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Chemistry 12 > Unit 2.5 > Flashcards

Unit 2.5 Flashcards

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1
Q

reaction rate

A

change in concentration of a reactant or product per unit time

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2
Q

rate as time goes on

A

should decrease and be as close to 0 as possible (reaction is “finished”)

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3
Q

instantaneous rate vs. average rate

A

average rate: just the slope of the change in reactant over time

instantaneous rate: shows rate at a certain point in time

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4
Q

rate law

A

shows how the rate depends on the concentrations of reactants

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5
Q

why don’t products appear in the rate law?

A

the concentrations of the products do not appear in the rate law because the reaction rate is being studied under conditions where the reverse reaction does not contribute to the overall rate

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6
Q

integrated rate law

A

shows how concentration depend on time

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7
Q

how to measure the rate of reaction of a gas

A
  • water displacement measures the volume of H2/ the rate that the volume changes is equal to the rate that the moles change which can give you the concentration/time
  • with concentration measuring probes
  • can measure the rate that the mass of a solution goes down by a scale
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8
Q

how to measure rate of reaction when solid is the limiting reagent

A

measures the mass/time which can be moles/ time

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9
Q

how to measure rate of reaction when acid/base

A

measure pH to translate to concentration of H+. as the concentration of H+ shows how much more acidic/basic a solution is getting

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10
Q

how to measure rate of reaction when coloured compound

A

measure the rate that the colour disappears/appears (qualitative) or measure using a colorimeter

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11
Q

how to measure rate of reaction when opaque

A

this is also relative using the disappearing cross experiment

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12
Q

rate of appearance/disappearance

A

when calculating the rate of change of the reactants disappearing, a negative sign is added to make the rate positive

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13
Q

how does rate of reaction make sense

A

10 mol/s means 10 moles of reactions occur each second, not that 10 moles of chemical actually react. 6.02 x 10^23 times molecules number of reactions

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14
Q

k

A

contains al the factors such as temperature, steric factor, reactivity etc. and the units can vary

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15
Q

order

A

shows how much of an effect changing the concentration of one variable has on the rate

ex. order 2 is doubled
= quadrupled reaction

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16
Q

overall order

A

sum of the exponents. a higher total order means more dependent/sensitive reaction to concentration

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17
Q

when given the concentration of a reactant and the eqn

A

don’t multiply the concentration by the coefficient!

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18
Q

initial rate

A

the initial rate at which the reactants combine

experimentally: measure the instantaneous rate at t=0

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19
Q

nuclear decay

A

first order reaction

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20
Q

collision theory

A

molecules must collide to react however majority of collisions do not lead to a reaction

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21
Q

collision theory concentration

A

rate increases as the concentration of reactants increase

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22
Q

transition state/activated complex

A

bonds go through a transition state. the species at the transition state is called the activated complex. this is very unstable

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23
Q

activation energy

A

reactants must collide with enough energy to form the activated complex

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24
Q

temperature

A

at high temperature means that the molecules have a greater average kinetic energy which means the collision will have more energy to overcome the activation energy

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25
Q

steric factor

A

A, a number that represents the likelihood that a collision occurs with the right geometry.

decreasing the size, increases the rate of reaction
increases the surface area available for collisions to take place

26
Q

reaction mechanism

A

the process by which a reaction occurs

27
Q

each collision in a mechanism is called

A

elementary step

28
Q

elementary steps

A
  • can be uni or bimolecular (1 or 2 molecules reacting)
29
Q

rate determining step

A

the slowest elementary step determines the rate of the overall reaction
- the order is the coefficient since each reactant is the coefficient

30
Q

a valid mechanism

A
  1. sum of elementary steps must give the overall reaction
  2. the rate law based on the RDS must be consistent with the experimental rate law
  3. no elementary step includes more than 2 reactants
31
Q

intermediate

A

generated in a reaction and reactant in a subsequent one (c)

A+B –> C
C + D –> E +

32
Q

catalyst

A

reactant of a reaction and regenerated in a subsequent one

A+B –> C
C + D –> E + A

33
Q

phase

A

one phase: no distinguishable substance

two phases: looks like two things mixed together

34
Q

Heterogeneous catalysis

A

This involves the use of a catalyst in a different phase from the reactants. Typical examples involve a solid catalyst with the reactants as either liquids or gases.

