topic 10+ 11: eqm 1 + 2 Flashcards
what is dynamic equilibrium
- forwards and backwards reactinos occur at equal rates
- concentrations of reactants and products remain constant
le chatelier’s principle
if a change happens the equilibrium will shift to try to reverse it
increase in temp effect on eqm?
- shifts equilibrium in the ENDOTHERMIC direction
difficulty with temp equilibrium
- low temperatures can give higher yield
- but slower rate
- so use a compromise temperature, OR LOW TEMP AND CATALYST
Effect of pressure on equilibrium
- causes equilibrium to shift to the side with FEWER MOLES OF gas
in industry, high temperatures and pressures are…
- EXPENSIVE (equipment and energy costs)
effect of concentration on equilibrium
- increase in concentration of one thing means the POE will shift in the opposite direction on this
effect of catalysts on equilibirum
NO EFFECT
- as speeds up rate of forwards and backwards reactions by same amount
- only speeds up rate at which equilibrium is achieved
advantage of using a catalyst?
- speeds up rate
- SO CAN USE LOWER TEMP AND PRESSURES
- lower energy costs
- lower equipment costs
strange way to increase yield?
- reversible reactions
- so recycle unreacted reactants
Kc expression
eg
A + 2B = 3C
Kc = [C]^3 / [A][B]^2
HOMOGENEOUS equilibirum
reactants and products all in same phase
heterogeneous equilibrium
reactants and products not all in same phase
in heterogeneous equilibrium, which do you include in Kc
GASES
- no solids or liquids
when do you include water in Kc
- when water is a REACTANT, not a solvent
- otherwise its concentration remains constant so isnt included
what can change Kc
ONLY THE TEMPERATURE!!!!!!!!
What does it mean in terms of products and reactants if Kc is large
- more products than reactants
- eqm lies very far to the right
which concentrations do you use in Kc
- the EQUILIBRIUM CONCENTRATIONS!!!!!!!
when calculating equilibrium concentration, which volume do you use
TOTAL REACTION MIXTURE volume
catalyst for preparing an ester with carboxylic acid and alcohol
dilute sulfuric acid
method for Kc experiment making an ester
- use burettes to measure amounts and mix together carboxylic acid, alcohol, dilute sulfuric acid catalyst. LEAVE FOR A WEEK TO REACH EQUILIBIRUM
- Rinse volumteric flask with water
- transfer reaction mixture in through funnel, rinse w distilled water and transfer washings in. make up to the mark. stopper, invert and shake
- use pipete to put 25cm3 of this into conical flask, and add indicator
- burette with alkali
- titrate
- SODIUM HYDROXIDE WILL REACT WITH THE CATALYST AND ANY UNREACTED CARBOXYLIC ACID
partial pressure of gas
mole fraction * total pressure
Kp only applies for
GASES
Value of K where reaction doesnt go
smaller than 10^10
reaction goes to ocmpleteion K
k > 10^10
delta S total
- entropy change of system + entropy change surrounding
- = RlnK
in industry is equilibirum ever reached?
NO
- products are removes as they are formed
- so not a CLOSED SYSTEM;
give 3 reasons why product may be removed before equilibrium is reached
- shifts POE to the right
- decreases rate of backwards reaction
- unreacted reactants can be recycled
2 ways to improve yeild industrially (2)
- recycle unreacted products
- remove product as its formed
state and expain one benefit to the environment resulting from use of catalysts in industry (2)
- lower temp needed
- less combustion of fuels, so fewer harmful emissions eg co2 ghgs
if titre the same , what feature of equilibrium displayed?
- forwards and backwards reactions at same rate
- conc products and reactants remain constant
suggest why test tubes are sealed
- prevent evaporation
why no need to have volume for this calc? (2)
- equal moles products and reactants
- VOLUMES CANCEL
why might a mixture lef tto sit go acidic?
absorbs CO2 from atmosphere
how would you confirm a week is long enough to reach equilibiru ? (2)
- repeat exp and leave LONGER THAN A WEAK
- titrate, titre should be the same
haxard of hydrogen
flammable
why not include solid in Kc
conc is constant
why not include solid in Kp
solid doesnt exert pressure / presure is constant
why might increasing pressure NOT affect rate(catalyst ) (2)
- reaction occurs on surface of catalyst
- active sites saturated with reactants
delta s total =
RlnK
