Chapter 19 - Equilibrium Flashcards
What are the 2 main types of equilibria?
heterogeneous and homogeneous
What is heterogeneous equilibrium?
Equilibrium in which species making up the reactants and products are in different physical states
What is homogeneous equilibrium?
Equilibrium in which species making up the reactants and products are all in the same physical state
What is true about Kc and states?
Kc will only include terms for any gaseous and aqueous species, not solid
What is equilibrium concentration usually measured as?
moldm-3
How do you calculate the units for Kc or Kp?
Substitute the units into the expression and cancel out repeated units, and then record the units as the ones that have not be cancelled
Give the method for finding the equilibrium constant using experimental results
- Make a control using 20cm3 0.0500 moles of HCl
- Make a reaction mixture using 0.0500 moles of HCl, 0.100 moles of ethanol and 0.100 moles of glacial ethanoic acid with a total volume of 20cm3
- Put both in a fume cupboard for a week
- Empty the control into a 250cm3 conical flask, add 100cm3 of distilled water and add 2 drops of indicator (phenyl-aline)
- Titrate against a standard solution of sodium hydroxide
- Record the titre when there is a permanent pink colour change
- Repeat at least 3 times to gain 3 concordant results
- Repeat for reaction mixture
- Use the mean for each reaction as the equilibrium constant for that reaction
What are equilibria involving gases usually expressed as?
Kp - the equilibrium constant in terms of partial pressure
Under the same conditions of temperature and pressure the same ____ of different gases contain the same _____ ___ _____ of gas molecules
volume
number of moles
What is the mole fraction of a gas equal to?
Its proportion by volume to the total volume of gases in a mixture
How do you calculate the mole fraction of a gas?
dividing the number of moles of each gas by the total number of gas molecules.
How do you calculate the partial pressure of a gas without the mole fraction when given the total pressure and the pressure of 1 reactant
Use the total pressure- the partial pressure of the reactant and then divide that by the mole ratio
How is it best to display mole fractions?
As fractions
What should all the mole fractions add up to?
1
What should all the partial pressures add up to?
The total pressure
The sum of p(A), p(B), p(C) equals ….
P
As altitude increases what happens to atmospheric pressure?
It decreases
How does the body compensate for the decrease in atmospheric pressure at high altitude?
It produces more haemoglobin with a higher affinity for oxygen
How would the following equation be written as a Kp expression, when given the total pressure?
H2 (g) + I2 (g) <===> 2HI (g)
Kp = p(HI)2
p(H2) x p(I2)
How would the following equation be written as a Kc expression, when given the total volume ?
C (s) + H20 (g) <===> CO (g) + H2 (g)
Kc = [CO(g)] x [H2(g)]
[H2O (g)]
If the concentration of a species is increased what happens?
The position of equilibrium shifts in the direction that reduces the concentration
If the temperature of the reaction is increased what happens?
The position of equilibrium shifts in the endothermic side
What happens if the pressure of the reaction is increased?
The position of equilibrium shifts to the side that reduces the pressure (fewer gaseous molecules)
What phrase is used to show why the position of equilibrium moves?
TO OPPOSE THE CHANGE
If K =1 What is the position of equilibrium?
Halfway between the products and the reactants
If K >1 What is the position of equilibrium?
Towards the product side
If K<1 what is the position of equilibrium?
Towards the reactant side
The value of equilibrium constant will remain ____ _____ for any changes applied to the equilibrium system EXCEPT ______
the same
Temperature
When temperature increases in an endothermic forwards reaction what happens to the value of the equilibrium constant?
It increases
Explain why the value of Kp increases when the temperature increases in an endothermic forwards reaction
Kp increases and equilibrium shifts to the product side to resist the change.
RHS of the expression of Kp is now less than Kp because overall Kp has increased
This means the system is no longer in equilibrium
Partial pressures alter and give a new Kp
Explain why the value of Kp decreases when the temperature increases in an exothermic forwards reaction
Kp decreases and equilibrium shifts to the reactant side to resist the change.
LHS of the expression of Kp is now greater than Kp because overall Kp has decreased
This means the system is no longer in equilibrium
Partial pressures alter and give a new Kp
When temperature increases in an exothermic forwards reaction what happens to the value of the equilibrium constant?
It decreases
How can you work out if a reaction is exothermic or endothermic using the value of Kc under two different temperatures?
Compare the lower and higher temperature’s value for Kp. If the value for Kp is higher under higher temperatures than the reaction is endothermic
If the value for Kp is lower under higher temperature than the reaction is exothermic
How do catalysts affect equilibrium constants and why?
They do not affect equilibrium constants because the rates of both the forwards and reverse reaction are increased so the position of equilibrium remains unaffected
How do concentration changes affect the equilibrium constant?
No affect on equilibrium constant
How do pressure changes affect the equilibrium constant?
No affect on equilibrium constant
Why do concentration changes not affect the equilibrium constant?
Because:
If the concentration changes, the position of equilibrium will move to resist the change by going to the side with lower concentration. So the side with higher concentration now has a smaller value for Kp as the overall value has increased but that side has remained constant.
This means the system is no longer under equilibrium and the system adjusts itself to maintain the same equilibrium constant
Why do pressure changes not affect the equilibrium constant?
Because:
If the pressure changes, the position of equilibrium will move to resist the change by going to the side with fewer molecules. So the side with more molecules now has a smaller value for Kp as the overall value has increased but that side has remained constant.
This means the system is no longer under equilibrium and the system adjusts itself to maintain the same equilibrium constant
