physical chem; chemical equilibria, le chatliers principle & Kc Flashcards
what is a reversible reaction?
it’s a reaction that allows products to react to reform their original reactants
explain how the forward reaction is shown on the conc/time graph
initially reactants are used up quickly but then slow down as their conc drops
explain how the backwards reaction is shown on the conc/time graph
initially reactants are reformed slowly but the speed up as the conc of products increases
define dynamic equilibrium
the rate of the forward reaction is the same as the rate of the backwards reaction in a closed system & the conc of products & reactants are the same
what is a closed system?
none of reactants/products escape from reaction mixture
what is an open system?
matter & energy can be lost to the surroundings
how can equilibrium be reached in a solution?
can be reached in an open flask as amounts of material can be lost through evaporation
how can equilibrium be reached for gases?
only in a closed system
what is le chatlier’s principle?
if a reaction at equilibrium is subjected to a change in pressure, temperature or concentration, the position of equilibrium will shifts to counteract that change
what are the effects of changes on conc on the position of equilibrium?
increased conc of reactant = shifts to the right to use it up & reduce its conc (more product produced)
increased conc of products = shifts to the left to use it up & reduce the conc (more reactants produced)
define homogeneous equilibria
this is where reactants & products in the same state
what are the effects of changes in pressure on the position of equilibrium?
increased pressure = shifts to side with fewest no.of gas particles
decreased pressure = equilibrium will shift to the side with the most no.of moles
what are the effects of changes in temperature on the position of equilibrium?
increased temp = shifts in the endo direction to reduce the temp
decreased temp = shifts in the exo direction to increase the temp
state the effects of catalysts on the position of equilibrium
no effect as catalysts will speed up the rate of the forward & backward reaction equally
what effect do catalysts have on yield?
none, a catalyst will speed up the rate at which equilibrium is reached & has no effect on yield
what are the conditions for making ethanol?
pressure = 60 atmospheres
temp = 300°
catalyst = phosphoric acid (H₃PO₄)
explain the process of making ethanol by adjusting the temperature, referring to le chatelier’s principle
forward reaction is exothermic so decreasing the temp means equilibrium shifts to the right producing more ethanol
state the limitation of adjusting the temperature to produce more ethanol
as the temp is lowered the rate is lowered as well
explain the process of making ethanol by adjusting the pressure, referring to le chatelier’s principle
high pressure increases rate
high pressure & fewer no.of moles on the right means equilibrium would shift to the right producing more ethanol
state the limitation of adjusting the pressure to produce more ethanol
high pressure environments are expensive
how does temperature affect Kc?
Kc is only valid for 1 temp
changing the temperature will change equilibrium concs so Kc will change too
how does temperature change affect the value of Kc in an equilibrium?
if temp change causes equilibrium to shift right Kc will increase
if temp change causes equilibrium to shift left Kc will decrease
how does concentration affect Kc?
value of Kc is unaffected by any changes in conc
how do catalysts affect Kc?
no effect on the value of Kc as catalysts speed up the forward & backwards reaction equally
