Rates - PowerPoint Presentation

Slide1

Rates of Reactions – Part 2Slide2

Factors affecting the rate

of reaction

The

surface

area

The

concentration

of

the

reactant

The

temperature

at

which

the

reaction

is

carried

out

The

use

of

a

catalyst

The

influence

of

lightSlide3

4. Rate of Reaction – Effect

of Catalyst

Hydrogen

peroxide

water

+ oxygen

Powdered

manganese

IV

oxide

MnO

2

is

added

as

a

catalyst

.

The

more

finely

ground

up

the

manganese

oxide

is

the

faster

the

reaction

goes

.

The

mass

of

the

manganese

oxide

remains

the

same.

It

is

a

catalyst

.Slide4

Effect of Catalyst

The

more

catalyst

you

use the faster

the reaction

.

The type

of

catalyst

you

use

will

effect

the

reaction

.Slide5

Definition of a Catalyst

A

catalyst

is

a

substance that increases the rate of

a chemical reaction. The catalyst

remains chemically

unchanged

.Slide6

How does a catayst work

?

The

provide

a

surface

on which other molecules or atoms

can react.Slide7

Catalysts in Industry

Catalysts are

very

useful

as you only need a small amount

to dramatically change

the rate of a reaction

.

The

catalyst

is

not

used

up

so

can

be

used

again

and

again

.

Used

in

the

production

of

polythene

,

painkillers

,

fertilizers

and

fabrics

.

The

processes

to

make

these

compounds

,

without

catalysts

,

would

need

much

more

energy

and

be

much

more

costly

.Slide8

Catalytic Convertors

Used on

cars

to

reduce pollution.Car exhausts produce CO, NO and unburnt

hydrocarbons.The catalytic convertor

converts these

to

less

harmful

products

CO

2

, N

2

and

water.The catalytic convertor removes polluting oxides and completes the oxidation of unburnt hydrocarbons.Slide9

Catalytic Converters

Rhodium

and

platinum

–

precious metals usedSlide10

Biological Catalysts

Living cells also

produce

catalysts

,

these are protein molecules called enyzmes.

Characteristics;Enzymes are proteins

Very specific –

control

only

one

reaction

Temperature

sensitive –

stop

working

above

45oCpH sensitive – work best at pH 7Slide11

Enzymes in Industry

Biological washing

powders

use

enzymes to remove biological stains (

sweat, blood, food).The

enzymes break down protiens and

fats

.

Because

the

enzymes

are

temperature

dependent

they need a wash of no more than 40oCSlide12

Surface Catalysts and

Collision Theory

One

main

type

of catalyst works by absorbing

the reactant molecules onto

a solid surface. This

process

of

adsorption

brings

the

reacting

molecules

closer together.Slide13

Nickel Catalyzed Hydrogenation

Finely divided

nickel

is

used as a catalyst to add hydrogen to

unsaturated hydrocarbons.Slide14

Collision Theory

If a reaction

only

occurs

when particles collide with the surface

of a solid….Then it

follows that the

more

surface

area

you

have

,

the

more

collisions you have, the faster the reaction is.This also applies if; solutions are

more

concentrated

Gases

are

more

compressed

Increasing

the

temperature

increases

the

speed

the

particles

are

moving

again

increasing

the

probability

of

collision

.Slide15

Activation Energy

Not

every

collision

produces a reaction.A certain amount of energy

needs to be present

to break the

bonds

, E

A

A

catalyst

increases

the

rate

of

reaction

by reducing the EASlide16

Activity Page 216

Exercise 7.4 on worksheet

Read

about

photochemical

reactions and do questions on page 218