Phys Need To Know

Question 1

TF

the Langmuir isotherm assumes that adsorption is non dissociative

Answer 1

True

Question 2

TF
THE Langmuir isotherm assumes coverage stops after one mono layer

Answer 2

True

Question 3

TF
the Langmuir isotherm assumes absorption sites can be different

Answer 3

False
They are all identical in this assumption

Question 4

TF
the langmiur isotherm assumes there is no interaction between sites

Answer 4

True

Question 5

In the Langmuir isotherm, what relationship do pressure and adsorption have ?

Answer 5

Absorbance increases as pressure increases until a point B where absorbance plateaus as we have reached full mono layer coverage

Question 6

For a single atom molecule rate of adsorption is …

Answer 6

Rads = ka Ns (1-theta) S

Question 7

If an isotherm has a hysteresis loop it indicates what

Answer 7

Pores filling them emptying (mesoporous material)

Question 8

If an isotherm takes a shape where it increases plateaus and then increases again what is this indicative of?

Answer 8

Multilayer adsorption, it plateaus after one mono layer coverage and then increases as a multilayer is formed

Question 9

At EQBM surface coverage in terms of rate =

Answer 9

Theta = Kp/ (1+Kp)

Question 10

For isotherms that don’t take Langmuir shape we use the …… isotherm instead

Answer 10

Braunder emmett teller (BET) isotherm

Question 11

In a rate eqn (surface coverage) :
What are powers to the half indicative of ?

Answer 11

Dissociative chemisorption

They come from the individual rate equations for dissociative chemisorption where they are squared as we need 2 vacant sites adjacent for this to occur.

Question 12

In a rate eqn :
Squared implies …

Answer 12

Competitive adsorption in a langmiur hi shell wood mechanism

Question 13

Signifies what type of adsorption?

Answer 13

Dissociative chemisorption

Question 14

What can we tell about the adsorption from this eqn ?

Answer 14

Competing species for the same site

We have an extra denominator for the competing species

Question 15

What type of mechanism does this rate eqn demonstrate?

Answer 15

ELAY RIDEAL
No k terms for B2 as there is no eqbm established between B2 gas and B2 ads on the surface

Mechanism in which A ads and it reacts with Bgas that’s not adsorbed to give a products in gas phase.

Question 16

What happens in the elay rideal mechanism

Answer 16

A ads reacts with B2 gas to produce product (gas)

Question 17

RDS of elay rideal mechanism

Answer 17

The reaction
A ads + B2gas - - - - products (gas)

Question 18

Langmiur hinshelwwod mechanism RDS?

Answer 18

The reaction fully in the adsorbed layer
Aads + B ads ==== products ads

(Reversible)

Question 19

What happens in the langmiur hinshelwood mechanism

Answer 19

A and B are both adsorbed and they react whilst adsorbed to create an adsorbed product that is then described

Question 20

If there is a product term in the rate eqn for a catalytic process, which mechanism has it gone by?

Answer 20

Langmiur hinshelwood because the product is formed in the adsorbed layer so can compete with a and b

Question 21

What imechansim is this process indicative of?

Answer 21

Langmiur hinshelwwod

Question 22

If B is a poison is present how does it effect the eqn for surface coverage A (theta A)?

Answer 22

Theta A = kapa/ 1 +kapa +kbpb as b and a are competing

If b is a poison ! Kb» ka so kbpb term dominates

Therefore thetaA = kapa/ kbpb

Surface coverage of A is LIMITED BY POISON B

Question 23

TF

in a volcano plot, the RDS is different at either side

Answer 23

True

Question 24

TF
promoters are electronegative elements

Answer 24

FLASE
they are electro positive elements

Question 25

TF promotors have low surface energies compared to catalyst

Answer 25

True They will segregate to the surface so stabilise the surface and keep the particles small Increase surface area

Question 26

TF Promotors can increase surface area of catalyst

Answer 26

True

Question 27

TF Binding strength of adsorbed molecules is dependent on energy of fermi level EF

Answer 27

True

Question 28

TF For a single atom on m catalyst, across a period binding strength between an adsorbed molecule and a catalyst increases

Answer 28

False Binding strength decreases across a period as delta h decreases

Question 29

WHat type of bonding is dominant between catalyst surface and adsorbent species

Answer 29

Covalent

Question 30

TF BINDING STRENGTH OF ABSORBED SOECIES AND CATALYST IS DEPENDENT ON BAND OCCUPATION

Answer 30

True - this is dependent on fermi level which effects binding strength

Question 31

TF FOR DIATOMIC ATOMS ON M CATALYST, EG H2 ELECTRON DENSITY IN SIGMA * OF H-H BOND MAKES IT MORE LIEKLY TO DISSOCIATE

Answer 31

True

Question 32

What effect will this have on M-H bond and H-H bond

Answer 32

m-h weakened because there is energy in anti bonding bands (sigma) H-h weakened because there is E density on the sigma * bands which will weaken the h-h bond

Question 33

TF FOR diatomic molecules the position of Ef determines if dissociative adsorption occurs

Answer 33

True

Question 34

For CO What effect would scenarios 1 and 2 have on M-C and C-O bonds

Answer 34

1) increase M-C strength because bonding band for the sigma donation of c onto m (lowest band) Increase m-c strength because bonding band of backdonation from m-c is filled (higher bonding band) C=O strength . Whilst b2 is a bonding band, it arises from the interaction of an anti bonding orbital on c=o so will actually weaken c=o bonds. 2) anti binding band decreases m-c strength so it may react more readily as it is not held so tight to the catalyst Binding band 2 has same effect at weakening CO as above

Question 35

TF binding strength and reactivity of adsorbates on a catalytic surface are independent of fermi level

Answer 35

FALSE, they are highly influence pd by fermi level

Question 36

TF Activity / catalytic performance depends on surface type

Answer 36

True (but not much)

Question 37

TF Activity / catalytic performance depends on dektaHads

Answer 37

True

Question 38

Relationship between activity and strength of chemisorption

Answer 38

Activity (alpha) = 1/ strength of chemisorption

Question 39

Lifetime of absorbance on a surface (Tao)

Answer 39

Tao = 1/v V = vibrational frequency

Question 40

How far does a molecule travel on a surface before diffusing?

Answer 40

Question 41

TF Catalytic performance depends on deltaH ads

Answer 41

TRUE DEPENDS CRITICALLY ON IT refer to volcano plots

Question 42

TF catalytic supports maximise sintering effects

Answer 42

False they minimise sintering effects (agglomeration)

Question 43

TF Catalyst supports allow high diesperion of small particles

Answer 43

True Small particles on surface to maximise surface area

Question 44

TF bulk solids are always preferred as supports

Answer 44

False When unsupported metal catalysts are sufficiently active, porous sponges or gauze or wire like materials are preferred over bulk solids as supports.