equilibria

what is a reversible reaction

reactions that take place place in both forwards and revers directions

where are reversible reactions commonly found

industrial processes e.g. through harber process

what inidicates a reversible reaction

double arrow

what are the three conditions of dynamic equilibrium

-the rate of the forwards reaction is equal to the rate of the reverse reaction

2. concentrations of reactants and products do not change
3. to remain in equilibrium it must be a closed system

what may cause the position of equilibrium to change

temperature, pressure or concentration of reactants or products

What is Le Chatelier's principle?

when a system in dynamic equilibrium is subjected to an external change the system readjusts itself to minimise the effect of the change and restore eqilibirtum

what ions are used to measure the chnage of concentration in equilibrium

chromate and dichromate ions as it changes colour so its easy to see shifts in equilibrium

out of chromate and diochromate ions which are orange and which are yellow

chromate = yellow
dichromate = orange

what are the steps for the experiment using chromate and dichromate ions to test the principles of ewqilibium for concentration

1. add solution of yellow potassium chromate to beaker
   2.add dilute sulfruic acid until there is no furthercnage and the solution turns orange
2. add aqueous sodium hydroxide until there is no further chnage and the solution turns back to yellow

what happens when you add sulfuric acid to yellow potassium chromate and why

-increace concentration of H+ ions
-increaces the rate of the forward reaction
-causes the position of equilibrium to shift to minimus the change in H+ conc
-position of equilibrium shifts to the right side of reaction, making more products
-new position of equilibrium established towards products and solution turns orange as potassium dichromate forms

what happens when you add sodium hydroxifde to orange potassium dichromate and why

-when added OH- ion react with H+ ions which decreases the concentration of H+ ions
-shift increaces concentration of reacant that has been removed (H+)
-positon of equilibrium shifts to make more H+ ions
-new position of equilibrium established - yellow as CrO4 forms

what does the direction that eqilbirum moves depend on for temperature

depends on the sign of enthalpy chnage:
-forwward and backward reaction have the same value of enthalpy change but different signs
-increace in temp - shifts to endothermic reaction - (+)
-decreace in temp - shifts to exothermic reaction - (-)

what is an experiment used to test the principles of equilibrium for temperature

-colbablt chloride (pink to blue)
-experiment is sensitive to changes in temperature

what is the method used for the experiment testing the principles of equilibrium for temperature

1. dissolve cobalt chloride in water. add a small quantity of HCL.
2. place in ice water - solution turns pink
3. transfer into boiling water - solution turns blue

what are the results for the method used for the experiment testing the principles of equilibrium for temperature and why

-boiling tube Increaces the heat energy in a system
-as forward reaction is endothermic - position shists to right in endothermic direction - takes heat energy in. this minimises the increase in temp and turns the solution blue

• ice water decreaces the heat energy in a system
  -as backward reaction is exothermic - position shists to left in exothermic direction - releases heat energy. this maximises the increase in temp and turns the solution pink

what is the same as saying shifts in the forward reaction

-shits position of equilibrium to the right
-more products are made

what is the same as saying shifts in the backwards reaction

-shits position of equilibrium to the left
-more reactants made

what eqqulibirum reactions are affected by pressure

systems containing gases if there are more gaseous molecules on one side than the other

what colour is 2NO2 and what colour is N2O4

2NO2 - brown
N2O4 - colorless

what is pressure directly proportion and what does that mean

-pressure is directly proportional to concentration

• means that 2 mols of NO2 has twice the concentration and pressure than 1 mole of N2O4

what does increasing pressure in an equilibrium system do and why

-shifts position of equilibrium to the side with fewer mols in order to decreace the pressure of a system

what happens when pressure is isncreaced in 2NO2 -> N2O4

-fewer gasesous mols on right hand side - position of equilibrium shifts right - reducing pressure
-more N2O4 is produced so the brown colour fades

what happens when you add a catalyst to an eqilbirum system

-does not chnage the position of eqilbirum
-speeds up the rate of the forward and backward reaction equally
-increaces the rate that equilibrium is established

how is le chatillers principle involved in the haber process

-predicts the best temperature to force eqilbtium to the right to maximise the yield of 2NH3

what would thoretically be the best temperature for the haber process

-low temp and high pressure
-shifts eqilbium to the right

what would practically be the best temp for the harber process and why

• low temp produces high yield but very slowly - rate may be so slow that eqilbirum isn't even established
  -therefore needs to compromise conditions to give a reasonable rate without shift in the position of equilibrium (300-500)

what would practically be the best pressure for the harber process and why

-high pressure increaces yield but need to take into consideration the cost of the process (strong containers and large quantiles of energy) and possible satay concerns
-therefore compromiser of 100-200 atm is used - cheaper but still high yield

what is also used to lower cost in the haber process

-iron catalyst used to speed up rate of reaction so lower temp and operating costs
-also unreacted nitrogen and hydrogen are recycled repeatedly

what does equilibrium law calculate

the exact position of equilibrium

equation for eqilbirum constant

Kc = [C]^c [D]^d / [A]^a [B]^b

what does equilbrium constant tell us

the magnitude of the equilibrium constant indicates the relative proportions of reactants and products in the equilibrium system

what does it mean when Kc=1

indicates position of equilibrium that is halfway between reactants and products

what does it mean when Kc > 1

indicates position of equilibrium that is towards products

what does it mean when Kc < 1

indicates position of equilibrium that is towards reactants

the larger the Kc the….

further position of equilibrium lies to the right and the greater the conc of products compared to reactants

what are the two main types of equilibria

homogeneous and heterogeneous

what is homogenous equilibria

a reaction in which the catalyst and reactants are in the same physical state which is most frequently the aqueous or gaseous state

what is heterogenous equilibria

an equilibrium in which the species making up the reactants and products have different physical states

what are features of heterogenous equilibria and what does this mean when calculating Kc

-the conc of solids and liquids are essentially constant
-so any species that are solid or liquid are omitted from the Kc expression as they are automatically incorporated in the overall equilibrium constant

draw the rate of reaction graph for irreversible reactions for products and reactants

draw the rate of reaction graph for reversible reactions for products and reactants when the equilibrium favours products over reactants

draw the rate of reaction graph for reversible reactions for products and reactants when the equilibrium favours reactants over products

what is the ice method

an analysis of the initial chnage of equilibrium concentration
I - initial
C - change
E - equilibrium