Equilibrium Law and Chemical Equilibrium

Question 1

Gibbs free energy and Equilibrium, what is ∆G?

Answer 1

Predicts if the reaction is spontaneous or not (at constant T and P

Question 2

∆G equation:

Answer 2

∆G = ∑∆Gf⁰(products) - ∑∆Gf⁰(reactants)

Question 3

For the reaction to happen…

Answer 3

For the reaction: R→ P 1 mol of R reacts to form 1 mol P
G decreases as the reaction proceeds

Question 4

2H2(g) + O2(g) → 2H2O(l) what is G energy? decrease or increase?

Answer 4

This reaction goes to completion where the lowest G energy is achieve

Question 5

to show equilibrium:

Answer 5

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

Question 6

“A system comes to equilibrium when it reaches its minimum Gibbs energy.”

Answer 6

Applies to changes at Constant T and P
Reverse reaction: start with 100% P, decrease in G until point E

Question 7

Define dynamic equilibrium:

Answer 7

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.

Question 8

Thermodynamic Equilibrium Constant K

Answer 8

Describes the composition of a reaction mixture when it comes to equilibrium

Question 9

k is the ratio between…

Answer 9

the products and reactants in a reaction scheme

Question 10

Kc=

Answer 10

Kc= [C]^c [D]^d / [A]^a [B]^b

Question 11

Gas-phase Reactions:
Kp - used in reaction incl. only gas

Answer 11

Kp = PC^c PD^d / PA^a P B^b

Question 12

How set to up a Kp equation;

Answer 12

depends on how many moles of each molecule/compound

Question 13

Acid / Base Dissociation Constants:

Answer 13

Ka = [H+] [A-] / [HA]

Question 14

Thermodynamic Equilibrium constant (K) = Standard Equilibrium Constant KӨ

Answer 14

“Ratio of the thermodynamic activities of the products at equilibrium to those of reactants, considering stoichiometry”

Question 15

Define Thermodynamic Activity:

Answer 15

Effective measured concentration or pressure of a component at a given moment (equilibrium for K)

Question 16

What is unit of K

Answer 16

No units - its dimensionless

Question 17

When is K used?

Answer 17

Heterogeneous reactions – more than one phase
Instead of using KC or KP, K is used

Question 18

K must always be associated with a specified ________ and the equation of the reaction being considered

Answer 18

temprature

Question 19

The Reaction Quotient Q

Answer 19

Measure of the composition of the reaction mixture as the reaction progresses – not at equilibrium

Question 20

What do each letter of the equation mean?

Answer 20

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

Question 21

Q = pi (a(produts))^Vp / pi(a(reactants))^Vr

Question 22

Why use Q =

Answer 22

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

Question 23

Determine results of reaction:

Answer 23

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

Question 24

Equilibrium ______ when Gibbs energy is at its minimum (constant T and P).

Answer 24

reached

Question 25

The Equilibrium Constant (K) measures pressures (or concentrations)
Therefore, there is a quantitative relationship between ___ and _

Answer 25

∆G and K

Question 26

∆rG = -RT ln K

Answer 26

∆rG = standard Gibbs energy change
R = Gas constant (8.314jK^-1 mol ^-1)
T = temperature (K)
ln = natural logarithm
K = Thermodynamic equilibrium constant

Question 27

By rearranging this equation, the K value can also be calculated:

Answer 27

K = e(-∆Gr/RT)

Question 28

“ex” is the exponential function. e has a specific value =

Answer 28

2.718

Question 29

K gives information about the _______ of the reaction mixture at equilibrium

Answer 29

composition

Question 30

How K effects…

Answer 30

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

Question 31

When R <>P

Answer 31

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

Question 32

What is Le Chatelier’s Principle?

Answer 32

“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

Question 33

Effect of change in pressure:
N2O4 (g) <> 2NO2 (g)

Answer 33

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

Question 34

Changing number of components;
N2(g)+ 3H2 <> 2NH3 (g)
NH3 added to system will N2 and H2 increase of decrease?

Answer 34

Increase

Question 35

ICE table

Answer 35

initial
change
equilibrium

Question 36

Whta is importnat to remember in the ICE table?

Answer 36

RATIO of profucts and reactants

Question 37

If change in reactant goes down/up….

Answer 37

products will do the opposite (as they have to balance)

Question 38

ΔG = ΔH − TΔS

Answer 38

If ∆H and ∆S are independent of temperature, then ∆S/R is constant

Question 39

2 equations of ln K

Answer 39

ln K = contstant ΔH / R (1/T)
ln K = ∆rS/ R - ∆rH/ RT