Brainscape's Knowledge GenomeTM

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


See full index

A Level Chemistry > Chapter 18 - Rates of reactions > Flashcards

Chapter 18 - Rates of reactions Flashcards

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

How do you calculate the rate of a reaction?

A

Change in concentration / time

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

What are the usual units of rate?

A

mol dm^-3 s^-1

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

What are the usual units for concentration?

A

mol dm^-3

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

How do you write concentration using shorthand?

A

[A]

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

What is the rate of reaction proportional to?

A

The concentration of a particular reactant raised to the order it has

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the three main orders a reaction can have?

A

Zero, first and second

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

When will a reactant have zero order?

A

When changing its concentration has no impact on the rate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is important to remember about a zero order reaction?

A

Anything raised to the power of zero is 1

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

When will a reaction have first order?

A

When the rate of reaction depends on the concentration of a reactant raised to the power 1

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

When will a reaction have second order?

A

When the rate of reaction depends on the concentration of a reactant raised to the power 2

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

What does the rate equation tell you?

A

The mathematical relationship between the concentrations of reactants and the rate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the rate equation?

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is k?

A

The rate constant

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the overall order of a reaction?

A

The sum of the orders of all the reactants

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

Can you determine the rate of a reaction using chemical equations?

A

No, it must be determined experimentally

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the initial rate of a reaction?

A

The instantaneous rate at the beginning of a reaction when t=0

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

How would you measure the order of a reactant?

A

Conduct an experiment using a set concentration of the reactant
Record the rate at regular intervals
Conduct the experiment identically but using a different concentration of the reactant
Compare your measurements for the rate of reaction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

How do you work out the units for k?

A

Rearrange the equation to make k the subject
Substitute units in for your readings
Cancel common units and display the final unit on one line

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What are the two main methods of continuous monitoring?

A

Gas collection and mass lost

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

How do you measure the rate of reaction using a colour change?

A

Set the colourimeter to the wavelength of light you’re investigating
Calibrate the colourimeter using distilled water and set the absorbance to zero
Take samples from your reaction mixture at regular intervals and measure the absorbance of each one using the colourimeter

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is the shape of the concentration-time graph for a zero order reaction?

A

A straight line with a constant, negative gradient

22
Q

What is the shape of the concentration-time graph for a first order reaction?

A

A downward curve with a decreasing gradient

23
Q

How do you identify k for a zero order reaction?

A

It is the gradient of the line

24
Q

How do you identify k for a first order reaction?

A

Use the half-life, which should be constant

25
Q

What is the half-life?

A

The time taken for half of a reactant to be used up

26
Q

How can you identify a first-order reaction using half lives?

A

The half-life will always be constant

27
Q

What pattern does half life follow?

A

Exponential decay

28
Q

What is the equation for calculating k using half-life?

A

k = ln(2) / half life

29
Q

How do you calculate k using a graph?

A

Draw a tangent at a point
Record the concentration and rate
Use the equation k = rate / concentration

30
Q

What is the shape of the rate-concentration graph for a zero order reaction?

A

A horizontal line with the gradient 0

The y-intercept gives the value of k

31
Q

What is the shape of the rate-concentration graph for a first order reaction and why?

A

A single straight line through the origin
The rate is proportional to the concentration
K is the gradient

32
Q

What is the shape of the rate-concentration graph for a second order reaction?

A

An upward curve with increasing gradient

33
Q

How do you determine k from the rate-concentration graph for a second order reaction?

A

Plot the second graph of rate against concentration squared

The gradient of this straight line is k

34
Q

How can a clock reaction be used to measure the rate?

A

The time is measured from the beginning of the reaction for a precipitate to form

35
Q

How do you calculate the initial rate using a clock reaction?

A

1 / time taken for visual change to occur

36
Q

How does an iodine clock work?

A

The time taken for the iodine to form (a red-brown colour) is recorded

37
Q

What assumptions do we make when using clock reactions?

A

The concentration of the reactant doesn’t change significantly over the time period of the reaction
The temperature stays constant
When the endpoint is seen, the reaction has not proceeded too far

38
Q

Reasons why it is unlikely that a reaction will occur in a single step

A

Too many atoms of reactants need to collide

The atoms are unlikely to collide with the correct orientation

39
Q

What is the reaction mechanism?

A

The series of steps that make up the overall reaction

40
Q

What is the slowest step in a reaction called?

A

The rate-determining step

41
Q

How are haloalkanes hydrolysed and how can this help us?

A

They are hydrolysed with hot, aqueous alkali and they can help us t identify the rate-determining step

42
Q

How is the order of a reactant used in the rate determining step?

A

The order of a reaction with respect to a reactant shows the number of molecules of that reactant which are involved in the rate-determining step

43
Q

How can you predict the rate-determining step?

A

The rate equation only involves species included in the rate-determining step
The orders in the rate equation match the numbers of species in the rate-determining step

44
Q

What impact will increasing the temperature by 10c have on the rate constant and the rate of reaction?

A

In general, it doubles them

45
Q

Why does the rate constant increase with temperature?

A

There are more particles with sufficient energy to react

Particles collide faster and more frequently

46
Q

What is the Arrhenius equation?

A

k = A x ^-Ea/RT

47
Q

What does A stand for in the Arrhenius equation?

A

A pre-exponential factor

48
Q

What is T measured in for the Arrhenius equation?

A

K

49
Q

What does e^-Ea/RT represent?

A

The proportion of molecules that have sufficient energy to react

50
Q

What is the logarithmic form of the Arrhenius equation?

A

ln(k) = -Ea/RT + ln(A)

51
Q

How can the logarithmic form of the Arrhenius equation be turned into y=mx+c?

A 
y = ln(k)
m = -Ea/RT
x = 1/T
c = ln(A)

A Level Chemistry (29 decks)

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