Equilibrium Flashcards
chemical equilibrium
state where the forward reaction rate(rf) is equal to the reverse reaction rate(rr)
dynamic equilibria
there is constant movement and each species is actively consumed and actively formed
criteria for a system to be in equilibrium
- constant macroscopic properties
- closed system
- shift in response to changes
macroscopic property
property observed with the naked eye
criteria: macroscopic properties
should have constant concentrations, pH, color, and temperature
closed system
a system where chemicals do not enter or leave
steady state
system that appears to be at equilibrium but chemicals are entering and leaving the system at the same time
criteria: shift in response
a change(stress) causes the system to respond
equilibrium stages: 1
reactant concentrations are high, rf is at the highest
equilibrium stages: 2
[A] and [B] and rf decreases
[C] and [D] and rr increases
equilibrium stages: 3
[A] [B] [C] [D] are constant and rr and rf are equal
Le Chatlier’s principle
an equilibrium when subjected to stress will shift to alleviate the stress
stress
any change that favors rf or rr
stress: change in concentration
if the concentration of a chemical species increases, then the system will shift to consume that species; if the concentration decreases, the system will shift to produce that species
shift right
when a system shifts to favor the products
shift left
when a system shifts to favor the reactants
adding a catalyst
does not affect equilibrium, but systems will alleviate the stresses applied faster
equilibrium position
relative concentrations of chemical species in equilibrium expressed in percent yield
shift right
if the percent yield is above 50%
shift left
if the percent yield is less than 50%
partial pressure
pressure exerted by an individual gas in a mixture
partial pressure is to gaseous equilibria as
osmotic pressure is to solution equilibria
gas pressure is directly proportional to gas concentration and
osmotic pressure is directly proportional to solution concentration
stress: change in volume
the side of equilibrium with the greater sum of coefficients will be more sensitive to volume change
stress: change in temperature
a system in equilibrium will shift to replace lost kinetic energy or shift to remove added kinetic energy
a system in equilibria will shift
before the stress is fully applied
when heat is added
the endothermic direction is favored
Haber Bosch Reaction
N2 +3H2 -> 2NH3 +92.4 kJ
haber reactor pressure
increased to 3.5 x 10^4 kPa
equilibrium expression
formula for finding the equilibrium constant in terms of concentrations of products and reactants
equilibrium constant(keq)
numerical value that related the concentrations of products to the concentration of reactants in equilibria
keq requirements
-units vary and are not required to be expressed
-temperature dependent
products are favored, shift right
keq > 1
reactants are favored, shift left
keq < 1
equilibrium law
the expression of a balanced chemical equation and an equilibrium expression together
reaction quotient(Q or trial keq)
numerical value calculated from taking any set of concentrations and plugging them into an equilibrium expression
shift left
Q>Keq
shift right
Q<Keq
exception to le chatelier
if only one chemical species is present in an equilibrium expression, the system will shift to completely alleviate a stress that affects its concentration
ICE Box
table that is used to solve calculations in systems of equilibria where ICE is an acronym
-concentrations needs to be in molarity
-pay attention to the coefficients
mass action expression
equilibrium expressions in terms of concentration or partial pressure
14.7 psi
psi in atm
760 mmHg
mmHg in atm
Kp=
Kc(RT)^(delta n)
delta n=
(c+d)-(a+b)
ideal gas law constant(R)
0.08206 (L x atm)/(mol x K)
