Experiment # 9: Chemical Equilibrium MAB2, Group # 9, Ma’am Leah Rubio
GENTOLIA, Michal Consuela C. March 22, 2010
TORREMANA, Cyrille Stephanie J.
Chemical equilibrium is the state reached by a certain reaction mixture when the rates of forward and
backward reaction have become equal. In dynamic equilibrium the forward and backwards reactions continue at
equal rates so the overall effect does not change. On a molecular scale there is continuous change. On the
macroscopic scale nothing appears to be happening. The system needs to be closed – isolated from the outside
world. Nothing can be added to the system or taken away from it apart from energy. It is very important to be
knowledgeable about this topic since it is vital for these reactions and mixtures to maintain equilibrium at all
times. There are applications of chemical equilibrium in real-life, and these are vital as well. In Experiment No. 9,
different reagents were added to the Fe(NO3)3 and KCNS mixture. There were five reagents that were added
namely 0.1 M Fe(NO3)3, 0.1 M KCNS, 0.1 M KCl, 0.1 M AgNO3 and NaF crystals. Distilled water was also added
to the mixture to serve as a reference to the latter mixtures. The change in temperature was also executed when
two test tubes were subjected to heat and ice separately. The effects were observed to see whether there has
been a forward or a backward shift under different conditions.
Keywords: shift, equilibrium, pressure, temperature, concentration, system
Introduction means of food preservation that do not involve
changes in temperature, maintains chemical
A chemical reaction is in equilibrium when equilibrium in the foods and thereby prevents or at
there is no tendency for the quantities of reactants least retards spoilage. Even more important is the
and products to change. If there have been maintenance of equilibrium in reactions between
observable changes taking place like change in hemoglobin and oxygen in human blood.
color, release of gas bubbles, appearance of
precipitate, or even the release of heat, one should
bear in mind that the reaction is not yet at Experimental
equilibrium. Though this is the case, one should
also note that it doesn’t necessarily mean that the For this experiment, we used the following
reaction is at equilibrium if there is no apparent apparatus: 10 mm x 100 mm Test Tubes, 100-mL
change. The equilibrium state is one in which no beakers, spot plates and alcohol lamps. We also
change in composition take place, and no energetic used the following reagents: 0.1M Fe(NO3)3, 0.1M
tendency is present for further change. KCNS, 0.1M KCl, 0.1M AgNO3. We also used NaF
crystals and ice water.
The Le Chatelier’s Principle states that
when a system in equilibrium is disturbed by a We combined 20 drops of 1 M Fe(NO3)3
change of temperature, pressure, or concentration with 20 drops of 1 M KCNS solutions in a test tube.
variable, the system shifts in equilibrium Having this solution, we placed 10 drops of it to the
composition in a way that tends to counteract this six spots in the spot plate. On the first spot, we
change of variable added another 10 drops of distilled water which
served as the reference. We added 5 drops each of
The addition of reagents in this experiment 0.1 M Fe(NO3)3 to the second spot, 0.1 M KCNS to
serves as the bombardment in the reaction that is the third spot, 0.1 M KCl to the fourth spot, 0.1 M
already been in an equilibrium state. The changes AgNO3 to the fifth spot and a pinch of NaF crystals
that will arise from this will be able to help in to the sixth spot.
determining the shift.
In two separate test tubes labeled as test
Chemical equilibrium is very vital and tube 7 & 8, we added ten drops of distilled water.
observable with issues concerning human health. Ice water was prepared on a 50-ml beaker where
The cooling of food with refrigerators, along with test tube 7 was placed. After dipping test tube 7, it
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Chem 14.1, Chemical Equilibrium
was compared to the solution in the first spot. On After adding 5 drops of 0.1 M KCl, the
the other hand, test tube 8 was heated over low solution had white precipitate and was yellowish in
flame. It was also compared to test tube 1 color. The solution became oil-like and eventually
immediately after heating. turned to white upon the addition of the NaF
These processes allowed us to determine
the directions of shift for each reaction. After dipping test tube 7 in the prepared ice
water, the color we observed was lighter than the
reference’s color. However, it should be darker than
Result the reference’s color.
