topic six

Question 1

what requirements must be fulfilled for a chemical reaction to take palce

Answer 1

correct orientation
sufficent energy (reaching activation energy)

Question 2

what is activation energy

Answer 2

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

Question 3

what is the transition state

Answer 3

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 4

in general, faster reactions tend to haev lower or higher activation energies

Answer 4

lower, whereas slower reactions tend to have higher activation energies

Question 5

if activation enerfy is met will the reaction take place

Answer 5

if the correct orientation yes

Question 6

what is the maxwell boltzmann distribution

Answer 6

a graph where the x axis is kinetic energy and the y axis fraction of particles

Question 7

the area beneath the curve in the MB curve is directly proportional to

Answer 7

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

Question 8

as temp increases in the mb curve,

Answer 8

the particles gain ke and the curve flattens out

Question 9

how is the maxwell boltzmann distribution helpful

Answer 9

in understanding how changes in temperature and the use of a catalyst will affect the rate of a reaction.

Question 10

the rate of a chemical reaction is a measure of what of the reaction

Answer 10

the speed of the reaction

Question 11

what can the reate of reaction be defined as

Answer 11

the hange in conc of a reactant or product per unit of time

Question 12

rate of reaction =

Answer 12

change in reactant / change in time

increase in product conc / change in time

Question 13

rate of reaction is not constnat over the course of reaction so you must consider it at

Answer 13

a particular time

Question 14

how can instantaneous rate of reaction can be determined

Answer 14

graphically

Question 15

what is avg rate of reaction

Answer 15

calculated as the avergae over a particualr time period or interval

Question 16

what factors affect rate of reaction

Answer 16

temp (affects freq of collisions and energy they have)
concentration (affects freq of collisions)
pressure (affects freq of collisions)
surface area (increase as more molecules available)

Question 17

when does particle size affect rate of reaction

Answer 17

when the solid is being reacted directly, not when it is dissolved in solution.

Question 18

how do catalysts icnrease rate of reaction

Answer 18

providing an alternative reaction pathway so a greater proportion of reactant particles now have energy equal to, or greater than, the original activation energy for the reaction. This results in an increase in the frequency of successful collisions between reactant particles and an increase in the rate of reaction.

Question 19

catalysts at the end of a reaction

Answer 19

remains chemically unchanged and sometimes can be reused

Question 20

The factor by which the concentration of a reactant affects the rate of a reaction is known as

Answer 20

its order of reaction

Question 21

what is the only way the order of a reaction with respect to a particular reactance can be determined

Answer 21

through experimental data

Question 22

order of reactions can be:

Answer 22

zero, first or second order

Question 23

what does the rate expression give

Answer 23

the relationship between reactant concentrations and the rate of reaction.

Question 24

what is k

Answer 24

the rate constant

Question 25

what are the superscribts in hte rate expression

Answer 25

the orders of reaction with respect to the letter

Question 26

what is the overall order of reaction

Answer 26

the sum of indiviual orders of reaction

Question 27

zeroth order

Answer 27

Rate is independent of [A]; any change in the concentration of A does not affect the rate of reaction

Question 28

first order

Answer 28

Rate is directly proportional to [A]; if the concentration of A is doubled, the rate also doubles

Question 29

The rate constant k is a constant for

Answer 29

for a reaction at a particular temperature (it is temperature-dependent).

Question 29

second order

Answer 29

Rate changes as the square of [A]; if the concentration of A is tripled (3x), the rate increases by a factor of 9 (32 = 9)

Question 30

the rate expression gives the relationship between the conc of the reactants and the

Answer 30

overall rate of reaction

Question 31

k is only constant at

Answer 31

a particular temp it is temp dependent

Question 32

zero order units

Answer 32

mol dm-3 s-1

Question 33

first order units

Answer 33

s-1

Question 34

second order units

Answer 34

mol-1 dm3 s-1

Question 35

third order units

Answer 35

mol-2 dm6 s-1

Question 36

what type of graph can be used to find the order of a reaction with respect to a reactant

