catalysts

Question 1

what is a catalyst

Answer 1

speed up the rate of reaction providing an alternative pathway with a lower activation energy without getting used up itself

Question 2

why do transition metal form good catalyst

Answer 2

as they form variable oxidation states

Question 3

what is a heterogenous catalyst

Answer 3

where the reactants and catalyst are in a different physical state

Question 4

what is a homogenous catalyst

Answer 4

when the catalyst and the reactant are in the same physical state

Question 5

what is autocatalyst

Answer 5

the catalyst is a product of the reaction which is the same state as the reactant product

Question 6

what is the structure of a catalyst and why

Answer 6

it is a honeycomb structure which provides a large surface area and minimises cost of energy ,

Question 7

how is it made

Answer 7

a thin layer of expensive metal is placed on the structure so molecule can recat at a given time

Question 8

how does reaction occur in general

Answer 8

adsorption then reaction the desorption

Question 9

where does the reaction take place

Answer 9

at the surface of the catalyst

Question 10

what happens frst

Answer 10

reactants are adsorped to the binding sites on the surface of the catalyst and form weak chemical bonds with the active site

Question 11

what happened next

Answer 11

bonds in reactants are weakened and react to form other bonds

Question 12

what happened in the last stage

Answer 12

the products are desroped

Question 13

what are the benefits of adsorption

Answer 13

weakens the bonds within the reactants so lower activation energy required to break bonds
increase surface concentration of reactant molecules so increase collision frequency
provides reactant with correct orientation for reaction to occur

Question 14

what does the strength of adsorption determine

Answer 14

the effect of the catylitic ability

Question 15

what if it is too weak

Answer 15

silver is too weak and the reactants are too mobile

Question 16

what if adsorption is too strong

Answer 16

tungsten which means the reactant and products cannot leave active site once formed

Question 17

how do catalyst get poisoned

Answer 17

the impurities are strongly adsoped on the surface of the catalyst reduces the surface area for the catalyst and slows down rate of reaction

Question 18

why is it more expensive

Answer 18

decreases the amount of product formed in a certain time or with a certain amount of energy eventually need to be replaced

Question 19

why was lead poisonous

Answer 19

it was included in petrol and used to bind to active site and decrease the surface area for reaction to occur

Question 20

why is sulphur poisonous

Answer 20

it poisons the iron in the haber process and reduces the surface are afor reaction to take place n

Question 21

how do catalyst work in homogenous system

Answer 21

as the two ions are negatively charged, so they repel each other so unlikely to collide the catalyst is a poisitve ion so can attract and activation energy lowered

Question 22

give an example of a homogenous catalyst

Answer 22

s208 and iodine with iron

Question 23

what happens to the rate of reaction in an autocatalyst recation

Answer 23

at the start of reaction the rate of reaction is slow as both reactants repel each other so activation energy is high, as the catalyst is formed so can attract the reactants and the activation enrgy is lowered and reaction increases