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

Experiment On Effect Of Surface Area
Experiment On Effect Of Concentration
Experiment On Effect Of Temperature
Experiment On Effect Of Catalyst
Is proven by

How KFC can cook Fried chicken in quickly?

Application of The Rate Of reaction In daily Activities

Observable changes in quantity that use to determine rate of reaction
Meaning rate of reaction
Unit for rate of reaction
Avarage rate of reaction
Measurement
Rate Of Reaction
Rate Of reaction at specific time
Factors that affect rate of reaction
Rate Of Reaction

Rate
Speed = total Distance/Total time
K.L
J.B

Speed=
Speed=
=
=
= 100km/h
= 300km/h

Reaction Types
2
1
Chemical
Bonds are made / broken
Change in oxidation states
Plasma
Li
+1
P+1
P+1

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 hydrogenor 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.

Combustibility
The tendency to react with Oxygen, releasing heat.
O2
BURNING

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
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.

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.
Deliverytube
Conical flask
burette
water
Must shade!

Formation of precipitate.
Na2SO3+2HCl->NaCl+S+SO2+H20
PERCIPITATE
stopwatch

Precipitatethe 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)

Observable changes
stopwatch

Observable changes
Hydrometer

Observable changes
CaCO3 (s) + 2HCl (aq) -> CaCl2(aq) + H2O + CO2 (g)
Displacement Of water

Remember !!!
Quantities of reactant will decreases against time
Quantities of product will increases against time

Measurement Rate Of Reaction
Two ways to measure rate of reaction.
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.
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 Reaction
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.

40
40
30
30
27.00cm3
37.00cm3
Volume : 37-27=10 cm3

(a)
Draw an apparatus to shows how this experiment
can be conducted at laboratory.
Must label the diagram!

√
√

(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 covalentand insoluble salt

(d)
Carbon dioxide gas

(e)
A reaction between small pieces of excess calcium carbonate with 80 cm3hydrochloric acid 0.05M is conducted a laboratory to study the rate of reaction at interval time.
Number of mole in the solution will use :
MV
Mol, n
=
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
×
1 mol CO2
2 mol HCl
=
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.

Volume of CO2, cm3
Connect the point without using ruler!
Not all the point is connected
Time , s

Volume of CO2 cm3
Cannot like this graph
Straight line
It’s must be smooth graph
Time s

(i)
Average Rate Of reaction
The average rate of reaction in the first 90 seconds.
= The total volume of gas released in the first 90 seconds
Time taken
33.5÷90=0.372 cm3s-1
unit
=
Not cm3 per second

i(ii)
The average rate of reaction in the whole experiment.
= The total volume of gas released in the whole experiment
Time taken
47.5÷180= 0.264cm3s-1
=

(h)
Volume of gas against time
y
x
α
How 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=80small boxes

Analysis of Data
Rate of reaction at t second = gradient AB
= p/q cm3 s-1
Total volume of Hydrogen gas/cm3
Tangent is a line that touch just 1 point of graph in order to calculate gradient
B
Tangent
p
A
q
Cannot take directly at x
t
Time (second)

Tangent
Cannot touch more than 2 point because each of point have different gradient
Only touch 1 point of curve

tangent
α

Analysis of data
Total Volume of CO2(cm3)
F
D
E
Rate of reaction at t1 = gradient AB
B
Rate of reaction at t2 = gradient CD
C
Rate of reaction at t3 = gradient EF
Each of point have different gradient!
A
t1
t3
t2
Time (second)

Two method to calculate tangent:
number of small boxes ×value of
1 small unit box
B
Tangent
Y
A
X
Time (second)

First Method
Gradient of graph:
m = ΔY
ΔX
B
m = Y2-y1
y2
X2-x1
Tangent
A
y1
Time (second)
x1
x2

Analysis of Data
Rate of reaction at t second = gradient AB
= p/q cm3 s-1
B
Tangent
p
A
q
t
Time (second)

Analysis of data
Total Volume of CO2(cm3)
F
D
E
Rate of reaction at t1 = gradient AB
B
Rate of reaction at t2 = gradient CD
C
Rate of reaction at t3 = gradient EF
A
t1
t3
t2
Time (second)

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.

Rates of reaction

by rudi_z on May 15, 2011

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