7. dynamic equilibrium

Question 1

what is dynamic equilibrium

Answer 1

1. as reactants get used up forward reaction slows down and as more product is formed reverse reaction speeds up
2. in time forward react and backward reaction same rate = amount of reactants and products wont change

Question 2

a dynamic equilibrium can only happen in a

Answer 2

closed system (nothing can get in or out)

Question 3

things that can alter position of equilibrium

Answer 3

temperature
concentration
presssure

Question 4

le chateliers principle states

Answer 4

if theres a change in concentration, pressure or temperature the equilibrium will move to help counteract the change

Question 5

increased concentration of reactant

Answer 5

1. increased concentration of reactant, equilibrium tries to get rid of extra reactant = makes more product. equilibrium shifted to right

Question 6

increased concentration of product

Answer 6

increased concentration of product, equilibrium tries to remove extra product = reverse reaction faster, equilibrium shifts to left

Question 7

change in pressure only affects

Answer 7

gases

Question 8

increase in pressure

Answer 8

shifts equilibrium to side with fewer gas molecules = reduced pressure

Question 9

decrease in pressure

Answer 9

shifts equilibrium to side with more gas molecules = increased pressure

Question 10

increased temperature (adding heat)

Answer 10

equilibrium shifts in endothermic direction (+ delta H)

to absorb heat

Question 11

increase temperature (removing heat)

Answer 11

equilibrium shift in exothermic direction (-ve delta H)

to replace heat

Question 12

do catalysts affect position of equilibrium

Answer 12

no.

they speed up forward AND reverse reaction by same amount.

Question 13

do catalysts increase yield

Answer 13

no but they mean equilibrium is reached faster

Question 14

how is industrialproduction of ethanol a good example of how le chateliers principle is important

Answer 14

ethanol is produced via a reversible ecothermic reaction between ethene and steam
reaction carried out at pressure of 60-70 atmosphers and temperature of 300 C with a phosphoric (V) acid catalyst

Question 15

how is the production of ethanol from steam and ethene a good example of conditions chosen for compromise

C2H4(g) + H2O(g) C2H5OH(g) delta H=-46kJmol-1
300 C
60-70 atm
(phosphoric (V) acid catalyst)

Answer 15

exothermic reaction = lower temperature favour forward reaction = better yield
HOWEVER
low temperature = slower rate of reaction
300 C compromise between max yield and faster reaction

high pressure favours forward reaction
pressure of 60-70 atm = high pressure moves reaction to side with fewer gas molecule
increased pressure also increases rate of reaction.
high pressure expensive to produce need stronger pipes/ containers.
60-70 atmospheres compromise between maximum yield and expense

ALL COMES DOWN TO MINIMISING COST