equilibria Flashcards
define Le Chatelier principle
equilibrium will shift to opose any change
what are features of dynamic equilibria
-the rate of the forward and backward reaction are equal
-the concentration of products and recatants remain constant
explain the effect of changing the concentration on the position of equilibrium
if you increase the concentration of the reactants. equilibrium will shift to the rhs to oppose the change and yield of products will increase
however if you decrease the concentration of reactants. equilibria will shift to the lhs to oppose the the change and yield of reactants will increase
same applies for the products
explain the effect of change in pressure on equilibrium
pressure only affects the position og equilibrium that involve gases
if total pressure is increases the equilibria moves to the side with fewer gas moles to oppsode the chsnge
if total pressure is decreased then equilibria shuifts to the side with more gas moles
when the moles of gas are the same on both sides it has no effect on equilibruia
explain the change temperature has on equilibria
-if we increase temp
-equilibrium will shift to decrease the temp
-so shifts in the endothermic way
if we decrease temp
-equilibrium will shift to increase temp
-so shifts in the exothermic way
explain why a catalyst has no effect on equilibrium
catalyst has no effect on the yield as it increases the rate of both the forward and backward reactions equally
pros and cons of each condition in industrial processes
increase pressure
/can increase the yield
/can be faster
x can be more expensive
decrease temp
/higher yield
/cheaper
x slower
catalyst
/faster rate
/cheap
x doesnt increase yield
expression for kc
kc = products /reactants
CH4 +H2O <—> CO +3H2 AH=+206 KJmol-1
use le chateliers principle to state whether a high or low temp should be used to obtain the highest possible equilibrium yield of hydrogen from this first stage
-high temperature
-the forward reaction is endothermic so absorbs heat
-so if you increase temp, EQ will shift to oppose the chnage and abosrb the energy so temp is cooled
le chateliers principle suggests that a high pressure will produce a low yield of hydrogen in the 1st stage
explain why a high operating pressure is used in industry
-high pressure means more successful collisions in a given time
- so faster rate of reaction
a nickel catalyst is used in the first stage
explain why the catalyst is more ffective when coated onto an unreactive honeycomb
-increases surface area
-so increases rate of reaction as theres a higher frequency of successful collisions
H2C=CH2+H2O <—> CH3CH2OH AH=-42KJmol-1
the operating conditions for the process are temperature of 300°C and a pressure of 7 MPa, under these conditions the conversion of ethene is 5%.
identify the catalyst used in this process. deduce how an overall yield of 95% is achieved in this process without changing the operating conditions
catalyst: conc H2SO4
and the overall yield is is achieved by recycling the unreacted ethene
explain why a manufacturer might consider using an excess of steam in this process, under the same operating conditions
-there are more moles on the LHS so if you have an excess of steam EQ will shift to the right to oppose the change. so yield will increase as its a forward reaction
at pressures higher than 7MPa, some of the ethene reacts to form a solid with a relative molecular mass greater than 5000
deduce the identity of this solid.
give one other reason for not operating this process at pressures higher than 7MPa
-polyethene
-too expensive, as at higher pressures more expensive equipment is used
