rates of reaction

Rates Of Reaction

Flow Of Learning

Meaning Of Rate Of Reaction

MEASUREMENT OF RATES OF REACTION:

·Plot graph of quantity of product / reactant against time·Calculate the average rate of reaction·Calculate the rate of reaction at the specific time from the graph.

EXPLANATION FOR THE RATE OF REACTION BASED ON COLLISION THEORY :

· Particle Size· Concentration· Temperature· Catalyst

-The meaning of Collision Theory.-To explain how each factor increases

Is proven by

·Experiment On Effect Of Surface Area·Experiment On Effect Of Concentration·Experiment On Effect Of Temperature·Experiment On Effect Of Catalyst

How KFC can cook Fried chicken in quickly?

Application of The Rate Of reaction In daily Activities

Rate Of Reaction

Observable changes in quantity that use to

determine rate of reaction

Meaning rate of reaction

Unit for rate of reaction

Measurement

Rate Of Reaction

Avarage rate of reaction

Rate Of reaction at specific time

Factors that affect rate of reaction

Rate

• Speed = total Distance/Total time

J.B

K.L

Speed= Speed=

=

= 300km/h

=

= 100km/h

ChemicalChemical

Reaction TypesReaction Types

Bonds are made / broken Change in oxidation states Plasma

Bonds are made / broken Change in oxidation states Plasma

P+1 P+1

21

Li +1

Chemical properties/ changes/ reactions (i.e., reactivity, combustibility). development of a gas, formation of precipitate, and change in color).

Chemical properties/ changes/ reactions (i.e., reactivity, combustibility). development of a gas, formation of precipitate, and change in color).

Reactivity

Combustibility

Gas formation

Precipitate

Color change

• Hydrogen-VERY reactive.• Helium-Non-reactive.

The speeds of reactions are very varied• Rusting is a ‘slow’ reaction, you hardly see any

change looking at it! • The weathering of rocks is an extremely very

slow reaction.

weathering of rocks

The fermentation of sugar to alcohol is quite slow but you can see the carbon dioxide bubbles forming in the 'froth' in a laboratory experiment or beer making in industry!

Bubble gas

•A faster reaction example is magnesium reacting with hydrochloric acid to form magnesium chloride and hydrogen or the even faster reaction between sodium and water to form sodium hydroxide.

•Combustion reactions e.g. when a fuel burns in air or oxygen, is a very fast reaction.

CombustibilityThe tendency to react with Oxygen, releasing heat.

O2

BURNING

evidence of Chemical Change: development of a gas formation of precipitate change in color

evidence of Chemical Change: development of a gas formation of precipitate change in color

Meaning Of Rate Of Reactions

• The rate of reaction is a measurement of the change in the quantity of reactant or product against time:

Rate Of Reaction= Change in quantity of reactant / product Time taken

Student ans: Changes of reactant or product against time (0 Mark)

Meaning Of Rate Of Reaction

• A rate of reaction is high if the reaction occurs fast within a short period of time..

• A rate of reaction is low if the reaction occurs slowly within a long period of time..

• A rate of reaction is inversely proportional to time:

Rate of reaction α 1 time taken

Meaning Of Rate Of Reactions• The Higher rate of

reaction the shorter time taken to complete the reaction

• The lower rate of reaction the longer time taken to complete reaction

granule powder

5 minute 1 minute Which is the higher rate of reaction?

CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + H2O + CO2 (g)

Observable Changes Measurement Of Reaction

Changes of mass Rate of reaction =

= Z gs-

CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + H2O + CO2 (g)

Observable Changes

Measurement Of Reaction

Changes of volume

Rate of reaction =

= Z cm3s-

The change in amount of reactant / product that can be measured :•Decrease in total quantity of mass / concentration of the reactant per unit of time.•Increase in total amount of mass / concentration of the product of reaction per unit of time •Total volume of the gas released.•Formation of precipitate.

