches dynamic equilibrium

Question 16

What effects does addition and removal of species have in regards to Le Châtelier’s principle, specifically N2O4?

Answer 16

instantaneously alters the concentration of that species in the reaction mixture, provided that the reactant or product in question is not a pure solid or liquid. - the system is no longer at equilibrium

What happens when we increase the amount of
N2O4(g) in the system?
1. Increased N2O4(g) –> system must decrease
N2O4(g) to restore equilibrium.
2. To reduce the amount of N2O4(g) –> system
must favour the product side of the reaction.
{i.e. reacting away the excess N2O4(g)}
3. The equilibrium shifts to the right favouring the
forward reaction.
4. The equilibrium constant is unchanged.

What happens when we decrease the amount of
N2O4(g) in the system?

1. Decreased N2O4(g)  system must increase
   N2O4(g) to restore equilibrium.
2. To increase the amount of N2O4(g)  system
   must favour the reactant side of the reaction.
   {i.e. producing more N2O4(g)}
3. The equilibrium shifts to the left favouring the
   backward reaction.
4. The equilibrium constant is unchanged.

Question 17

What effects does addition and removal of species have in regards to Le Châtelier’s principle, specifically N2O4?

Answer 17

What happens when we add/remove a small amount of Ar(g) at constant volume?
1. Adding/Removing an inert gas at constant volume  increases overall pressure.
2. However, there will be no effect on the concentrations or the partial pressures of reactants or products.
3. The equilibrium does not shift.
4. The equilibrium constant is unchanged.

Question 18

What is the haber process, and explain the process in which it is commonly used?

Answer 18

The Haber Process is used in the manufacturing
of ammonia from nitrogen and hydrogen, and then
goes on to explain the reasons for the conditions
used in the process.

• The process combines nitrogen from the air with
  hydrogen derived mainly from natural gas
  (methane) into ammonia.
• The reaction is reversible and the production of
  ammonia is exothermic.

Question 19

What effect does temperature have on haber process?

Answer 19

reaction is exothermic –> lower temperature will increase the yield –> the slower the reaction becomes

400 - 450°C is a compromise temperature producing a
reasonably high proportion of ammonia in the equilibrium
mixture (even if it is only 15%), but in a very short time.

Question 20

What effect does Pressure have on haber process?

Answer 20

Product has less moles of gas –? higher pressure will increase the yield —> very high pressures are very expensive

200 atmospheres is a compromise pressure chosen on
economic grounds. If the pressure used is too high, the cost of
generating it exceeds the price you can get for the extra
ammonia produced.