module 3+5: rates of reaction

Question 1

what is the order in respect to the reactant when:
reactant concentration doubles and rate stays the same

Answer 1

order 0

Question 2

what is the order in respect to the reactant when:
reactant concentration doubles and rate doubles

Answer 2

order 1

Question 3

what is the order in respect to the reactant when:
reactant concentration doubles and rate quadruples

Answer 3

order 2

Question 4

how do you calculate the overall order

Answer 4

find the sum of the reactant’s orders

Question 5

what equation is used with orders and the rate constant

Answer 5

.

Question 6

how do you find the units for K

Answer 6

rate is: mol/dm³/s

sub into an eq. and cancel out values to find thge units of k

Question 7

what does this concentration-time graph show?

Answer 7

0 order

Question 8

what does this concentration-time graph show?

Answer 8

1 order

Question 9

how can you calculate the order of a reaction using half lives

Answer 9

zero order: successive half lives decrease with time
first order: half life remains constant
second order: successive half lives increase with time

Question 10

what order does this rate-concentration graph show

Answer 10

order 0

Question 11

what order does this rate-concentration graph show

Answer 11

first order

Question 12

what order does this rate-concentration graph show

Answer 12

second order

Question 13

what is the rate-determining step

Answer 13

the step that determines the rate of the reaction, the slowest step

all reactants from the rate equation will appear in the rate-determining step

Question 14

what is the d-block

Answer 14

elements whose highest occupied energy level is a d sub-shell

Question 15

what are the elements of the arrhenius equation and units

Answer 15

.

Question 16

how does pressure influence rate of reaction

Answer 16

higher pressures compress gases into a smaller volume, thus increasing concentration so that collisions are at a higher frequency because there are more particles per unit area

Question 16

how does surface area impact rate of reaction

Answer 16

grinding a solid increases the SA/V ratio, so the frequency of collisions increases as there are more surfaces for collisions to occur

Question 17

how do catalysts affect reaction rate

Answer 17

they increase it without being used up
they may react to form an intermediate but are then regenerated they lower activation energy through providing an alternate reaction pathway

Question 18

describe the Boltzmann distribution curve and how it changes with temperature and catalysts

Answer 18

line starts at 0 bc no molecules have 0 energy
line never again meets the x axis bc there’s no max energy
the area under the curve = total no. of particles

Question 19

define homogeneous catalysts

Answer 19

the catalysts and reactants are in the same physical state, usually both aqueous

Question 20

define heterogeneous catalysts

Answer 20

the catalyst and reactants are different physical states, usually where reactants are gases but the catalyst is a solid

Question 21

what are economic and sustainability advantages of catalysts

Answer 21

• using a catalyst can mean lower temps and pressures can be used, saving energy costs
• saving energy costs means less us of fossil fuels/electricity which means less CO2 emissions
• catalysts can enable reactions to be used which have better atom economies

Question 22

what is a half life

Answer 22

how long it takes for half of a reactant to be used up

Question 23

why is it unlikely for some reactions to take place in one step

Answer 23

1. a collision is unlikely between more than 2 species
2. the stoichiometry in the rate equation doesn’t match the overall equation

Question 24

define rate of reaction

Answer 24

the change in amount of reactant or product per unit time

Question 25

what does the line on a conentration-time graph represent

Answer 25

rate

Question 26

what parts of the equation do you use when writing a Kp equation

Answer 26

GASES ONLY!!!!’

Question 27

how would you calculate initial rate of reaction

Answer 27

tangent from 0!! moldm^-3s^-1 units!

Question 28

how do you calculate rate for a rate equation

Answer 28

decrease/increase in a species divided by time duh…

Question 29

what mol value do you use when calculating delta H from q for a combustion reaction

Answer 29

the moles of FUEL

Question 30

how would you calculate bond enthalpy of eg 2.5 of a diatomic substance if a mean value for the bond has been given

Answer 30

just multiply the bond value by 2.5! multiply including the half!

Question 31

draw the boltzmann distribution curve at a higher vs lower temperature

Answer 31

Question 32

draw and label an energy profile diagram

Answer 32

Question 33

would changing temperature affect either the rate or the rate constant

Answer 33

yes, both and they will change in the same direction

Question 34

how can initial rate be studied using a clock reaction

Answer 34

the time taken for a visual change to occur is measured, initial rate is then taken to be proportional to 1/t it assumes that there is no significant change in the rate of reaction at the start compared to the time when taking the measurement and so the initial rate is an estimation when calculated this way

Question 35

how do you calculate Kp (like the step by step)

Answer 35

1. find equilibrium moles of each 2. find total moles 3. calculate mol fraction of each using these 4. find partial pressure of each by doing mol fraction x total pressure 5. sub partial pressures into Kp equation 6. find Kp units done!

Question 36

why is a reaction spontaneous

Answer 36

TdeltaS > deltaH so deltaG < O

Question 37

what mole value do you use when calculating deltaH of solution from Q

Answer 37

the moles of the thing that you are specifically calculating deltaH for

Question 38

between concentration-time graphs and rate-concentration graphs, which one show a line down, up, and flat

Answer 38

conc-time: down rate-conc: flat/up

Question 39

what is enthalpy change in terms of bond breaking and making

Answer 39

the energy released when forming bonds compared to the energy required when breaking bonds

Question 40

what are the enthalpy changes of combustion of elements within a compound equal to

Answer 40

the enthalpy changes of formation of their respective compounds when the og reacts with O2

Question 41

how is k calculated in a rate equation

Answer 41

sub in the rate values make sure to put them to the power show in the equation calculate the units for k

Question 42

how is an equation given to calculate bond enthalpies different to a normal one

Answer 42

everything is in a gaseous state rather than their standard states

Question 43

how can you make it so that the order concerning one reactant is zero when you’re trying to study the order of another reactant

Answer 43

use a large excess