Chapter 10 - Chemical equilibrium (L) Flashcards
What is chemical equilibrium?
When the forward and backwards reactions are occurring at equal rates
What 2 things must the reaction be for equilibrium to be reached?
- The reaction must be closed (i.e. nothing being added or removed)
- The reaction must be reversible
What is Le Chatelier’s principle?
If a reaction is at equilibrium, and the reaction conditions are then changed, the equilibrium position will shift in the direction that opposes the applied change
What are the 3 changes that affect position of equilibrium?
- Pressure
- Temperature
- Concentration of reactants/products (material either added or removed)
What is the effect on equilibrium position when reactants are added?
Shifts to right to get rid of added reactants
What is the effect on equilibrium position when reactants are removed?
Shifts to left to produce more reactants
What is the effect on equilibrium position when product is added?
Shifts to left to get rid of added product
What is the effect on equilibrium position when product is removed?
Shifts to the right to produce more product
When do changes in pressure affect the position of the equilibrium?
For reactions that involve gases
What is the effect on equilibrium position when the temperature is increased on a forward exothermic reaction?
The equilibrium will move to the left (in the endothermic backwards direction) to lower the temperature
What is the effect on equilibrium position when the temperature is decreased on a forward exothermic reaction?
The equilibrium will move to the right (in the exothermic forward direction) to increase the temperature
What is the effect on equilibrium position when the pressure is increased?
The equilibrium will shift to the side with the fewer moles of gas to lower the pressure
What is the effect on equilibrium position when the pressure is decreased?
The equilibrium will shift to the side with more moles of gas
What is the effect on equilibrium position when the pressure is decreased?
The equilibrium will shift to the side with more moles of gas
What is the effect on equilibrium position when a catalyst is added?
There is no effect on the position of the equilibrium
What happens when a catalyst is added to a reaction in dynamic equilibrium?
The speed of both the forward and backwards reactions increase- it helps the reactions form equilibrium faster
What are heterogenous systems?
A system in which there are at least two different states present (e.g. gas + solid or liquid + aq)
What are homogenous systems?
A system in which all components are the same state
What factors affect the equilibrium constant?
The value of the equilibrium constant only changes if temperature changes- other changes e.g. pressure do not change the value
What is the symbol for the value of equilibrium constant?
Kc
In equilibrium law, what do the lower case letters represent?
The number of moles of the substance
e.g. 6H2O
The 6 would be the lower case
In equilibrium law, what do the upper case letters represent?
The concentration of a given substance in the reaction
e.g. 6H2O
The 6 would be the lower case, and the concentration of H2O would be the upper case
What is the formula for Equilibrium law i.e how do you work out Kc?
Kc =
[C]^c [D]^d
–––––––––
[A]^a [B]^b
When Kc is significantly greater than 1, what does this indicate?
More product made than reactant
When Kc is around 1, what does this indicate?
The amount of product made is roughly equal to the amount of reactant made
When Kc is significantly less than 1, what does this indicate?
Very little product made- reaction barely starts
What do you do with solids and liquids in equilibrium law and why?
You leave them out because their concentrations are constant/unchanging
What the chemical equation for the manufacture of ammonia?
N2+ 3H2 - 2NH3
What is the process used for manufacture of ammonia called?
The Haber process
Which direction of the Haber process exothermic?
The forward reaction is exothermic
What are the typical conditions of the Haber process?
450 degrees C and 250 atmospheres
Why is a temperature of 450C used in the Haber process?
Too low of a temperature will mean the rate of reaction is too slow, and the catalyst will not be able to function efficiently
Too high of a temperature would be uneconomical due to energy costs, and may also result in a decreased ammonia yield (as the forward reaction is exothermic)
So a compromise temperature of 450C is used.
Why will an increased pressure increase ammonia yield in the Haber process?
Because there is fewer moles of gas on the right than the left, so the equilibrium will shift to the products side with an increased pressure
Why is a pressure of 250atm used in the Haber process?
The higher the pressure, the higher the ammonia yield, but also the higher the cost. So a compromise pressure of 250atm is used.
What type of catalyst is most commonly used in industry for the Haber process?
An iron catalyst, as it is the cheapest
What process is sulfuric acid manufactured by?
The Contact process
Why is a temperature of 450C used in the Contact process?
For the same reasons as the Haber process-
too high = expensive and lower yield (due to exothermic forward reaction)
too low = slow rate of reaction + catalyst cannot work efficiently
In the Contact process, what direction is endothermic?
Backwards
What is the chemical formula for the production of sulfur trioxide in the Contact process?
SO2 + 1/2O2 - SO3
What catalyst is used in the Contact process?
Solid vanadium oxide
Why is a pressure of 2atm used in the Contact process?
Although in this reaction higher pressures = higher yields (as there are fewer moles on the right), at an atmosphere of just 1, the yield is already 97%. Therefore a pressure of 2atm is used, as any pressure higher than this would be unnecessary and a waste of money