Observable changes

Decrease in total quantity of mass / concentration of the reactant per unit of time.

Increase in total amount of mass / concentration of the product of reaction per unit of time

Total volume of the gas released.CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + H2O + CO2 (g)

waterburette

Delivery tubeConical flask

Must shade!

Formation of precipitate.

Na2SO3+2HCl→NaCl+S+SO2+H20PERCIPITATE

stopwatch

Precipitate the formation of insoluble ionic compounds.

Precipitate the formation of insoluble ionic compounds.

Does NOT dissolve in water.

Example:Study the reaction: Between calcium carbonate and excess 1 mol dm-3 hydrochloride acid.CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + H2O + CO2 (g)

Mass of CaCO3

(g)

time (s)

Concentration of HCl (mole dm-3)

time (s)

CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + H2O + CO2 (g)

Concentration of CaCl2

(mole dm-3)

time (s)

Volume of CO2

(cm3)

time (s)

CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + H2O + CO2 (g)Observable changes

stopwatch

CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + H2O + CO2 (g)Observable changes

Hydrometer

CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + H2O + CO2 (g)Observable changes

Hydrometer

CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + H2O + CO2 (g)Observable changes

Displacement Of water

Remember !!!

•Quantities of reactant will decreases against time•Quantities of product will increases against time

CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + H2O + CO2 (g)

Measurement Rate Of Reaction Two ways to measure rate of reaction.1. Average Rate Of Reaction. : It is determined by calculating the total amount of reactant used or the total amount of product formed in a specific time.2. Rate Of Reaction at a specific time :It is determined by calculating the gradient of the graph at the time.

Introduction to the Rate of Reaction1. A reaction between small pieces of excess

calcium carbonate with 80 cm3 hydrochloric acid 0.05M is conducted a laboratory to study the rate of reaction at interval time. The volume of gas released is recorded in the table below.

Time (seconds) 0 30 60 90 120 150 180 210 240Burette reading (cm3) 49.5 33.5 23.5 16.0 10.5 5.0 2.0 2.0 2.0

40

30

40

30

37.00cm3 27.00cm3

Volume : 37-27=10 cm3

(a)Draw an apparatus to shows how this experiment can be conducted at laboratory.

Must label the diagram!

x

x

√

√

√

√

(b)Write a balance chemical equation for this reaction.

CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + H2O + CO2 (g)

(c)CaCO3 + 2HCl → CaCl2 + H2O + CO2

CaCO3 + 2H++2Cl- → Ca2++2Cl- + H2O + CO2

CaCO3 + 2H++ → Ca2++ H2O + CO2

Remember !!!Only separate soluble salt

Don’t separate covalent and

insoluble salt

(d)

Carbon dioxide gas

(e)A reaction between small pieces of excess calcium carbonate with 80 cm3 hydrochloric acid 0.05M is conducted a laboratory to study the rate of reaction at interval time.

Number of mole in the solution will use :

Mol, n

=

MV

1000

0.05(80)

1000

=

= 0.004 mol

(f)CaCO3 + 2HCl → CaCl2 + H2O + CO2

From the chemical equation :

Mole Ratios:

2 mol HCl : 1 mol CO2

0.004 mol HCl : 0.004 mol HCl

2 mol HCl

× 1 mol CO2

= 0.002 mol CO2

Volume of gas Co2 at room condition

= 0.002×24

0.048 dm3=

(g)

Because some of carbon dioxide gas can escape to surrounding during the experiment.

