Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Module 5 Chemistry > Chapter 18 - Rates of reaction > Flashcards

Chapter 18 - Rates of reaction Flashcards

You may prefer our related Brainscape-certified flashcards:
Periodic Table flashcards Chemistry 101 flashcards AP® Chemistry flashcards Organic Chemistry 101 flashcards
1
Q

what is the rate of a reaction

A

rate of reaction is the change in concentration of products or reactants per unit time

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what is the generalised equation for rate of reaction

A

rate of reaction = Change in Conc./time

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what are the units for rate of reaction

what is the shorthand for concentration

A

moldm^-3s^-1

[A]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what are the 4 factors on the rate of a reaction

what is the important proportionality regarding one of these

A
  • temperature
  • surface area
  • catalyst
  • concentration

Rate is directly proportional to [A] ^ n
where n is the order of the reaction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what is meant by a zero order reaction

A

rate direct prop. [A]^0

  • concentration has no effect on rate
  • n = 0
  • concentration doubles = rate stays the same
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what is meant by a first order reaction

A

rate direct prop. [A]^1

  • concentration is directly proportional to rate
  • n = a
  • concentration doubles, rate doubles
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what is a second order reaction

A

rate direct prop. [A]^2

  • concentration^2 is directly proportional to rate
  • n = 2
  • concentration doubles, rate quadruples
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what is the rate equation for a reaction and how can you calculate the overall order

A

Rate = k [A]^n [B]^m

overall order = n+m

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

how can we calculate the units for the rate constant

A

rearrange for k
write out units

moldm^-3s^-1/(moldm^-3)^n+m

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

how can you find the order of reaction from experimental data

A

1) observe how the rate changes when the conc. of one reactant increases (whilst keeping all other conc.’s constant)
2) repeat for other reactants

quote data in answers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what is a continuous monitoring method and what does it measure

A
  • gives information on how the rate of reaction changes throughout the reaction
  • measures a property which is constantly changing
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what is an initial rates method and what do we need to be careful of

A
  • gives information on how the initial rate varies as the starting concentration of a reactant changes
  • it can be inaccurate because the ROR at the start is not always the same as all the way through
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what are the 4 main ways to measure rate of reaction and how can we do them, what types of measuring are they

A
  • measure volume or mass of gas produced, use an upturned measuring cylinder or measure loss of mass over time using a mass balance, continuous method
  • track the formation of a precipitate, time how long it takes for a precipitate to obscure a mark - initial
  • measure changes in pH using a pH metre - continuous
  • use a colorimeter - measures the absorbance of a particular wavelength of light by a solution, continuous
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what does the gradient of a concentration-time graph represent

A

rate of reaction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what does a concentration-time graph look like for a zero order reaction/its features

A
  • straight negative gradient line
  • ROR never changes with concentration so grad doesn’t change
  • gradient = k
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what does a concentration-time graph look like for a first order reaction/its features

A
  • downwards curve with flattening curve over time
  • ROR slows with time so gradient becomes less -ve
  • constant half life, time for conc. of reactant to half is constant
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

what does a concentration-time graph look like for a second order reaction/its features

A
  • same as shape for first order but steeper and tails off slower
18
Q

what is a half life

A

“the half life, t1/2, is the time taken for the concentration of a reactant to halve”

19
Q

how can we find half-life from a first order reaction

A
  • first order reactions have a constant half-life
  • measure successive periods where the concentration of the reactant has halved
  • if they are the same then the time period value is the half life and the reaction must be first order
20
Q

what are the two ways of determining k from a first order reaction

A
  • drawing a tangent

- using half life

21
Q

how can we use the tangent to calculate k from a first order concentration time graph

A
  • draw a tangent at a point
  • measure its gradient, this is rate
  • determine the value for conc. at the point the tangent touches the line
  • substitute to rate = k[A]^n
22
Q

how can we use the half life of a first order reaction to find k

A

k = ln(2)/(t1/2)

23
Q

what do the lines for 0th, 1st and 2nd order reaction look like on a concentration-rate graph

A

0th = flat line, rate does not change with concentration

1st = straight line up, rate does not change with concentration

2nd = quadratic style curve

24
Q

what are the features of 0th order line on a concentration-rate graph

A 
Grad = 0
rate = k
Y-intercept = k
25
Q

what are the features of 1st order line on a concentration-rate graph

A 
rate = k[A]
y = mx
k = gradient
26
Q

what are the features of 2nd order line on a concentration-rate graph

A

rate = k[A]^2
so if you plot rate-concentration^2
gradient = k

27
Q

what is the alternative way of drawing rate-concentration graphs to avoid any of the issues

A

log-log graphs
rate = k[A]^n
log(rate) = nlog[A] + log(k)
y = mx+c

28
Q

what is the initial rates method and what is a clock reaction

A
  • the initial rate is the instantaneous rate when t = 0
  • this can be found through the gradient of the tangent on a concentration-time graph when t = 0
  • clock reactions measure the time from the start of the experiment to the point where a visual change is observed
  • we assume there’s no significant change in rate and model
    Rate direct prop 1/T
  • this is repeated for different concs
29
Q

what is the iodine clock reaction

A
  • clock reactions use iodine’s reaction with starch to provide a clear colour change
  • make a reaction that produces iodine
  • add sodium thiosulphate and starch
  • as the iodine is formed it immediately reacts with the thiosulphate
  • once all the thiosulphate is used up, the starch/iodine solution goes blue-black and this is the end point
30
Q

how are reactions with more than 2 reactants likely to occur

A

with more than one step/stage of reaction

31
Q

define the rate determining step

A

“The rate determining step (the one which decides the overall rate) is the slowest step”

32
Q

what are the 3 main consequences of the rate determining step

A
  • increasing the concentration of any reactant that is not in the rate determining step has no effect - they have an order of 0
  • only the reactants in the rate determining step are in the rate equation
  • the molar quantities of the rate determining step correspond to their orders in the rate equation
33
Q

how can we form a mechanism from the rate equation

A

1) identify reactants of the rate determining step using the rate equation
2) identify stoichiometry
3) predict products
4) predict other step

  • combining the equations must reform the initial equation
  • equations must balance
  • species and molar ratios must agree with the rate equation
34
Q

what occurs in many cases where there is a 10 degree rise in temperature for a reaction

A

rate doubles

35
Q

what are the factors that affect the rate constant and how do they affect it

A
  • temperature, higher temperatures mean more particles have greater than (or equal to) the activation energy, particles are also more likely to collide
  • Ea, a lower Ea gives more particles able to react

the dominant factor is Ea and proportion of particles greater than Ea

36
Q

what is the arrhenius equation and units

A

k = Ae^(-Ea/RT)
activation energy = J
temperature = K

37
Q

what do the pre-exponential and exponential factor determine in the arrhenius equation

A

Pre-exponential factor = takes into account orientation

exponential factor = proportion of molecules greater than Ea

38
Q

how can we also write the arrhenius equation which is a more useful way

A 
K = Ae^(-Ea/RT)
ln(k) = (-Ea/R)(1/T) + ln(A)
y = mx+c
39
Q

why might a reactant have an order of effectively 0 even if it is in the equation

A

it is in excess

40
Q

what should we remember when rearranging a rate equation to calculate concentrations

A
  • watch out for squares/cubes in the powers

- easiest way to realise is to rearrange fully and not take short cuts

Module 5 Chemistry (6 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions