kinetics

Question 1

what is rate of reaction

Answer 1

the change of concentration of reactant or product per unit time

Question 2

what is rate

Answer 2

amount of reactant used/product made
over time

Question 3

what is collision theory

Answer 3

for a reaction to occur the particles must collide in the right direction and they must also have a minimum amount of kinetic energy (the Ea)

Question 4

what is activation energy

Answer 4

the minimum amount of energy required for a reaction to occur

Question 5

what is the peak on a maxwell boltzmann distribution graph

Answer 5

the most likely energy of a particle in a sample

Question 6

where is the mean energy on maxwell boltzmann distribution graph

Answer 6

right from the most likely energy

Question 7

factors of maxwell boltzmann distribution graph

Answer 7

starts at 0,0 as no particles have no kinetic energy
area under curve is equal to total number of molecules
y axis = number of molecules
x axis = kinetic energy

Question 8

how does temperature affect rate of reaction

Answer 8

particles have on average more kinetic energy when heated

larger proportion of particles will have energy greater than the activation energy

Question 9

temperature on maxwell boltzmann distribution

Answer 9

curve shifts to the right
peak is lower
area under curve is the same
area under curve beyond Ea increases
Ea stays the same

Question 10

why do we get a faster rate of reaction when temperature is increased

Answer 10

particles move around more at higher temperatures
there are more frequent successful collisions which are more energetic

Question 11

why do we get a faster rate of reaction when pressure or concentration is increased

Answer 11

particles are closer together so collide more often
there are more frequent successful collisions and so higher chance of a reaction

Question 12

what is a catalyst

Answer 12

a substance than increases the rate of reaction by providing an alternative pathway that has a lower activation energy, it remains chemically unchanged

Question 13

how do catalysts affect industry

Answer 13

1) lowers temperature needed = less money spent on energy and less co2 produced
2) speed up reaction so faster production
3) change properties of a product
4) less waste produced as catalysts allow reactions with better atom economies

Question 14

what is a heterogeneous catalyst

Answer 14

in a different phase (state) from the reactants

Question 15

what happens when surface area is increased with heterogeneous catalyst

Answer 15

increase rate of reaction as more particles can react with catalyst at the same time

Question 16

what is a homogeneous catalyst

Answer 16

in the same phase (state) as the reactants

Question 17

how do homogeneous catalysts work

Answer 17

they form an intermediate by reactants combining with catalyst to form a product. catalyst is reformed again

Question 18

how do heterogeneous catalysts work

Answer 18

1) substances adsorb to the surface of catalysts
2) bonds in reactants weaken and break to form radicals and radicals react together to form new substances
3) new molecules desorb from surface of catalyst

Question 19

how do homogenous catalysts affect energy profile diagrams

Answer 19

they have 2 activation energies (double bump, 1st is higher)
1st - forms intermediate
2nd - intermediate breaks

Question 20

what is the affect of increased surface area on the rate of reaction

Answer 20

more frequent successful collisions as more surface for particles to collide with

Question 21

catalyst on Maxwell Boltzmann distribution graph

Answer 21

area under curve is the same
peak is same
Ea shifts left
more particles with Ea

Question 22

what is order of a reaction

Answer 22

the power to which the concentration of that reactant is raised in the rate equation

Question 23

when is the rate constant constant

Answer 23

when the temperature is constant

Question 24

what is rate equation

Answer 24

rate = K [A]a [B]b

Question 25

zero order reaction

Answer 25

no impact on rate rate-conc graph straight line rate=K

Question 26

first order reaction

Answer 26

conc and rate directly proportional rate=K[A]

Question 27

second order reaction

Answer 27

rate proportional to conc squared rate=K[A]^2

Question 28

conc time graph zero order

Answer 28

linear

Question 29

conc time graph first and second order

Answer 29

both curved second order has kink

Question 30

define half life

Answer 30

time taken for initial conc of the reactants to decrease by half

Question 31

what is the half life in first order reaction

Answer 31

stays constant at 100 50 and 25%

Question 32

what are experimental techniques used to obtain rate data

Answer 32

measuring change in reactant/ product mass/conc over time - produces gas change in electrical conductivity - loss/gain of ions change in pH

Question 33

how can you find rate of reaction from mass change

Answer 33

if gas is produced then mass decreases as reaction proceeds plot mass-time graph

Question 34

how can you find rate from volume of gas evolved

Answer 34

measure volume of gas produced over time in reaction plot volume-time graph

Question 35

how to use titration to work out rate of reaction

Answer 35

small samples of a reaction mixture can be removed at regular intervals throughout a reaction and titrated to find a concentration of a reactant/product

Question 36

how to use colorimetry to work out rate of reaction

Answer 36

for a reaction that involves the formation of a coloured species colorimeter used to measure absorbance of light of solutions at known concentrations then the absorbance of samples from reaction mixture can be measured to convert calibration curve to conc readings

Question 37

what is the rate determining step

Answer 37

the slowest step in a multi step chemical reaction

Question 38

what is the Arrhenius equation

Answer 38

k=Ae^ -Ea/RT OR lnK = lnA -Ea/RT

Question 39

describe Sn1 reaction mechanism

Answer 39

the leaving group leaves first forms a carbocation intermediate 1st step is rate determining so rate equation is conc of haloalkane

Question 40

describe Sn2 reaction mechanism

Answer 40

leaving group leaves while the nucleophile attacks the molecule rate equation is conc of haloalkane and nucleophile

Question 41

how to slow down titration to get rate values

Answer 41

-cool it down -add distilled water -add chemical to stop reaction (quenching) if we didn't slow down reaction the conc would proceed to change as you conduct titration

Question 42

what is a colorimeter

Answer 42

measures absorbance of light in a coloured sample, if it is more concentrated the colour is darker hence more light is absorbed

Question 43

propanone plus iodine colour change

Answer 43

brown to colourless

Question 44

in what conditions will k change in the rate equation

Answer 44

if temp increases then k increases

Question 45

why does temperature increase k in rate equation

Answer 45

more kinetic energy-> more collisions -> higher rate concs stay constant so k must increase

Question 46

what assumptions do you make in clock reaction

Answer 46

RATE IS CONSTANT until event occurs conc of reactants doesn't change significantly temp remains constant reaction has not proceeded too far when the end point is seen

Question 47

why does half life not change in zero order

Answer 47

rate is constant as conc doesn't affect rate so half life will decrease

Question 48

why is there another substance in rate equation that isn't a reactant

Answer 48

it is a catalyst

Question 49

why do tertiary haloalkanes proceed by sn1

Answer 49

less space around carbon being attacked as it is bonded to multiple other carbons so it is more stable

Question 50

what happens to rate constant when activation energy gets smaller

Answer 50

gets bigger as the activation energy drops the rate of reaction increases as more particles have enough energy to collide