Answer 36

a concentration (y) time (x) graph or a rate (y) conc (x) graph

Question 37

for zero order, the ct graph is

Answer 37

straight line

Question 38

for first order ct graph, the line is

Answer 38

exponential curve

Question 39

for second order ct graph the line is a steeper

Answer 39

exponential curve

Question 40

for zero order rc graph

Answer 40

horizontal straight line

Question 41

for first order rc graph

Answer 41

straight line

Question 42

for second order rc graph

Answer 42

parabolic curve

Question 43

what is half life

Answer 43

the time it takes for the concentration of a reactant to decrease by half

Question 44

a reaction that takes place in a single step is known as a

Answer 44

elementary reaction

Question 45

Many reactions, however, do not take place in a single step and are called

Answer 45

non elementary reactions

Question 46

what are the steps in a non elementary reaction called

Answer 46

elementary steps

Question 47

the slowest elementary step in a reaction mechanism is the

Answer 47

rds

Question 48

the elementary steps must add together to give

Answer 48

the overall balanced equation for the reaction

Question 49

the rate expression deduced from the rate-determining step must be consistent with

Answer 49

the experimentally determined rate expression

Question 50

The NO3, which appears in both steps but not in the overall equation, is known as

Answer 50

a reaction intermediate.

Question 51

what does moelcularity tell us

Answer 51

the number of reactant particles in an elementary step

Question 52

If only one particle is involved in the elementary step, it is

Answer 52

unimolecular

Question 53

If two reactant particles are involved,

Answer 53

it is bimolecular

Question 54

if three reactant particles are involved,

Answer 54

termolecular

Question 55

if two reactant particles are involved

Answer 55

its bimolecular

Question 56

if three reactant particels are involved

Answer 56

termolecular

Question 57

what is an intermediate

Answer 57

a species that is formed from the reactants in a chemical reaction which then goes on to react further to form the products.

Question 58

what is the transition state

Answer 58

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 59

the rds has the highest

Answer 59

activation energy as its the slowest

Question 60

why do catalysts appear in the elementary steps of a reaction mechanism and in the rate-determining step but not in the overall balanced equation for the reaction

Answer 60

they are chemically unchanged and can be reused

Question 61

what value constant does a catalyst change

Answer 61

increasing the value of the rate constant k

Question 62

what maeks somehting bimolecuelar

Answer 62

elementary steps have two reactant particels

Question 63

rate constant k is temp dependent, this relatiponsh[ is shown by the arrhenius equation:

Answer 63

k=Ae ^−Ea/RT

Question 64

what is a in the arrhenius equation

Answer 64

the pre-exponential factor or the frequency factor.

Question 65

what is Ea in the arrhenius equation

Answer 65

activation energy (J/mol^-1)

Question 66

what is r in the arrhenius equation

Answer 66

universal gas constant (8.31 J K^1mol^-1)

Question 67

what is e in the arrhenius equation

Answer 67

eulers number

Question 68

what does the arrhenius constant take into account with a

Answer 68

the frequency of collisions and the probability that they have the correct orientation (or geometry)

Question 69

The expression (e−Ea /RT) (the exponential factor) is the fraction of molecules that have

Answer 69

sufficient kinetic energy to react at a certain temperature

Question 70

modified version of arrhenus equation (to find ativation energy)

Answer 70

lnk=−Ea/RT +lnA

Question 71

lnk =−Ea/RT +lnA is a form of y = mx+c

Answer 71

therefore, a graph of ln k against 1/T gives a straight line (Figure 1). The gradient of the line is equal to –Ea/R (where R is the universal gas constant with a value of 8.31 J K−1 mol−1). The intercept on the y-axis is equal to ln A. Once we have determined the activation energy for the reaction, we can calculate the Arrhenius constant by substituting the activation energy value into the Arrhenius equation.

Question 72

Gradient=

Answer 72

−Ea/R

Question 73

−Ea=

Answer 73

gradient×R

Question 74

the rate constant, k, for a reaction increases ???? with increasing temperature

Answer 74

exponentially