3.1 Equilibrium Constant Flashcards
What is equilibrium?
moles of reactants and product are constant, rate of forward reaction = rate of reverse reaction
** dynamic - forward and reverse reactions still occur
What is the equilibrium constant?
relationship between pressures or concentrations of the reactants and products, K
What are equilibrium constants dependent on?
temperature
–> temperature change = equilibrium constant change
**effect is different depending on reaction is endo or exo and temp inc or dec
What is homogenous equilibrium?
all components are in the same phase
What is heterogenous equilibrium?
components are in different phases
Which components are considered for K value?
gaseous and not solid
What is the general form of equilibrium constant using concentrations?
K = [C]^c[D]^d/[A]^a[B]^b
Why are solid or solvent concentrations not considered for finding K value?
concentrations of solvent/solids are considered constant or equal to 1
How does the K value change when the reaction is reversed?
1/K
How does the K value change when the reaction is multiplied? divided?
K^(number multiplied)
ex. reaction x 2 = K^2
K^1/(number mutiplied)
ex. reaction x 3 = K^1/3
How does the K value change when you combine equilibria (add reactions)
K(new) = K1 x K2
What does it mean if K is greater than 1?
K=products/reactants
so: products>reactants
favours products = equilibrium lies towards the right/products side = at equilibrium, there are more products than reactants
What does it mean if K is less than 1?
K = products/reactants
so: reactants>products
favours reactants=equilibrium lies towards the left/reactants side = at equilibrium, there are more reactants than products
Why must only M (mol/L) and atm be used in K calculations?
equilibrium constants are actually given in terms of activity for species in a solution and fugacity for gas-phase species) which are related to concentration and partial pressure respectively, but don’t have units
– activity is approximated as concentrations in M units
– fugacity is approximated as partial pressure in atm
What is the reaction quotient?
same as equation equilibrium constant but allows for calculating whether the system is at equilibrium and what direction it needs to go to get to equilibrium
–> concentrations and partial pressures of reactants and products are not necessarily at equilibrium
What happens when Q = K?
Q>K?
Q<K?
Q=K –> system is at equilibrium
Q>K –> too many products - must shift left
Q<K –> too many reactants - must shift right
What happens to the equilibrium constant when temperature, pressure or reactant/products are added?
shifts position of equilibrium to a new value and the concentrations/pressures at equilibrium will be different
What is Le Chatelier’s Principle?
If a chemical system at equilibrium is disturbed by a change in temperature, pressure or the concentration of a participant in the equilibrium, the equilibrium will shift in such a way to minimize the disturbance
What is the impact of concentration change on equilibrium?
adding or removing reactants or products cause the reaction to shift left or right to reestablish equilibrium
What is the impact of total pressure change on equilibrium?
shift left or right: pressure of a species is directly proportional to the number ormolus of that species
How can the pressure of a system of gases be disturbed?
changing volume of system:
increasing volume = decrease pressure of each gas = reaction proceeds in the direction that produces more moles of gas to increase pressure again
decreasing volume = increase procession = reaction proceeds in direction that will produce fewer moles of gas
What occurs when an inert gas (one that doesn’t readily react) is added to gaseous equilibrium system?
increase in total pressure but no change in partial pressure of reactant and product gases = no change in equilibrium position
Does volume change impact only solid and liquid equilibriums (no gas)?
No
When does volume has no effect in a gaseous equilibrium system?
when number of moles is equal on both sides
Does K change when volume, concentrations or pressure is changed?
no! only temperature changes K value
How can enthalpy be written in a reaction?
endothermic = +∆H = reactant = heat/temp of surroundings decrease
exothermic = -∆H = product = heat/temp of surroundings increase
In an exothermic reaction what occurs when heat is added/temperature increased?
analogous to adding product:
equilibrium shifts left and produces more reactant, decreases K value
In an exothermic reaction what occurs when heat is removed/temperature decreased?
analogous to removing product:
equilibrium shift right and produces more product, increases K value
In an endothermic reaction what occurs when heat is added/temperature increased?
analogous to adding reactant:
equilibrium shift right and produces more product, increase K value (num)
In an endothermic reaction, what occurs when heat is removed/temperature decreased?
analogous to removing reactant:
equilibrium shift left and produces more reactant, decreases K value (denom)
What happens to equilibrium when ∆Gº is positive (>0)?
equilibrium lies to the left/reactant side and K is small
What happens to equilibrium when ∆Gº is negative (<0)?
equilibrium lies to the right/product side and K is large
What happens to equilibrium when ∆Gº = 0?
K = 1
What is the relationship between free energy under nonstandard and standard condition (∆G and ∆Gº)?
∆G = ∆Gº + R T lnQ
where Q is the reaction quotient
when Q = K at equilibrium and ∆G = 0:
∆Gº = -R T lnK
What is the relationship between ∆Gº and K?
∆Gº = - R T lnK
∆Gº = J/mol
R = 8.314 J/mol*K
T = 298.15 K
K = equilibrium constant
How can you find equilibrium constant at different temperatures?
lnK = -∆Hº/RT + ∆Sº/R
because enthalpy and entropy do not vary much over temperature range of reaction
What is van’t Hoff’s Equation? What is it used for?
determine K values at different temperatures or find temperature to carry out reaction for certain K:
lnK2/K1 = ∆Hº/R(1/T1 - 1/T2)
