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
