Module 5 Chapter 18

Question 1

What is required for a reaction to take place

Answer 1

particles must collide before a reaction can take place

The reactants must possess at least the minimum amount of energy - activation energy

Particles must approach each other in a certain relative way - the STERIC EFFECT

Question 2

What is the rate of reaction proportional to

Answer 2

The concentration of a particular reactant raised to a power

Question 3

What is the power called

Answer 3

The order of the reaction for that reactant

Question 4

What are the powers for the different orders

Answer 4

N = 0 zero order
N = 1 first order
N = 2 second order

Question 5

What is order

Answer 5

The order attributed to a reagent identifies the effect changing its concentration has on rate of a reaction

Question 6

What is the rate constant k

Answer 6

It is a constant of proportionality that reflects the ease that a reaction takes place. Where larger values of k result in a greater rate of reaction.

Question 7

What does the continuous monitoring method allow

Answer 7

Data to be collected through the course of the reaction —> allowing data to be plotted on a. Concentration tie graph

Question 8

What does calorimetry allow

Answer 8

The measurement of the absorption of light passing through a coloured solution

Question 9

What can be done with the absorption of the coloured solution

Answer 9

A calibration curve made from known concentration can then be used to determine the concentration at a given time

Question 10

How is a calorimetry experiment done (1)

Answer 10

1. a reaction with an observable colour change must be used
2. You must then zero the colorimeter, in order to create a calibration curve. Which is done by using known concentrations of the species responsible for the observable colour change. Allowing you to convert absorbance readings into concentration readings later
3. Carry out the reaction between your reactants taking absorbance measurements at regular time intervals.

Question 11

How is a calorimetry experiment done (2)

Answer 11

Compare the absorbance values against the calibration curve from earlier - extrapolating the concentration at these times

Plot concentration against time, which can then be used to determine order of reaction

Question 12

What can you use concentration time graphs to determine

Answer 12

The rate from the gradient
The order from the shape of the curve

Question 13

What does a first order concentration time graph look like

Answer 13

It is a downward curve
Rate is decreasing

Question 14

What does a second order concentration time graph look like

Answer 14

Similar to the first order curve
But it starts steeper and tails of slower

Question 15

What is the half life of a reaction

Answer 15

The time it takes for the concentration to decrease by half

Question 16

What is a feature of the half life of a first order reaction

Answer 16

They have a constant half life and an exponential decay

Question 17

What is the formula you use to determine k for a first order reactant

Answer 17

k = ln2/t 1/2

Question 18

What is the rate concentration graph for a zero order reactant

Answer 18

DRAW IT

Question 19

What is the rate concentration graph for a first order reactant

Answer 19

DRAW IT

Question 20

What is the rate concentration graph for a second order reactant

Answer 20

Draw it

Question 21

What is the rate equivalent to for a zero order reactant

Answer 21

K

Question 22

What is the rate equivalent to for a first order reactant

Answer 22

Rate = k[A]

Question 23

What is the rate equivalent to for a second order reactant

Answer 23

Rate = k[A]^2

Question 24

What is a feature of the rate second order rate concentration graph

Answer 24

K can’t be determined from this graph unless it’s re plotted as rate against concentration squared

Question 25

What does an initial rates method record

Answer 25

The time it takes for a single easily recognisable change to occur early in the reaction e.g. - set volume of gas - colour change - precipitate formation

Question 26

What is assumed in initial rates methods

Answer 26

That the average rate of reaction = the initial, rate of reaction

Question 27

In the initial rates method what is the formula used to determine rate

Answer 27

Rate = 1/t T- time taken for change to occur 1 is used as an arbitrary point

Question 28

What is a iodine clock reaction

Answer 28

It is a reaction that can be undertaken using the formation of iodine; which forms a complex with starch to produce a blue-black colour change - indicating the completion of the reaction

Question 29

What is a feature of an iodine clock reaction

Answer 29

To do this, only the concentration of one reacts should change whilst the other factors that impact rate are kept constant

Question 30

What are the steps for an iodine clock reaction (1)

Answer 30

Reactants are mixed together in presence of another chemical such as sodium thiosulphate Na2S2O3 (aq) The time taken for the blue-black colour to appear is recorded and initial rates is calculated as 1/t A graph of 1/t is plotted against concentration allowing for visual identification of rate from the graph

Question 31

What are the steps for an iodine clock reaction (2)

Answer 31

Repeats are done with varied concentrations of the same reactant Further experiments are completed with changes in concentrations of other reactants From the orders with respect to each reactant can be determines and the rate equation written. Allowing the rate constant to be calculated

Question 32

What do the thiosulphate ions do in the iodine clock reaction

Answer 32

They are added to delay the time at which the colour change is observed as iodide ions are formed, preventing an immediate change in colour.

Question 33

How does an average rate become more accurate to the initial rate

Answer 33

The shorter the period of time over which an average rate is measured the less the rate changes over that period. So it will be closer to the initial rate.

Question 34

What is a feature of many reactions

Answer 34

They have mechanisms that require more than one step to complete

Question 35

What is the rate determining step

Answer 35

The slowest step is the one that determines the overall reaction rate as it is the step with the greatest activation energy

Question 36

What is a feature of the rate determining step (1)

Answer 36

Not all reactants are involved in the rate determining step and the particle numbers wont match the balanced equation.

Question 37

What is a feature of the rate determining step (2)

Answer 37

There is a direct relationship between the order and the rate determining step, so order relates to the moles involved.

Question 38

What does the Arrhenius equation explain

Answer 38

The effect of temperature on rate of reaction

Question 39

What is the Arrhenius equation

Answer 39

K = Ae ^(-Ea/RT) K = rate constant A = frequency factor Ea - activation factor R = gas constant T = temperature (kelvin)

Question 40

What does the exponential factor relate to

Answer 40

The number of particles that exceed the activation energy.

Question 41

What does the pre-exponential factor A mean

Answer 41

It is a measure of the frequency of collisions that occur.