One or more of the reactants are adsorbed on to the surface of the catalyst at active sites.

An active site is a part of the surface which is particularly good at adsorbing things and helping them to react.

enzyme weakens the bonds or interacts with the surface

then the molecule is desorbed

35
Q

adsorption

A

Adsorption is where something sticks to a surface

36
Q

desorbtion

A

Desorption simply means that the product molecules break away. This leaves the active site available for a new set of molecules to attach to and react.

37
Q

good Heterogeneous catalysis

A

adsorbs pretty well but not strongly enough to not be able to desorb

38
Q

catalytic converters

A

Catalytic converters change poisonous molecules like carbon monoxide and various nitrogen oxides in car exhausts into more harmless molecules like carbon dioxide and nitrogen using expensive metals. can be affected by catalyst poisoning

39
Q

catalyst poisoning

A

this happens when something which isn’t a part of the reaction gets very strongly adsorbed onto the surface of the catalyst, preventing the normal reactants from reaching it.

40
Q

Homogeneous catalysis

A

catalyst is in the same phase as the reactants. Typically everything will be present as a gas or contained in a single liquid phase.

41
Q

homogeneous catalysis examples

A

The destruction of atmospheric ozone by CFCs is an example of homogeneous catalysis.

42
Q

each collision is called

A

elementary step. sum of this equals the overall reaction

43
Q

elementary steps and rate law

A

you can use coefficients of the rate determining step since the order for that is the coefficients.

the rate of reaction is equal to rate of RDS

44
Q

valid mechanism

A

1) sum of steps must equal overall rxn
2) rate law based on RDS must equal experimental law
3) no elementary steps can include more than 2 reactants (can’t be more than bimolecular)

45
Q

intermediate

A

generated in reaction and is a reactant in another one

46
Q

catalyst

A

used in beginning and comes out at the end: not in overall

47
Q

intermediate and reaction mechanisms

A

if there is an intermediate in the RDS, you must substitute it in the rate law with what it depends on to be vlalid

48
Q

for reaction to occur

A

molecules must collide with the right reactants, orientation and energy greater than the activation energy

rate is proportional to the # of collisions times the % of successful collisions

49
Q

high temperature

A

high # of collisions as more kinetic energy therefore more successful collisions (ratio is same) strongest effect on rate

50
Q

catalyst

A

high % of successful collisions, lowers activation energy which means high number of collisions with Energy greater than activation energy

51
Q

high surface area

A

more # of collisions since more reactant is exposed

52
Q

chemical nature of elements

A

a higher K means a higher rate than others. this K means that some chemicals are more reactive than others and will react faster

53
Q

high reactant concentration

A

of collisions is high since more moles = more collisions between reaction states

54
Q

activated complex

A

species in transition state that is unstable (has all bonds formed)

55
Q

smaller size of particles

A

higher rate since its higher surface area for collisions to occur

56
Q

maxwell botlzman

A

higher temperature means that there is a lower peak on the distribution

a greater spread/ variance means overall greater average energy

Ea is a point on the x-axis and the area under the distribution past the Ea is the proportion of molecules that will react

57
Q

unimolecular vs bimolecular

A

uni is 1H2

bimo is 2H2

uni has no intermediate

bio has 1 intermediate and 2 transition states

58
Q

a good catalyst

A

adsorbs well but not too well that it can’t desorb

59
Q

draw out the reaction progress with a positive delta H

A

this should have a high p and low r

60
Q

raw out the reaction progress with a negative delta H

A

this should have a low R and a high P

61
Q

high order

A

means more sensitive to concentration

62
Q

how to tell order based on uniter

A

look at K

Chemistry 12 (6 decks)

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