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CHEMICAL REACTION ORDERS
I. ObjectiveStudents have skill to determine system reaction
order H+ and S2O3-.
II. Principle (Theory)Reaction order is the number of atom or
molecule that its concentration
determine reaction rate. Reaction order relate with
stoichiometry in phase that
determine reaction. But, rarely this phase that determine
reaction is described by
reaction equation in whole.
For first order reaction, reaction rate has straight proportion
withsubstance concentration that is being react and is asserted in
mathematic formula
as follow:
In this case, c = substance concentration that is being react, k
= reaction rate
constant, and reaction rate.In second order reaction, reaction
rate depends on square concentration. In
mathematic formula as follow:
So, forn order reaction is asserted as:
In other word, reaction rate has straight proportion with
reverse time or
proportion with concentration square n. So,
Reaction rate (times)-1 concentration
For first reaction order, graph reverse time toward
concentration produce
straight line. While, for second order reaction graph reverse
time toward square
concentration produce parabole line.
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III. Equipments and Materials Beaker glass 50 mL 2 pieces
Graduated cylinder glass 100 mL Graduated cylinder glass 10 mL
Stopwatch HCl solution 3 M Na2S2O3 solution 0,15 M Water
IV. Procedure1. Make mixtures from volumes reactan substances
like as table I. Formerly,
mix always sodium tiosulphate solution and water before add
chloride acid.
The
number of
Na2S2O3(mL)
The number
of H2O
(mL)
Concentration
of Na2S2O3(mL)
The number
of HCl
(mL)
25 - 0,15 4
20 5 0,12 4
15 10 0,09 4
10 15 0,06 4
5 20 0,03 42. Shake and stir the beaker glass until the mixture
is stirred quitely.3. Make a note of the time begin from acid is
added until muddy arise because
precipitate of sulphur. Doing this practice must be carefully.
Will be better if
this practice is done twice in minimal scale. Make a note about
the result.
4. Repeat again this practice according to table 2, where volume
of sodiumtiosulphate solution is made constant and volume of
chloride acid is varied.
The
number ofNa2S2O3
(mL)
The number
of H2O(mL)
Concentration
of HCl(mL)
The number
of HCl(mL)
25 - 3 5
25 2 1,8 3
25 4 0,6 1
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5. Make a note toward time and reverse time of sodium
tiosulphate solution.6. Determine order reaction toward sodium
tiosulphate solution.
V. Observing Result
Determine concentration ofNa2S2O3
a. There no adding of water so that not there dilution
reaction.b. 20 mL Na2S2O3 + 5 mL water
V1 x M1 = V2 x M2
20 x 0.15 = 25 x M2
3 = 25 M2
M2
= 0,12 Molar
c. 15 mLNa2S2O3 + 10 mL waterV1 x M1 = V2 x M2
15 x 0.15 = 25 x M2
2,25 = 25 M2
M2 = 0,09 Molar
d. 10 mL Na2S2O3 + 15 mL waterV1 x M1 = V2 x M2
10 x 0.15 = 25 x M2
1,5 s= 25 M2
M2 = 0,06 Molar
e. 5 mLNa2S2O3 + 20 mL waterV1 x M1 = V2 x M2
5 x 0.15 = 25 x M2
0,75 = 25 M2
M2 = 0,03 Molar
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Table 1 ( reaction between sodium tiosulfate and chloride
acid)
Table 1The
number of
Na2S2O3(mL)
The
number of
H2O(mL)
Concentration of
Na2S2O3(M)
The number
of HCl
(mL)
Reaction
Time
(s)
1/t
(s-1
)
25 - 0,15 4 7 0,14
20 5 0,12 4 9 0,11
15 10 0,09 4 14 0,07
10 15 0,06 4 27 0,05
5 20 0,03 4 46 0,02
Table 2
Thenumber of
Na2S2O3(mL)
The numberof H2O
(mL)
Concentrationof HCl
(M)
The numberof HCl
(mL)
ReactionTime
(s)
25 - 3 5 19
25 2 1,8 3 26
25 4 0,6 1 33
VI. Discussion
1. How are the reaction order toward to :a. Tiosulphateb.
Chloride acid
2. What can be stated to explain reaction order the
getting?3.
a. How is the reaction order toward to sodium tiosulphate if ion
concentrateis big ?
b. Can chemical reaction have a stage in overall?
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Answer :
Na2S2O3(aq) + HCl(aq) NaCl(aq) + SO2(aq) + S(s) + H2O(l)
1. Reaction orders to :
a. Tiosulfate
Vy
Vx=
nM
nM
HClOSONak
HClOSONak
][][
][][
322
322
(
)
(
)
()
(
)
So, the reaction orders of sodium tiosulfate is one.
b. HCl
y
x
V
V=
nM
nM
HClOSONak
HClOSONak
][][
][][
322
322
(
)
()
( )
1,36
Log 1,36 = n log 1,67
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n = log 1,36/log 1,67
n = 0,6
Total reaction orders is :
m + n = 1 + 0,6 = 1,6
2. To determine the reaction order of the reaction of a solution
is influenced bychange of concentration and time. We have to
compare the reaction rate with one
another reaction rate equal compare of concentration tiosulphate
(1 and 2) and
compare of concentration HCl (1 and 2).
y
x
V
V=
nM
nM
HClOSONak
HClOSONak
][][
][][
322
322
To get reaction orders of tiosulphate we have to use
concentration of HCl that
constant. And to get reaction orders of HCl we have to use
concentration of
HCl that constant.
3. a. If the concentration of tiosulfat is very big, reaction
orders is constant
because time will adjust with change of concentration.
b. Maybe it is depended with concentration and time of the
reaction.
VII. CommentIf we doing an experiment about reaction, we must be
doing be carefully. We
also observe in every changed was done. When we measure time
appear muddy,
we have to be carefully, because it is influence to determine
reaction orders.
VIII. Conclusion :To determine reaction orders is influenced by
change of concentration and time.
And to find reaction orders we have to using initial rates from
several
experiments.
