6 chemical kinetics

Question 1

define chemical kinetics

Answer 1

the study of factors affecting the rate of a chemical reaction.

Question 2

what is the rate of a chemical reaction

Answer 2

the increase in concentration of one of the products per unit time or as the decrease in the concnetration of one of the reactants per unit time

Question 3

what is rate of reaction measured in

Answer 3

mol dm^-3 s^-1

Question 4

how can you measure change in conc

Answer 4

using any property that differs between the reactants and products.
mass or volume changes
absorption using a spectrometer when there is colour change
pH changes when there is a change in acidity
electrical conductivity when there is a change in ionic concentrations.

Question 5

what do you do with data (from a data logger) about a a change in conc

Answer 5

a graph is plotted (concentration against time)
rate at any stated point in time is then the gradient of the graph at that time. rates of reaction usually decrease with time as the reactants are used up

Question 6

what is a maxwell boltzmann curve

Answer 6

the distribution of kinetic energies.

number of particles (y) vs kinetic energy (x)

Question 7

would a high temperature have a high y value or low on the maxwell boltzmann curve

Answer 7

lower, as the curve would broaden, as the increase of kinetic energy is counted on the x axis.

Question 8

how to find rate of reaction from a graph

Answer 8

change in time (x)

Question 9

when a rate of reaction graph line goes flat what does it mean

Answer 9

the reaction has gone to completion

Question 10

for particles to have a reaction, what 3 requirements need ot be met

Answer 10

particles must collide
they must collide in the correct orientation.
must collide with sufficent energy to bring about the reaction.

Question 11

what is the minimum amount ofenergy required for a reaction to occur called

Answer 11

activation energy

Question 12

factors affecting rate of reaction

Answer 12

temperature
surface area
concentration
catalyst

Question 13

how does temperature increase rate of reaction

Answer 13

particles move faster
more collisions per second
particles will have gained KE, and consequently more will reach activation energy.

Question 14

an increase of about 10 degrees celsius

Answer 14

doubles rate of reaction

ROUGHLY

Question 15

how does surface area increase rate of reaction

Answer 15

in a solid, only particles on the surface can come into contract with a surrounding reactant, so increasing the surface area allows more to be in contact, increasing number of collisions.

Question 16

how does concentration increase rate of reaction

Answer 16

more collisions per second per unit volume, as there are physically more particles to collide.
as reactants get used up, their concentration decreases.

Question 17

how do catalysts work

Answer 17

increase rate of reaction without themselves being chemically changed.
they bring down the activation energy by bringing the reactive parts of the reactant particles into close contact. this provides an alternative pathway for the reaction with lower activation energy.

Question 18

how can you find rate of reaction from a graph

Answer 18

find the gradient by change in y over change in x

Question 19

maxwell boltzmann distribution graph axis’

Answer 19

y: number of particles
x: kinetic energy

Question 20

describe increasing temperature and its effect on a maxwell boltzmann graph

Answer 20

the area under the curve does not change as the total number of particles remains constant. more particles have a high velocity, so the curve broadens to the right of the original peak

Question 21

describe decreasing temperature and its effect on a maxwell boltzmann graph

Answer 21

the area under the curve does not change as the total number of particles remains constant. peaks higher and before the original peak.

Question 22

describe adding a catalyst and its effect on a maxwell boltzmann graph

Answer 22

no change. mark the lower activation energy on the graph though.

Question 23

describe changing volume and its effect on a maxwell boltzmann graph

Answer 23

no change

Question 24

describe adding an inert gas and its effect on a maxwell boltzmann graph

Answer 24

no change

Question 25

when will a collision be unsuccessful

Answer 25

when they do not reach activation energy

incorrect orientation

Question 26

Ea means

Answer 26

activation enerfy

Question 27

what is activation energy

Answer 27

the minimum amount of energy that colliding particles must have for a chemical reaction to occur.

Question 28

activation energy is the difference in energy between the..

Answer 28

reactants and the transition state of the reaction (peak of profile)

Question 29

what is the transition state

Answer 29

the highest energy state on a reaction coordinate; it indicates a point at which new bonds are being formed at the same time as old bonds are being broken.

Question 30

key feature of the maxwell boltzmann distribution

Answer 30

the total area beneath the curve is equal to the total number of particles in the sample

Question 31

the area under any region of a maxwell boltzmann curve is directly proportional to

Answer 31

the number of molecules having a value of kinetic energy in that range.

Question 32

when is the curve highest

Answer 32

at the most probable value of kinetic energy

Question 33

rate of reaction =

Answer 33

decrease or increae in concentration
/
changein time

Question 34

Rate=

Answer 34

Δ[Product] / ΔT

Question 35

unit for rate of reaction

Answer 35

mol dm–3 s–1.

Question 36

how can instantaneous rate of reaction can be determined graphically

Answer 36

from a change in reactant or product divided by time

Question 37

how can avergae rate of reaction be dtermined graphically

Answer 37

from a change in reactant or product divided by time but over a particualr time period or interval

Question 38

what is the instantaneous rate of reaction

Answer 38

the rate of reaction at any particular point in time.

Question 39

instantaneous rate of reaction is equal to

Answer 39

gradient of the line at that point

Question 40

the steeper the gradient,

Answer 40

the faster the rate of reaction

Question 41

catalyst in the haber process

Answer 41

powdered iron

Question 42

catalyst in the contact process

Answer 42

platinum

Question 43

what do catalysts do

Answer 43

providing an alternative reaction pathway that has a lower activation energy

Question 44

what remains unchanged with the addition of a catlayst

Answer 44

original activation energy and products formed