Chapter 1

1.1 1.1 RATE OF REACTIONRATE OF REACTION

Why a tall building can be destroyed Why a tall building can be destroyed with explosives within seconds??with explosives within seconds??

Why food has to take several hours Why food has to take several hours

to be decay ?? to be decay ??

Why do coal mines face a high risk Why do coal mines face a high risk of explosion ??of explosion ??

All these are because :All these are because :difference of difference of

rate of reactionrate of reaction

What is the rate of reaction ?

The speed at which reactants are converted into products in a

chemical reaction

For examples:

1. Fireworks display occurs in just a few seconds

Rate of reaction HIGH

2. The photosynthesis process takes a few hours

Rate of reaction LOWER

3. The erosion process of stones takes many years

Rate of reaction VERY LOW

Some reactions are fast & some reactions are very slow

So do the chemical reactions in laboratory

How we determine & calculate the rate of chemical reactions

in laboratory ??

It just same with the way we calculate the speed of driving

How we calculate the

speed of driving ??

Yes, the formulae is :

Speed = distance (km) time (hour)

In the other hand, it is :

Rate of = physical changesreaction time

What are the changes that we could measure??

Mass before and after experiment (gs-1)Colour changesTemperature changes (°Cs-1)Pressure changes (Ps-1)Volume of gas liberated (cm3

s-1) (only if the reaction produce gases)

A + B C + D

(reactants) (products)

During the chemical reaction, reactants will become less but products become more

Decomposition of hydrogen peroxide to form water and oxygen gas

H2O2 (aq) H2O (l) + O2 (g)

For any chemical reaction, we can measure its

average rate of reaction & rate of reaction at a given time

Rate of = physical changesreaction time

average rate of reaction

rate of reaction at a given time

Average rate = total changesof reaction total time taken

Rate of reaction at a given time = gradient of the curve at that instant= y2 – y1 / X2 – X1

Volume of hydrogen gas ( cm3 )

Time ( s )

Total changes

Total time taken

Average rate = total changesof reaction total time taken


Time ( s )

Changes = y2 – y1

time taken = X2 – X1

Rate of reaction at 90 second = gradient of the curve at that instant

= y2 – y1 / x2 – x1

1. find the given time2. draw a line to curve3. draw a tangent4. Measure y2 – y1

5. Measure x2 – x1

Let’s see an example:

burette

water

Hydrochloric acid

Marblechips

Hydrogengas

CaCO3 + HCl CaCl2 + H2O + H2

Volume of hydrogen gas was recorded every 30 seconds

. . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . after 10 minutes . . .

Here’s the result :

Time / s

Reading of burette

/ cm3

Volume of gas/ cm3

Then we plot the graph: Volume of hydrogen gas ( cm3 )

Time ( s )

5

10

0

35

30

25

20

15

6030 90

180210

240270

300150

120

Get the answers:

a) Calculate the average rate of reaction between marble chips and hydrochloric acid.

Solution: refer to table

Time / s

Reading of burette

/ cm3

Volume of gas/ cm3

Average rate of reaction = total changes / total time taken

Average rate of reaction = 34 cm3

300 s

= 0.113 cm3 s-1

** you’ll get the same answer by using graph

b) Calculate the average rate of reaction in the first 90 seconds.

Solution:

Time / s

Reading of burette

/ cm3

Volume of gas/ cm3

this is accumulated !!

Average rate of reaction = total changes / total time taken

Average rate of reaction = 20 cm3

90 s

= 0.222 cm3 s-1

** you’ll get the same answer by using graph

c) Calculate the rate of reaction at

a) 60 second

b) 210 second

5

10

35

30

25

20

15

Time ( s )

90


060

30180

210240

270300

150120

Solution (a) :

22.00 – 10.50= 11.50 cm3

90-30 = 60 s

Rate of reaction at 60 second

= y2 – y1

x2 - x1

= 22.00 -10.50

90 -30

= 11.50 cm3

60 s

= 0.192 cm3 s-1 **

5

10

35

30

25

20

15

Time ( s )

90


060

30180

210240

270300

150120

Solution (b) :

35.50 – 30.00= 5.50 cm3

255-160 = 95 s

Rate of reaction at 210 second

= 35.50 -30.00

255 -160

= 5.50 cm3

95 s

= 0.058 cm3 s-1 **

d) Compare the rate of reaction at

60 second and 210 second

Solution:Rate of reaction at 60 second = 0.192 cm3 s-1

Rate of reaction at 210 second = 0.058 cm3 s-1

- The rate of reaction at 60 second is higher than 210 second.

- This means the reaction occurs faster at the moment of 60 second

e) Why the rate of reaction at 60 second is higher than 210 second ?

Solution:

- Because the concentration of reactants is decreasing during the chemical reaction.

f) There are no more hydrogen gas liberated after 300 second, why?

Solution:- Because the chemical reaction is

stopped- All the marble chips had been reacted

Rate of reactionvery high

Rate of reaction

lower

Curve becomes horizontal lineNo more reaction occur

Rate of reaction = 0 cm3 s-1

Rate of reaction

More lower

Total volumeof gas

Liberated (cm3)

Time (s / min)

Learning Task 1.2page 8

Some reactions are fast & some reactions are very slow

So do the chemical reactions in laboratory

What are the factors affect the

rate of reaction ??

