Equilibrium Law and Chemical Equilibrium Flashcards
Gibbs free energy and Equilibrium, what is ∆G?
Predicts if the reaction is spontaneous or not (at constant T and P
∆G equation:
∆G = ∑∆Gf⁰(products) - ∑∆Gf⁰(reactants)
For the reaction to happen…
For the reaction: R→ P 1 mol of R reacts to form 1 mol P
G decreases as the reaction proceeds
2H2(g) + O2(g) → 2H2O(l) what is G energy? decrease or increase?
This reaction goes to completion where the lowest G energy is achieve
to show equilibrium:
For the reaction: R ⇋ P 1 mol of R reacts to form observable amounts of R and P
G decreases as the reaction proceeds
∆G = ∑∆Gf⁰(products) - ∑∆Gf⁰(reactants)
E (equilibrium): G has reached minimum, G
increases beyond this and is non-spontaneous
The composition of the reaction mixture does not change beyond E – the equilibrium composition of the reaction mixture
“A system comes to equilibrium when it reaches its minimum Gibbs energy.”
Applies to changes at Constant T and P
Reverse reaction: start with 100% P, decrease in G until point E
Define dynamic equilibrium:
reactions do not stop when equilibrium is reached. The forward and backwards reactions continue to occur at the same rate. The overall proportion of R and P does not change.
Thermodynamic Equilibrium Constant K
Describes the composition of a reaction mixture when it comes to equilibrium
k is the ratio between…
the products and reactants in a reaction scheme
Kc=
Kc= [C]^c [D]^d / [A]^a [B]^b
Gas-phase Reactions:
Kp - used in reaction incl. only gas
Kp = PC^c PD^d / PA^a P B^b
How set to up a Kp equation;
depends on how many moles of each molecule/compound
Acid / Base Dissociation Constants:
Ka = [H+] [A-] / [HA]
Thermodynamic Equilibrium constant (K) = Standard Equilibrium Constant KӨ
“Ratio of the thermodynamic activities of the products at equilibrium to those of reactants, considering stoichiometry”
Define Thermodynamic Activity:
Effective measured concentration or pressure of a component at a given moment (equilibrium for K)
What is unit of K
No units - its dimensionless
When is K used?
Heterogeneous reactions – more than one phase
Instead of using KC or KP, K is used
K must always be associated with a specified ________ and the equation of the reaction being considered
temprature
The Reaction Quotient Q
Measure of the composition of the reaction mixture as the reaction progresses – not at equilibrium
What do each letter of the equation mean?
K = thermodynamic equilibrium constant
pi symbol = product of (combined)
a products = equilibrium activities of the products
a reactants = equilibrium activities of the reactants
eqm Vp = stoichiometry of the products
eqm Vr = stoichiometry of the reactants
Q = pi (a(produts))^Vp / pi(a(reactants))^Vr
Why use Q =
Of its not on the equilibrium point exactly it is Q
K is the EXACT point of equilibrium
Q used at the point before equilibrium or beyond equilibrium
Determine results of reaction:
If ∆Gr < 0, Q < K then the forward reaction proceed
If ∆Gr > 0, Q > K then the reverse reaction proceeds
If ∆Gr = 0, Q = K then the system is at equilibrium
Equilibrium ______ when Gibbs energy is at its minimum (constant T and P).
reached
The Equilibrium Constant (K) measures pressures (or concentrations)
Therefore, there is a quantitative relationship between ___ and _
∆G and K
∆rG = -RT ln K
∆rG = standard Gibbs energy change
R = Gas constant (8.314jK^-1 mol ^-1)
T = temperature (K)
ln = natural logarithm
K = Thermodynamic equilibrium constant
By rearranging this equation, the K value can also be calculated:
K = e(-∆Gr/RT)
“ex” is the exponential function. e has a specific value =
2.718
K gives information about the _______ of the reaction mixture at equilibrium
composition
How K effects…
K > 1: Mainly P and therefore –ve ∆G (ln of numbers >1 are +ve)
K < 1: Mainly R formed and +ve ∆G (ln of numbers 0<x<1 are –ve)
K = 1: Equal amounts of P and R and ∆G is zero
When R <>P
If ∆Gr more –ve than -22.8 kJ/mol, reaction goes to completion
If ∆Gr more +ve than +22.8 kJ/mol, reaction does not occur
Complete reaction is 99.99% P formed
What is Le Chatelier’s Principle?
“When a change is made to a system in dynamic equilibrium, the system responds to minimise the effect of the change.”
P and T effect a reaction because they influence the K and ∆Gr and hence the position of the equilibrium
Effect of change in pressure:
N2O4 (g) <> 2NO2 (g)
If K is constant and Ptotal changes, then the mole fraction must change to compensate
Increasing P will move equilibrium to the left in this example as there are fewer moles of gas on the left.
This reduces the impact of increasing pressure
Changing number of components;
N2(g)+ 3H2 <> 2NH3 (g)
NH3 added to system will N2 and H2 increase of decrease?
Increase
ICE table
initial
change
equilibrium
Whta is importnat to remember in the ICE table?
RATIO of profucts and reactants
If change in reactant goes down/up….
products will do the opposite (as they have to balance)
ΔG = ΔH − TΔS
If ∆H and ∆S are independent of temperature, then ∆S/R is constant
2 equations of ln K
ln K = contstant ΔH / R (1/T)
ln K = ∆rS/ R - ∆rH/ RT