(h)Time (seconds) 0 30 60 90 120 150 180 210 240Burette reading (cm3) 49.5 33.5 23.5 16.0 10.5 5.0 2.0 2.0 2.0Volume CO2 (cm3) 0 16 26 33.5 39 44.5 47.5 47.5 47.5

Time(second) 0 30 60 90 120

Burette reading(cm3)

x49.5

y33.5

z23.5

Total volume of gas(cm3)

x-x0.00

x-y16.00

x-z26.00

0 30 60 90 120 150 180 210 240 2700

5

10

15

20

25

30

35

40

45

50

Volume of CO2, cm3

Time , s

Connect the point without using ruler!Not all the point is connected

0 30 60 90 120 150 180 210 240 2700

5

10

15

20

25

30

35

40

45

50

Volume of CO2 cm3

Time s

Cannot like this graphStraight line

It’s must be smooth graph

Average Rate Of reaction

The average rate of reaction in the first 90 seconds.

= The total volume of gas released in the first 90 secondsTime taken

(i)

Time (seconds) 0 30 60 90 120 150 180 210 240Burette reading (cm3) 49.5 33.5 23.5 16.0 10.5 5.0 2.0 2.0 2.0Volume CO2 (cm3) 0 16 26 33.5 39 44.5 47.5 47.5 47.5

=

33.5÷90=0.372 cm3s-1

Not cm3 per second

unit

i(ii)Time (seconds) 0 30 60 90 120 150 180 210 240Burette reading (cm3) 49.5 33.5 23.5 16.0 10.5 5.0 2.0 2.0 2.0Volume CO2 (cm3) 0 16 26 33.5 39 44.5 47.5 47.5 47.5

47.5÷180= 0.264 cm3s-1

The average rate of reaction in the whole experiment.

= The total volume of gas released in the whole experiment Time taken

=

(h)Volume of gas against time

y xαHow to fit your scale in graph?

For y: use ratio 5: 10 Check it’s enough by 5÷10=0.5

Maximum volume 47.5÷0.5=95 small boxes

How about x:?30÷10=3

Maximum 240÷3=80 small boxes

Total volume of Hydrogen gas/cm3

Time (second)

Analysis of Data

t

p

q

Rate of reaction at t second = gradient AB

= p/q cm3 s-1

A

B

Tangent

Cannot take directly at x

Tangent is a line that touch just 1 point of graph in order to calculate gradient

Tangent

Only touch 1 point of curve

Cannot touch more than 2 point because each of point have different gradient

0 30 60 90 120 150 180 210 240 2700

5

10

15

20

25

30

35

40

45

50

Same length

α

Same angle degree

tangentα

Total Volume of CO2(cm3)

Time (second)

Analysis of data

A

B

C

D

E

F

t1 t3t2

Rate of reaction at t1 = gradient AB

Rate of reaction at t2 = gradient CD

Rate of reaction at t3 = gradient EF

Each of point have different gradient!

Two method to calculate tangent:

Total volume of Hydrogen gas/cm3

Time (second)

A

B

Tangent

number of small

boxes × value of 1 small unit box

Y

X

Total volume of Hydrogen gas/cm3

Time (second)

A

B

Tangent

Gradient of graph:

m = ΔY

ΔX

x1 x2

y2

y1

m = Y2-y1

X2-x1

First Method

Total volume of Hydrogen gas/cm3

Time (second)

Analysis of Data

t

p

q

Rate of reaction at t second = gradient AB

= p/q cm3 s-1

A

B

Tangent

Total Volume of CO2(cm3)

Time (second)

Analysis of data

A

B

C

D

E

F

t1 t3t2

Rate of reaction at t1 = gradient AB

Rate of reaction at t2 = gradient CD

Rate of reaction at t3 = gradient EF

From the answer of question (i) (iii) and (i) (iv), make a conclusion from the calculation of this experiment.

(j)

Ans : Rate of reaction will decreases

(k)Explain why does there is a difference of the rate of reaction at 30 second and 120 second.

Ans: Rate of reaction at 30 second is higher because number of particles of reactant is higher than 120 second

(l)

In your opinion, what will happen to the rate of reaction if, •The concentration of acid is increased. •A calcium carbonate powder is used in this experiment.•The volume of acid is increased.•The temperature of acid is increased.•A bigger conical flask is used. •The conical flask containing acid is shaken.