Chapter 18

Question 1

How are reaction rates measured?

Answer 1

Observing the changes in the quantities of reactants/products over time

Question 2

rate =

Answer 2

quantity reacted or produced/time

change in concentration/change in time

Question 3

What units is concentration measured in?

Answer 3

mol dm-3

Question 4

What do square brackets represent?

Answer 4

Concentration

Question 5

What does [A] mean?

Answer 5

Concentration of A

Question 6

What units does [A] have?

Answer 6

mol dm⁻³

Question 7

What does changing concentration change?

Answer 7

Rate of a reaction

Question 8

What is rate of reaction proportional to?

Answer 8

The concentration of a particular reactant raised to a power

Question 9

rate ∝

Answer 9

[A]ⁿ

Question 10

What is n in rate ∝ [A]ⁿ?

Answer 10

Order of reaction

Question 11

What are some of the common orders?

Answer 11

1) zero order (0)
2) first order (1)
3) second order (2)

Question 12

What is zero order?

Answer 12

1) concentration of a reactant has no effect on the rate

2) rate ∝ [A]⁰

Question 13

What is first order?

Answer 13

1) rate depends on concentration raised to the power of 1

2) rate ∝ [A]¹

Question 14

What is second order?

Answer 14

1) rate depends on concentration raised to the power of 2

2) rate ∝ [A]²

Question 15

What is the rate equation?

Answer 15

The mathematical relationship between the concentrations of the reactants and the reaction rate.

Question 16

What is the rate constant, k?

Answer 16

1) proportionality constant

2) converts between the rate of reaction and concentration and orders

Question 17

overall order =

Answer 17

sum of orders with respect to each reactant

Question 18

What is the overall order for the rate equation rate = k[A]ᵐ[B]ⁿ

Answer 18

m+n

Question 19

What does ∝ mean?

Answer 19

proportional to

Question 20

Simplify the rate equation rate = k[A]⁰[B]¹[C]²

Answer 20

rate = k[B][C]²

Question 21

What do the units of the rate constant depend on?

Answer 21

The number of concentration terms in the rate equation

Question 22

How can you determine the units of the rate constant, k?

Answer 22

1) rearrange equation to make k the subject
2) substitute units into the expression for k
3) cancel common units and show the final units on a single line

Question 23

How are orders of reaction determined?

Answer 23

Experimentally by monitoring how a physical quantity changes over time

Question 24

What is continuous monitoring?

Answer 24

Plotting graphs from continuous measurements taken during the course of a reaction

Question 25

Give some methods of continuous monitoring that produce a gas as one of the products?

Answer 25

1) monitoring by gas collection | 2) monitoring by mass loss

Question 26

What can be used to estimate a colour change?

Answer 26

A colorimeter

Question 27

What is the gradient of a concentration-time graph?

Answer 27

Rate of reaction

Question 28

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

Answer 28

1) straight line | 2) negative gradient

Question 29

Does the reaction rate of a zero order reaction ever change?

Answer 29

No

Question 30

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

Answer 30

1) downward curve | 2) decreasing gradient

Question 31

What is constant in a first order reaction?

Answer 31

1) half-life | 3) the time for the concentration to halve

Question 32

What is the shape of a second order concentration-time graph?

Answer 32

1) downward curve | 2) decreasing gradient

Question 33

What is half life?

Answer 33

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

Question 34

What is exponential decay?

Answer 34

The concentration of a first order reaction halving every half life

Question 35

How can you determine k for a first order reaction?

Answer 35

1) from the rate | 2) from the half-life

Question 36

What is the formula to calculate the rate constant from the half-life?

Answer 36

k = ln2 / t₁/₂

Question 37

Why is it more accurate to use the formula for calculating the rate constant than drawing a tangent?

Answer 37

It is always difficult to judge how steep the tangent should be drawn.

Question 38

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

Answer 38

1) horizontal straight-line | 2) zero gradient

Question 39

What is the rate equation for a zero order reaction?

Answer 39

``` rate = k[A]⁰ rate = k ```

Question 40

What is the shape of a first order rate-concentration graph?

Answer 40

1) straight line graph through the origin | 2) positive gradient

Question 41

What is the rate equation for a first order reaction?

Answer 41

``` rate = k[A]¹ rate = k[A] ```

Question 42

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

Answer 42

1) upward curve | 2) increasing gradient

Question 43

What is the rate equation for a second order reaction?

Answer 43

rate = k[A]²

Question 44

Why can you not directly obtain the rate constant of a second order rate-concentration graph?

Answer 44

The rate-concentration graph is a curve

Question 45

How do you calculate the rate constant of a second order reaction?

Answer 45

By calculating the gradient of a graph of the rate against the concentration squared

Question 46

What is the initial rate?

Answer 46

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

Question 47

How can initial rate be found?

Answer 47

By measuring the gradient of a tangent drawn at t = 0 on a concentration-time graph

Question 48

What is a clock reaction?

Answer 48

1) takes a single measurement | 2) time t from the star of an experiment is measured for a visual change to be observed, often a colour or precipitate

Question 49

What is the initial rate of a clock reaction?

Answer 49

initial rate ∝ 1/t

Question 50

How is a clock reaction repeated?

Answer 50

With different concentrations

Question 51

What colour is aqueous iodine?

Answer 51

Orange-brown

Question 52

What happens when starch is added to iodine

Answer 52

It forms a complex with iodine which is an intense dark blue-black colour

Question 53

Describe how the order of a reaction can be determined from the shape of a rate-concentration graph.

Answer 53

1) 0 order is a horizontal line 2) 1st order is a straight line. starting at the origin 3) 2nd order is an upward curve, starting at the origin

Question 54

What does a colorimeter measure?

Answer 54

1) the intensity of light passing through a sample | 2) absorbance (directly linked to the concentration of the solution)

Question 55

How is the filter for a colorimeter chosen?

Answer 55

So that it is the complimentary colour to the colour being absorbed in the reaction

Question 56

When can a reaction only take place?

Answer 56

When particles collide

Question 57

What is a reaction mechanism?

Answer 57

The series of steps that make up an overall reaction

Question 58

What is the rate-determining step?

Answer 58

The slowest step in the sequence

Question 59

What does the rate equation only include?

Answer 59

Reacting species involved in the rate determining step

Question 60

What do the orders in the rate equation match?

Answer 60

The number of species involved in the rate-determining step

Question 61

What are haloalkanes hydrolysed by?

Answer 61

Hot aqueous alkali

Question 62

What happens as temperature increases?

Answer 62

1) rate increases | 2) value of the rate constant k increases

Question 63

Increasing temperature shifts the Boltzmann distribution to what side?

Answer 63

Right, increasing the proportion of particles that exceed the activation energy Eₐ

Question 64

What is the Arrhenius equation?

Answer 64

1) an exponential relationship between the rate constant k and temperature T 2) k - Ae⁻ᴱᵃ/ᴿᵀ

Question 65

What is A in the Arrhenius equation?

Answer 65

Pre-exponential factor (frequency factor)

Question 66

What is -Eₐ/RT in the Arrhenius equation?

Answer 66

Exponential factor (linked to activation energy and temperature)

Question 67

What is R in the Arrhenius equation?

Answer 67

Gas constant - 8.314Jmol⁻¹K⁻¹

Question 68

What is T in the Arrhenius equation?

Answer 68

Temperature in Kelvin