2. Temperature

1. Total surface area

4. Catalyst5. Pressure

3. Concentration

2T 2C 1P

How does the factors ofTotal surface area,

Temperature, Concentration,

Catalyst & Pressure

affect the reaction rate??

2T

2C

1P

Let’s do the experiment to investigate that:

1.Surface area smaller , rate of reaction2.Concentration higher, rate of reaction3.Temperature higher, rate of reaction4.Catalyst added, rate of reaction

Surface area smaller , rate of reactionConcentration higher, rate of reactionTemperature higher, rate of reactionCatalyst added, rate of reactionPressure higher, rate of reaction

Problem solving

A + B C + D

(reactants) (products)

- During the chemical reaction, reactants will become less but products become more

- The chemical reaction will stop once one of the reactants is used up.

Pattern of graphs

Reactant A + Reactant B gases

Less Less More

Mg (s) + HCl (aq) Mg (s) + HCl (aq) MgCl (aq) + H MgCl (aq) + H22 (g) (g)excess

Draw out the curves of graph for:1. Magnesium mass / 2. Hydrochloric acid concentration/ 3. Magnesium chloride concentration /4. Hydrogen gas volume against the time

1. the curves of graph for Magnesium mass against the time

Magnesium Excess

>>>

2. the curves of graph for hydrochloric acid concentration

against the time

Hydrochloric acidLimited reactant

3. the curves of graph for magnesium chloride concentration

against the time

Hydrochloric acid has been used up &

reaction stopped

4. the curves of graph for hydrogen gas volume against the time

Hydrochloric acid has been used up &

reaction stopped

Q1. Compare these:Set 1 : 1g of zinc plate (excess) reacts

with sulphuric acid 0.1 mol dm-3 to form zinc sulphate and hydrogen gas

Set 2 : 1g of zinc powder (excess) reacts with sulphuric acid 0.1 mol dm-3 to form zinc sulphate and hydrogen gas

Find the difference !!

Hydrogen Gas / cm3

Time / s

Set 2

Set 1The number of moles

of chemical subtances are same

Factor : total of surface area /

Particle size

Q2. Compare these:Set 3 : 1 g of zinc powder (excess) reacts

with 500cm3 sulphuric acid 0.1 mol dm-3 to form zinc sulphate and hydrogen gas

Set 4 : 1 g of zinc powder (excess) reacts with 250cm3 sulphuric acid 0.2 mol dm-3 to form zinc sulphate and hydrogen gas


Hydrogen Gas / cm3

Time / s

Set 4

Set 3The number of moles

of chemical subtances are same

Factor : Concentration

Hydrogen Gas / cm3

Time / s

Set 6

Set 5

The number of moles of chemical subtances

are same


Hydrogen Gas / cm3

Time / s

Set 8

Set 7

The number of moles of chemical subtances

in Set 8 is higher, so the volume of gas

realeased is higher


Find out what they means!!CollisionCorrect orientation Activation energyEffective collisionCollision frequencyEffective collision frequencyEnergy profile diagram

Achieve effective collision

Base on kinetic theory, particles moves constantly and collide each other all the time

However, majority of collisions do not lead to a reaction,why ?

Only those in which the colliding species have:

Achieve minimum amount of energy, called the ACTIVATION ENERGY, Ea

And with CORRECT ORIENTATION

EFFECTIVE COLLISIONS

For a reaction to take place, the particles of the substances that are reacting have to collide. If they collide, with enough energy then they will react.

The minimum amount of energy that particles need to react is called the ACTIVATION ENERGY

Activation energyActivation energy

therefore some main ways of increasing the rate of a reaction:

1) increase the number of collisions2) increase the amount of kinetic energy so that more collisions lead to a reaction3) decrease the energy activation so that more reactants could be reacted

what factors could cause 1, 2, 3?

Size of solid reactant smallerTotal surface area exposed to collision

with other reactant particle is biggerThe frequency of collision between

reactant particles increaseFrequency of effective collision increaseRate of reaction higher

Higher temperatureHigher temperatureKinetic energy of reactant particles increaseKinetic energy of reactant particles increaseParticles move faster and collide more oftenParticles move faster and collide more oftenThe frequency of collision between

reactant particles increaseFrequency of effective collision increaseRate of reaction higher

Higher concentrationMore number of particle per unit volume of

solutionThe frequency of collision between

reactant particles increaseFrequency of effective collision

increaseRate of reaction higher

Positive catalyst usedenables the reaction occur through an

alternative path which requires lower activation energy

More colliding particles are able to achieve the lower activation energy

Frequency of effective collision increase

Rate of reaction higher

Activationenergy Lower

Activationenergy

Higher pressureMore number of particle per unit volume

of solutionThe frequency of collision between

reactant particles increaseFrequency of effective collision

increaseRate of reaction higher

Conclusion

Chapter 1

Education

Transcript of Chapter 1