Chem (Equlibrium) Flashcards
Equilbria is a state of..?
balance- the forward and backward reactions are going at the same rate- concentration is constant
Dynamic equlibrium is..?
backward and forward reactons are going at the same rate at a constant concentration
e.g. oxyhemoglobin into tissues and back
Equlibrium can only eb reached in a ..?
closed system- no material exchanged with the surroundings- loss of reactants/products
Le chatelier’s principle is..?
If a change is imposed on a system of eqilbrium the system will act to minimise that imposed change
Changing the temperature will..?
exothermic/endothermic reaction?
rate of reaction?
increase temp
shift the eqilbrium in the endothermic direction to aborb energy -cool it down if the reaction is exothermic
shifts to the left > reduces the yield
decrease temp-shifts towards the right- oppositie direction
endothermic reactions everything’s opposite
If you increase the overall pressure.. ?
moles on both side equal?
no change if moles same on bot sides- no effect on equilbiru position
Increasing the cocentration (of the reactants obviously)..?
increase concentration of products?
The equilbrium will shift to the right to make more product (forwrd direction) > increase yield.
move to the left>decrease yield (backward direction)
Catalysts do not have an effect on the equilbrium- they only spped up the..?
rate of reaction
Why hgih pressures are not used in industry like the harber process?
-high pressure equipment like pressure tanks/high cost of it
Ethanol: C2H4 + H20> C2H50H [-45 kjmol-1)
optimum condtions?/ catalyst?
Why do you use only 1 volume of H20 : 1:5 volumes of ethene to make ethanol?
optimum- temp of 573K
catalyst- spped up rate of reaction
make sense to add stea- H20 is cheap but
because phosphoric acid catalyst is soluble in water/too much can wash the catalyst off
Lower temperature would imcrease yield as..
but compromsie of 573K as..?
it would shift in the exothermic direction > right to heat it back up > increase yield
BUT would slow rate of reaction down too much for industry
compromise temperature
6000-7000 kpa is used instead of an even higher pressure to get an even higher yeild as..
More moles on reactant sde> shifts to right to increase on product side>increases yield
ethene plymerises at high temp/pressure to form poly(ethene) which clogs inside of vessel (expensive to maintain)- compromsie
pressure
continued recyking of ethene and steam- 5% conversion rate to 95% conversion rate (products)
For methanol production
step 1- CH4 + H20 > C0 + 3H2
hjigh temp..?
Temperatre of 1123 K- high because it increases yield AND rate of reaction.
Because this is endothermic- increasing temp shift it in the exothermic direction> to the left > increase yield as it trys to cool down
Why do you use a fairly high compromise pressure of 3000Kpa
conversion rate?
More moles on product side>high pressure > shift towards left to increase on reactant side
Low pressure increases required pridcuts in mixture but small overall yield since low pressure means few reactants
Cost-effective/overal prioductivity- compromise of a fairly high yield
90%
Why do you use a nickel catalyst in methanol production?
shortens the time to reach equilbrium
CO + 2H2 > CH30H (methanol)- where does the extra hydrogen go?
The extra hydrogen reacts with added C02 to make more methanol and H20
Why do we use a fairly high temperature of..?
523K
-because high temp>shift in left(endothermic) direction>towards reactants>decrease yeild
BUT it increases rate of reaction
Why do we use a compromise pressure of..
5000-10000 Kpa
becuase less moles on product side so shift to right (exotheric direction) > increas yield
High-energy costs in pressure equpment means compriomise temperaure (not too high)
catalyst of copper and?
zinc oxide
combustion og methanolo and ethanol reuslts in?
C02 emissionsbut no hydrocarbon emissions
methano isn’t carbon netural as..
fossil fuels?
converts carbon from fossil fuels so burns o produce C02 in engines
Howver methane can be produced from?
fermentation
decaying plant material (respiresd anaerbically) > carbon is recyled in steam reforming process (carbon neutral)
