Surface Chemistry Flashcards

Question

Define 'absorption'.

Answer 1

The process by which atoms, molecules or ions enter some bulk phase -> gas, liquid or solid material

Answer 2

- Simple adsorption involving the attractive forces between the molecules - Van der Waals’ forces. - Relatively weak non-specific interaction - Can form single or stacked layers - monolayers or multilayers - Equilibrium is reached rapidly

Answer 3

- Bond formation between the surface and the adsorbed species - Strong highly specific adsorption - Only monolayers can be formed - Equilibrium can be slower to attain

Answer 4

Extra (or excess) amount of surfactant at the surface

Answer 5

The molecular species that adheres to or is adsorbed in an extremely thin surface layer of another substance.

Answer 6

A condensed phase at which surface adsorption may occur

Answer 7

An expression describing the relationship between the amount of adsorbate adsorbed onto a surface at constant temperature and the equilibrium concentration of the substrate in contact with the adsorbent.

Answer 8

when the adsorbents are liquid and adsorbates are soluble in the adsorbent (e.g. surfactants in water)

Answer 9

- A solid surface contains a fixed number of adsorption sites - Each site can hold only one adsorbed molecule (monolayer) - The heat of adsorption is identical for all sites - There is no interaction between sites - The adsorbing solid behaves ideally

Answer 10

𝑥=𝑎𝑏𝑐/(1+𝑏𝑐) x is the amount of adsorbate adsorbed c is the concentration of the adsorbate at equilibrium (p for pressure also works) b is the Langmuir adsorption constant a is related to the surface area of the solid (often denoted as the maximum amount of adsorbate for the formation of a monolayer)

Answer 11

the ratio of the number of occupied sites to the number of available sites. Equivalent to x/a for the Langmuir Isotherm. 𝜃 can be from 0 to 1 where 1 represents all sites filled with adsorbate.

Answer 12

𝜃=𝑏𝑐/(1+𝑏𝑐)

Answer 13

𝑐/𝑥 = 1/𝑎𝑏 + 𝑐/𝑎 x = c y = c/x y intercept = 1/ab slope = 1/a

Answer 14

𝑝/𝑉 =1/𝑏𝑉𝑚 + 𝑝/𝑉𝑚 𝑝 the pressure of the adsorbate 𝑉 the volume of the adsorbent 𝑉𝑚 the volume corresponding to complete monolayer coverage A plot of p/V against p will give a straight line with an intercept of 1/(𝑏𝑉_𝑚 ) and a gradient of 1/𝑉_𝑚

Answer 15

Does not account for: - surface roughness - inhomogeneity - adsorbate/adsorbate interactions.

Answer 16

- An extension of the Langmuir isotherm to take account of multilayers forming through physisorption. - Often used to determine surface areas of solids in industry.

Answer 17

- Empirical - can't be derived from first principles. - Fits better than Langmuir for rough surfaces. - Encompasses surface heterogeneity and energy distribution for adsorption sites. 𝑥/𝑚=𝑎𝑐^(1∕𝑛) x is the amount of adsorbate adsorbed m is the mass of the adsorbent in grams c is the concentration of the adsorbate at equilibrium a and n are both Freundlich isotherm constants

Answer 18

𝜃=𝑎𝑐^(1∕𝑛)

Answer 19

Takin a logarithm of both sides. log⁡(𝑥/𝑚) = log⁡ 𝑎+ (1/𝑛) log⁡𝑐 A plot of log(x/m) against log c gives a straight line with an intercept of log a and slope of 1/n

Answer 20

-Takes into account adsorbate-adsorbate interactions. 𝜃 = 𝑘1 ln⁡(𝑘2𝑐)

Answer 21

𝑛_𝐽 (𝜎)=𝑛_𝐽 (total )−{𝑛_𝐽 (𝛼)+𝑛_𝐽 (𝛽)}

Answer 22

Γ𝐽=(𝑛𝐽 (𝜎))/𝜎 ``` 𝑛𝐽 = amount of J at interface. 𝜎 = surface area ```

Answer 23

The degree to which the surface tension is lowered by a substance is related to its surface excess d𝛾 = −∑Γ𝐽 d𝑛𝐽

Answer 24

d𝛾/(d ln⁡ 𝑐)= −Γ𝑅𝑇 ``` Γ = surface excess c = concentration of bulk solution 𝛾 = surface tension ```

Answer 25

𝜎 = 1/ (𝑁_A Γ) Γ is the surface excess concentration N_A is the Avogadro constant -> 6.023 x 1023 mol-1

Answer 26

A system where there is a dispersion of small particles of one material in another These small particles are often known as colloids Small means < 500 nm in diameter – too small to be seen with a standard microscope

Answer 27

- Light-scattering - Sedimentation - Osmosis

Answer 28

A homogenous mixture of two or more substances which is transparent with no light scattering from solute particles.

Answer 29

A mixture containing large, dispersed particles that can settle out or be separated by filtration. The aqueous layer is transparent with no light scattering.

Answer 30

A mixture containing particles small enough to remain suspended and not settle out. They are often opaque and exhibit significant light scattering.

Answer 31

a two-phase system in which one phase b (the dispersed phase) is dispersed into a second phase a (the continuous phase).

Answer 32

Solid Sol.

Answer 33

``` very large molecules commonly created by polymerization of smaller subunits. In biochemistry this includes: Nucleic acids Proteins Carbohydrates ```

Answer 34

The length of the macromolecule from tip to toe all along its length 𝑅_𝐶 = 𝑁𝑙 𝑁 is the number of monomer units of length 𝑙

Answer 35

𝑅_𝑟𝑚𝑠 = (2𝑁)^(1/2) 𝑙 𝑁 is the number of monomer units of length 𝑙

Answer 36

Measures the average distance between monomers and the center of mass. 𝑅_𝑔=(𝑁/3)^(1/2) 𝑙 𝑁 is the number of monomer units of length 𝑙

Surface Chemistry Flashcards

(65 cards)