Rates of Reaction

Question 1

Define rate of reaction

Answer 1

The change in concentration per unit time.

Question 2

What units does rate of reaction have?

Answer 2

Mol¹Dm⁻³S⁻¹

Question 3

What does the order of reaction indicate?

Answer 3

Reaction orders indicate how changing the concentration of a reactant affects the rate of reaction.

Question 4

Describe how a zero order reactant would affect the rate of reaction

Answer 4

The concentration of the reactant has no effect on the rate of reaction.

Question 5

Describe how the concentration of a first order reactant changes the rate of reaction

Answer 5

A first order reactant’s concentration is directly proportional to the rate of reaction.

Question 6

Describe how the rate of reaction changes with the he concentration of a second order reactant

Answer 6

The rate of reaction is proportional to the square of the reactants concentration.

Question 7

If a second order reactants concentration is tripled what whappens to the rate of reaction?

Answer 7

Increases by 9x

Question 8

If a first order reactants concentration is doubled what happens to the rate of reaction?

Answer 8

The rate of reaction also doubles

Question 9

What is the rate constant K?

Answer 9

The rate constant k is the proportionality constant, relating the concentration of reactants to the rate of reaction.

Question 10

What does the overall order show and how is it calculated?

Answer 10

The overall order shows the overall affect of concentrations on the rate of reaction. It can be calculated by adding the reaction orders/ powers of the reactants. (m+n).

Question 11

Define continuous monitoring

Answer 11

Continuous measurements taken over the course of a reaction.

Question 12

For a concentration time graph what shape does zero order make?

Answer 12

Straight line with a constant negative gradient.

Question 13

For a concentration time graph what shape does the first order make?

Answer 13

Downward curve with the gradient getting close to 0 as time increases.

Question 14

How can concentration time graphs be plotted?

Answer 14

Using data from continuous monitoring.

Question 15

How can the reaction rate be found using a concentration time graph?

Answer 15

Find the gradient of the concentration time graph.

Question 16

Define half life

Answer 16

The time taken for half of the reactant to be used up.

Question 17

What sort of half life do first order reactions have?

Answer 17

A constant half life (exponential decay)

Question 18

How can the half life of a first order reactant be found on a concentration time graph?

Answer 18

Measure the time taken for the concentration to half.

Question 19

How can a concentration time graph be shown as first order?

Answer 19

Each succesive half life should be the same.

Question 20

What is the equation for calulating rate constant from half life?

Answer 20

K=ln2/t

t is half life

Question 21

For a Rate-Concentration gaph what is the shape of a zero order reactant.

Answer 21

Straight horizontal line with no gradient.

Question 22

For a Rate-Concentration gaph what is the shape of a first order reactant.

Answer 22

Straight line with a gradient starting at the origin.

Question 23

How is the rate or reaction found from a first order reaction?

Answer 23

Find the gradient of the rate concentration graph.

Question 24

What is the initial rate?

Answer 24

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

Question 25

How is a Rate concentration graph fromed from clock reactions (e.g. iodine clock)?

Answer 25

-Starting at a low concentration, the time taken for the brown/orange colour of aqeous iodine is measured.
-This is then repeated increasing the concentrations whilst still measuring the time.
-Once finished a table is made with concentrations and their times, with an additional column for 1/t.
-A graph is then modelled with 1/t (rate) against concentration using the concentration and 1/t values from the table.

Question 26

Why can 1/t be used as rate, in a rate concentration graph?

Answer 26

1/t is proportional to rate.

Question 27

Monitoring rate with a colorimeter is an exmaple of a “ “ method used to find reaction rates

Answer 27

Continuous monitoring

Question 28

chemical clocks is an exmple of using “ “ to find reaction rates?

Answer 28

Initial rates

Question 29

using chemical clocks to find out reaction rates is an “ “

the accuracy

Answer 29

approximate

Question 30

Describe the process of measing reactions rates (producing a concentration time graph) by colorimetry
(e.g. Iodine)

Answer 30

1.A light source is set up aswell as a filter to control the wavelength of light passing through the solution, behind the filter is a colorimeter to measure the absorbance of light.

2.Place water between the filter and colorimeter and zero the colorimeter.
3.Measure the absorbance readings of a solution of varying concentrations (e.g. iodine) , producing an absorbance concentration graph.

4.Add a reactant (propanone) to a solution and then measure the absorbance at timed intervals.

5.Plot a concentration time graph using the absorbance time measurements from 4 but replacing abosrobance values with concentration values from 3.

Question 31

What is the rate constant?

Answer 31

k

Question 32

What is the rate determining step?

Answer 32

Slowest step of a multi step process, only includes reactants from the rate equation.

Question 33

Why does increased temperature also increase the rate of reaction/rate constant.

Answer 33

-Increased temperature shifts the Boltzman distribution to the right, therefore more particles exceed or have the activation energy Eₐ needed to react.

-There is an increase in the amaount aof particle collsions as the particles move faster and collide more often.

Question 34

In the Arrhenius equation what is the relationship between K and T

Answer 34

Exponential relationship between k and t

Question 35

What must be done to the arrhenius equation before graphing to find Ea and A ( dont explain how to get A or Eₐ)

Answer 35

Ln both sides to get the equation Ln k = Eₐ/RT + Ln A
making a graph of ln K against 1/t.

Question 36

How can A be found from a
ln K and 1/T graph

Answer 36

Find the y intercept to get ln A and then put the value of ln A to the e.
eˡⁿ ᵃ

Question 37

How can Eₐ be found from a ln k against 1/t graph?

Answer 37

find the gradient to get -Eₐ/R
then multiple the gradient by -R, or -8.314