Rate Equations

Question 1

Rate of reaction

Answer 1

The change is concentration of a substance in a given time

Question 2

Units of rate

Answer 2

Moldm-3s-1

Question 3

Reactions can only occur when…

Answer 3

Collisions take place between particles having sufficient energy

Question 4

What is the sufficient energy called

Answer 4

Activation energy

Question 5

Activation energy

Answer 5

The minimum energy required to start a reaction by the breaking of bonds

Question 6

How does increasing conc increase rate of reaction

Answer 6

• more particles in given volume

- more frequent successful collisions

Question 7

How does increasing pressure increase rate

Answer 7

• increasing pressure means same particles in a smaller volume
• more frequent successful collisions

Question 8

How does increasing SA of a solid increase rate

Answer 8

Powders increase SA- more frequent successful collisions

Question 9

How does increasing temp increase rate

Answer 9

(Maxwell Boltzmann) more particles with energy equal to or greater than Ea so more successful collisions

Question 10

How does a catalyst increase rate

Answer 10

Provides alternative pathway with lower Ea so far more molecules have Energy equal to or greater than activation energy

Question 11

what does the rate equation show

Answer 11

the relationship between the rate of a reaction and the initial conc of the reactants

Question 12

general rate equation

Answer 12

rate= k[A]m [B]n

Question 13

what is [A] in rate equation

Answer 13

conc of A

Question 14

what is [B] in rate equation

Answer 14

conc of B

Question 15

what is m in rate equation

Answer 15

order with respect to A

Question 16

what is n in rate equation

Answer 16

order with respect to B

Question 17

what is k in rate equation

Answer 17

rate constant

Question 18

what is the overall order of a reaction

Answer 18

the sum of the individual orders

Question 19

half life

Answer 19

the time taken for the concentration of a reactant to half

Question 20

how would zero order be shown on a conc-time graph

Answer 20

straight line indicating uniform day

Question 21

how would first order be shown on a conc time graph

Answer 21

curve- equal half lives

Question 22

how would second order be shown on a conc time graph

Answer 22

steeper curve- half lives increase

Question 23

what is the gradient at a particular time on a conc time graph a measure of

Answer 23

the rate at that time

Question 24

how to determine order of ror with a conc time graph

Answer 24

• start with known conc of a and b
• ensure conc of one (b) is much larger than other- remains constant
• determine conc of A at different times
• plot graph
• continuous monitoring method

Question 25

how can rate-conc graph be plotted

Answer 25

- conc-time graph plotted - tangents drawn, giving ror values - rate-conc graph plotted

Question 26

rate graph zero order

Answer 26

flat line

Question 27

rate graph first order

Answer 27

straight diagonal line, positive gradient

Question 28

rate graph second order

Answer 28

curve

Question 29

what is k

Answer 29

a proportionality constant that links rate of reaction with the concentrations of reactants

Question 30

correlation between value of k and rate

Answer 30

k larger- faster rate

Question 31

what do the units of k depend on

Answer 31

overall order of reaction

Question 32

what do chemical reactions often take place in

Answer 32

a series of steps called the reaction mechanism

Question 33

what can the rate equation provide clues about

Answer 33

a likely reaction mechanism by identifying slowest stage of a reaction sequence

Question 34

rate determining step

Answer 34

slowest step in a reaction mechanism

Question 35

what will any step that occurs after rate determining step not affect

Answer 35

overall rate- reactants involved in later steps wont appear in rate equation

Question 36

how can you tell if the reaction is a one step process

Answer 36

the powers in the rate equation match the stoicheometry of the overall equation

Question 37

how can you tell if the reaction has more than one step

Answer 37

the powers of the rate equation don't match the overall equation

Question 38

what always increases when temperature is increased

Answer 38

the rate of reaction- Maxwell districution

Question 39

if the temperature is increased in a reaction, why must k increase as rate increases

Answer 39

if [A] and [B] are kept constant k must increase | rate=k[A]m[B]n

Question 40

what is the increase of k with temperature

Answer 40

exponential

Question 41

what is the relationship between rate constant and temp described by and what does it allow us to work out

Answer 41

Arrhenius equation | allows us to work out Ea

Question 42

the Arrhenius equation

Answer 42

k=Ae^-Ea/RT

Question 43

what does k mean in Arrhenius equation

Answer 43

rate constant

Question 44

what does A mean in Arrhenius equation

Answer 44

Arrhenius constant

Question 45

what does ea mean in Arrhenius equation and units

Answer 45

activation energy (J)

Question 46

what does R mean in Arrhenius equation

Answer 46

ideal gas constant

Question 47

what does t mean in Arrhenius equation and units

Answer 47

temperature (K)

Question 48

how can the Arrhenius equation be rearranged

Answer 48

by taking the natural log (ln) of both sides

Question 49

Arrhenius equation rearranged

Answer 49

lnK=lnA -Ea/RT

Question 50

what form can rearranged Arrhenius equation rearranged be expressed in

Answer 50

y=mx+c

Question 51

how can Arrhenius equation be used to determine the activation energy of a reaction

Answer 51

- k can be determined at different temperatures - graph poltted with k on y axis and 1/T on x axis - line of best fit is a straight line and so can be described as y=mx+c