REAGENT / DIRECTION When test tube 8 was compared to the
TREATMENT OF SHIFT reference after heating, there was no significant
0.1 M Darker Forward change except for the appearance of bubbles.
Fe(NO3)3 However, the color should be lighter than the color
0.1 M KCNS Super Darker Forward of the reference.
0.1 M KCl Red No shift
* No change There are conditions that affect the balance
0.1 M AgNO3 White Backward of the equilibrium – Pressure, Temperature and
precipitate and Concentration.
color If the pressure is increased, the equilibrium
Pinch of NaF “Oil-like” at first Backward will shift to reduce the pressure, meaning it will
Clear move to the side with the least number of gaseous
Increase in Lighter Forward moles. On the other hand, if the pressure is
Temp * Darker decreased, the equilibrium will move in the direction
Decrease in Appearance of Backward that increases the number of gaseous moles.
SAME If there is a forward increase in
* Lighter temperature, the reaction is exothermic. On the
other hand, if there is a backward decrease in
temperature, the reaction is endothermic. In
Discussion summary, high temperature is equated to lots of
reactant while low temperature is equated to lots of
After adding distilled water to the Fe(NO3)3 products.
and KCNS solution, the color of the mixture became
light red orange. This served as the reference for By adding one of the ingredients that go to
the comparison of color of the succeeding solutions. make up the reaction, the concentration changes,
thus making the equilibrium act to shift reaction
Five other reagents were added separately such that the amount of added material is reduced.
to the Fe(NO3)3 and KCNS solution.
Adding a catalyst in a reaction does not
When the 0.1M Fe(NO3)3 was added, the make any difference to the position of equilibrium,
color of the mixture became darker compared to and Le Chatelier's Principle doesn't apply to them.
that of the reference mixture.
When 0.1M KCNS was added, the mixture Guide Questions & Answers
was very darker than that of the reference. It
seemed blackish or dark bluish. 1. Explain your observations on the basis of
Le Chatelier’s Principle.
The solution turned red when there was an
addition of 0.1M KCl. However, there should have Le Chatelier’s principle states that if a
been no change in color compared to the reference dynamic equilibrium is disturbed by
mixture. changing the conditions, the position of
equilibrium moves to counteract the
change. The experiment, based on this
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Chem 14.1, Chemical Equilibrium
principle, has undergone a lot of changes in References
condition which explains the change in the
shifts of the reactions. Upon addition of (n.d.) Chemical equilibrium. Retrieved March 12,
reagents, there were visible changes in the 2010 from
color of Fe(NO3)3, KCNS, AgNO3, and NaF http://library.thinkquest.org/10429/low/equil/equbod
because there was a change in the y.htm
concentration. Having the ice water and the
addition of heat, there were also (n.d.) Chemical equilibria. Retrieved March 14,
remarkable changes in their colors which 2010 from
explains the change in temperature that isa http://www.webchem.net/notes/how_far/equilibria/c
based on Le Chatelier’s principle. hemical_equilibria.htm
2. Which species (ions) in the added reagents Clark, Jim. (2002). Le Chatelier’s principle.
are effective in altering the state of the Retrieved March 13, 2010 from
There were four reagents that had
observable shifts. These are NaF, AgNO3, Clark, Jim. (2002). An introduction to chemical
KCNS and Fe(NO3)3. In the case of NaF, equilibria. Retrieved March 13, 2010 from
since both are not present in the given http://www.chemguide.co.uk/physical/equilibria/intro
mixture, sodium and fluorine ions contribute duction.html#top
in altering the state of the system. For
AgNO3, silver has caused the shift to occur. Lower, S. (2010, Jan. 7). Chemical equilibrium
In the case of the two other reagents, they introduction: Reaction that goes both ways.
have also caused the alteration because of Retrieved March 12, 2010 from
the additional moles since they are also http://www.chem1.com/acad/webtext/chemeq/Eq-
present in the given mixture. 01.html#SEC2
3. Is the reaction endothermic or exothermic?
With the addition of heat, there is visible I hereby certify that I have given substantial
increase in temperature and notable contribution to this report.
change in the color of the solution,
therefore, the reaction is exothermic.
GENTOLIA, Michal Consuela C.
Conclusion & Recommendations
Based on the data gathered from the
experiment, we therefore conclude that TORREMANA, Cyrille Stephanie J.
concentration, pressure and temperature are
factors that contribute in the shift of direction that
will enable the mixture to go back to its equilibrium.
Some of our observations are different from
that of what should have been observed, especially
during the part wherein temperature has been
changed. We recommend that those who will be
conducting this experiment should be vigilant
enough that they try to follow the procedures as
keen as possible. The deviations from the
theoretical results might have been caused by
some errors during the experiment itself.
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Chem 14.1, Chemical Equilibrium