19 - Equilibrium Flashcards
Homogenous equilibria
contains equilibrium species that all have same state/phase.
Heterogenous equilibria
contains species that have different states or phases.
what do you not include in kc expression
any species that are solid or liquid
what do you include in kc expression
species that are (g) or (aq)
how to find kc
1 - make a race table to find equilibrium moles
2 - use n=cv to find equilibrium CONCENTRATION
3 - then use Kc formula
how to get Kc experimentally - whole method
mole fraction
fraction of the total number of moles that each chemical in a reaction is responsible for
write kc expression for N2 + 3H2 -> 2NH3 (reversible)
what is partial pressure
contribution that the gas makes towards the total pressure
the pressure that would be exerted by a gas in a mixture of gases if it occupied the same volume on its own at the same temperature
sum of partial pressures
- Sum of partial pressures of each gas equals total pressure.
sum of mole fractions
1
how to find partial pressure
total pressure X mole fraction
what is kp
- like Kc but partial pressure replace concentration
units of partial pressure
kPa / Pa / atm
how to calculate kp from heterogeneous equilibrium
only use gaseous species
effect on kc / kp if you increase temp on an exothermic reaction, in forward direction
- if temp increases kp decreases
- kp expression / ratio of products : reactants is now greater then kp
- so we need to lower the fraction
- decrease numerator - decrease products + increase denominator - increase reactants
- shifts towards left
- equilibrium reached is now equal to new kp
effect on kc if increase temp on an endothermic reaction, in forward direction
- if temp increases kp increases
- kp expression / ratio of products : reactants is now less then kp
- so we need to increase the fraction
- increase numerator - increase products + decrease denominator - decrease reactants
- shifts towards right
- equilibrium reached is now equal to new kp
changes in conc and pressure on kc
- Value of equilibrium constant K is unaffected by changes in concentration/pressure.
- Equilibrium shift changes and results from the fact that equilibrium constant doesn’t change.
what happens if increase conc of reactants (LHS)
- denominator of kc / kp expression larger
- kc / kp itself does not change
- ratio of products: reactants is less than kc
- to return back to normal - increase fraction
- increase numerator - increase products + decrease denominator - decrease reactants
- shifts to right
effect of catalyst on equilibrium
speeds up both forward and reverse reactions in equilibrium by same factor
Equilibrium is reached quicker but position is not changed.
how would you work out the units of kp
the same way you work out the units of kp
how could the amount of iodine be determined in this reaction
2HI (g) -> H2 (g) + I2 (g)
A colorimeter could be calibrated using known concentrations of iodine vapour.
The concentration of iodine in the equilibrium mixture could then be determined
where do you put the ‘p’ in the kp formula
inside the bracket - check mark schemes
how would you calculate the total pressure of a system using kp
calculate the amount of moles of each component at equilibrium
calculate mole fractions
calculate partial pressures of each component in term os total pressure (P)
substitute into kp formulla
