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a level chemistry > module 3+5: rates of reaction > Flashcards

module 3+5: rates of reaction Flashcards

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1
Q

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

A

order 0

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2
Q

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

A

order 1

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3
Q

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

A

order 2

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4
Q

how do you calculate the overall order

A

find the sum of the reactant’s orders

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5
Q

what equation is used with orders and the rate constant

A

.

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6
Q

how do you find the units for K

A

rate is: mol/dm³/s

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

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7
Q

what does this concentration-time graph show?

A

0 order

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8
Q

what does this concentration-time graph show?

A

1 order

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9
Q

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

A

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

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10
Q

what order does this rate-concentration graph show

A

order 0

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11
Q

what order does this rate-concentration graph show

A

first order

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12
Q

what order does this rate-concentration graph show

A

second order

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13
Q

what is the rate-determining step

A

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

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14
Q

what is the d-block

A

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

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15
Q

what are the elements of the arrhenius equation and units

A

.

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16
Q

how does pressure influence rate of reaction

A

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

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16
Q

how does surface area impact rate of reaction

A

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

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17
Q

how do catalysts affect reaction rate

A

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

18
Q

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

A

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

19
Q

define homogeneous catalysts

A

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

20
Q

define heterogeneous catalysts

A

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

21
Q

what are economic and sustainability advantages of catalysts

A
  • 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
22
Q

what is a half life

A

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

23
Q

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

A
  1. a collision is unlikely between more than 2 species
  2. the stoichiometry in the rate equation doesn’t match the overall equation
24
Q

define rate of reaction

A

the change in amount of reactant or product per unit time

25
Q

what does the line on a conentration-time graph represent

A

rate

26
Q

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

A

GASES ONLY!!!!’

27
Q

how would you calculate initial rate of reaction

A

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

28
Q

how do you calculate rate for a rate equation

A

decrease/increase in a species divided by time
duh…

29
Q

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

A

the moles of FUEL

30
Q

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

A

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

31
Q

draw the boltzmann distribution curve at a higher vs lower temperature

A
32
Q

draw and label an energy profile diagram

A
33
Q

would changing temperature affect either the rate or the rate constant

A

yes, both
and they will change in the same direction

34
Q

how can initial rate be studied using a clock reaction

A

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

35
Q

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

A
  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!
36
Q

why is a reaction spontaneous

A

TdeltaS > deltaH

so deltaG < O

37
Q

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

A

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

38
Q

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

A

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

39
Q

what is enthalpy change in terms of bond breaking and making

A

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

40
Q

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

A

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

41
Q

how is k calculated in a rate equation

A

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

42
Q

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

A

everything is in a gaseous state rather than their standard states

43
Q

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

A

use a large excess

a level chemistry (15 decks)

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