chemical equilibria Flashcards
how is it often denoted that a reaction is reversible
using a double headed arrow
where can an equilibrium only be established
in a closed system
where can equilibrium be set up from
either direction
what is reached at equilibrium
a natural balance between products and reactants
why are chemical equilibria dynamic
both the forward and reverse reactions continue to occur
rate of forward reaction equals…
rate of reverse reaction
the concentrations of reactants and products remain constant unless…
the conditions are changed
what can changes to the conditions of an equilibrium affect
the position of the equilibrium
le chateliers principle
if a system in equilibrium is subjected to change, the position of the equilibrium will move in the direction which opposes that change
when will the equilibrium shift to the right
if the conc of reactant is increased/conc of product decreased
when will the equilibrium shift to the left
if the conc of reactant in decreased/conc of product increased
which side does the equilibrium shift to if the total pressure is increased
to the side with fewer moles of gas because fewer moles of gas exert less pressure
which side does the equilibrium shift to if the total pressure is decreased
to the side with more moles of gas because more moles of gas exert more pressure
what effect does an increase in pressure have on the rate of reaction
increases rate of reaction
why does increased pressure increase rate of reaction
collisions between molecules are more frequent
which direction will the equilibrium move in if the temp is increased
the direction of the endothermic reaction (TAKES HEAT IN)
which direction will the equilibrium move in if the temperature is decreased
the direction of the exothermic reaction (GIVES OUT HEAT)
what does the way the equilibrium responds to change in temperature depend on
whether the forward reaction is exothermic or endothermic
what does an increase in temperature always increase
the rate of the forward and backward reactions but to different extents
what does a catalyst increase the rate of the forward and backward reactions by
the same amount
what effect does a catalyst have on the equilibrium position/yield
none
what does using a catalyst increase
the rate at which the equilibrium position is reached
the haber process
N2(g)+3H2(g)> 2NH3 (g)
what is dependent on the conditions used in the haber process
the equilibrium position, yield of ammonia and rate of reaction
what are used in order to balance yield of ammonia, rate of ammonia production and energy requirements
a compromise temperature and pressure
what pressure is the haber process conducted under
200 atm
what temperature is the haber process conducted under
400-450 degrees celcius
what catalyst is used in the haber process
iron
what is also used in the haber process
recycling
what is Kc
the equilibrium constant in terms of the concentrations of the reactants and products
Kc=
aA + bB >< cC + dD
(C)c(D)d- PRODUCTS/(A)a(B)b- REACTANTS
what are (A) (B) (C) (D)
the concentrations of the reactants and products at equilibrium
what are a b c and d
the stoichiometric coefficients of the balanced equation (moles)
what does the value of Kc indicate
the extent of the reaction
what does it mean if Kc is less than one
there are more reactants than products, equilibrium lies to left hand side
what does it mean if Kc is equal to one
reactants = products
what does it mean if Kc is greater than one
there are more products than reactants so the equilibrium lies to the left hand side
what do the units for Kc depend on
the reaction, must be determined for each Kc expression
does the presence of a catalyst or change in concentration affect Kc
no
what does affect Kc
change in temperature
what will happen to Kc if the temperature change causes the equilibrium to shift right
Kc will increase
what will happen to Kc if temperature change causes equilibrium to shift left
Kc will decrease
what will there be a mixture of when a reversible reaction has reached equilibrium
reactants and products
what can the amount of each chemical present at equilibrium be determined by
the balanced equation and the initial moles
