CHEMICAL EQUILIBRIUM | Chemical Equilibrium | Solution

CHEMICAL EQUILIBRIUM Jelly Jane Buhay Dessa Jean Casalme Deane Allison Catapang Janis Mary Cayabyab De La Salle University-Dasmariñas Dasmariñas, Cavite Philippines ABSTRACT The experiment entitled “Chemical Equilibrium” aims to help students study the basics in chemical equilibrium and to help them investigate the effects of varying the temperature and concentration of reactants in equilibrium reactions. A chemical equilibrium is a system in which two opposing reactions proceed at the same rate. When a chemical reaction takes place at a

container which prevents the entry or escape of any of the substances involved in the reaction, the quantities of these components change as some are consumed and others are formed. Eventually this change will come to an end, after which the composition will remain unchanged as long as the system remains undisturbed. In this experiment, we dissolved a pinch of Na2CrO4 crystals in distilled water and added a drop of 6M HCl. Then the solution is divided into two parts, the first was added with 12.5 mL water and the other with 5 drops of 6M NH4OH. Then we mixed 8 mL of 0.1M BaCl2, with distilled water in the three test tubes. They were added with drops of reagents and the results were compared. The color of the solution when Na2CrO4 was dissolved in water was yellow. Then the color of the solution when added with 6M HCl turned to orange. Upon the dilution with in water with four times the solution’s volume, the mixture gained yellow color. And upon the addition of 6M NH4OH solution, the mixture turned to a yellow orange color. The effect of decreased HCl concentration on the equilibrium was the generation of more of it. The equilibrium will shift backward in a reaction producing more HCl molecules. When Na2CrO4 solution was added with 6M NH4OH, the solution’s color turned yellow orange. This means that equilibrium rate of forward and backward reactions were met.

INTRODUCTION Chemical equilibrium is the state in which a chemical reaction proceeds at the same rate as its reverse reaction; the rates of the forward and reverse reactions are equal, and the concentration of the reactants and products stop changing. When this condition was met, there was no change in the proportions of the various compounds involved, and the reaction ceases to progress. A common example given is the Haber-Bosch process, in which hydrogen and nitrogen combine to form ammonia. Equilibrium is reached when the rate of production of ammonia equals its rate of decomposition. Le Chatelier's principle describes qualitative predictions that can be made about chemical equilibrium. Without energy input chemical reactions always proceed towards equilibrium. Chemical equilibrium, a condition in the course of a reversible chemical reaction in which no net change in the amounts of reactants and products occurs. A reversible chemical reaction is one in which the products, as soon as they are formed, react to produce the original reactants. At equilibrium, the two opposing reactions go on at equal rates, orvelocities, hence there is no net change in the amounts of substances involved. At this point the reaction may be considered to be

completed; i.e., for some specified reaction condition, the maximum conversion of reactants to products has been attained.

METHODOLOGY To test the effects of concentration, a pinch of Na2CrO4 crystals was dissolved in 5 mL distilled water. A drop of 6M HCl was added, was shaken and the color was noted. The acidified solution was divided into two parts. In the first portion, 12.5 mL water was added. To the other, 5 drops of 6M NH4OH was added. The colors of the mixtures of each portion were noted. In the application of the law of chemical equilibrium to solubility equilibrium, 8 mL of 0.1M BaCl was mixed with 8 mL of distilled water and equal portions was placed in 3 test tubes. To tube #1, 0.3 ml (6 to 7 drops) of 0.5M H2C2O4 was added; and to tube #2, 0.6 ml (10 drops) of 6M HCl was added and mixed. The new mixture was referred to as tube #3. To this the same solution, a slight excess of 6M NH4OH was added and mixed. This mixture was the tube #4. RESULTS AND DISCUSSIONS A. Effects of Concentration Color of Solution when Na2CrO4 is dissolved in H2O: Color when 6 M HCl is added:

YELLOW ORANGE

Acid Solutions of Na2CrO4:

1. Color upon dilution with four times its volume of water. 2. Color upon addition of 6 M NH4OH solution.

YELLOW YELLOW ORANGE

B. Application of the Law of Chemical Equilibrium to Solubility Equilibrium Solutions Mixed

Observation

BaCl2 + H2C2O4

Clear white

BaCl2 + Na2C2O4

Cloudy white; immiscible

Tube #1 + 6M HCl (Tube #3)

Clear white

Tube #3 + 6M NH4OH

No precipitate formed

Table 1 Data and Results on the Application of the Law of Chemical Equilibrium to Solubility Equilibrium

The color of the solution when Na2CrO4 was dissolved in water was yellow. Then the color of the solution when added with 6M HCl turned to orange. Upon the dilution with in water with four times the solution’s volume, the mixture gained yellow color. And upon the addition of 6M NH4OH solution, the mixture turned to a yellow orange color. The effect of

decreased HCl concentration on the equilibrium was the generation of more of it. The equilibrium will shift backward in a reaction producing more HCl molecules. When Na2CrO4 solution was added with 6M NH4OH, the solution’s color turned yellow orange. This means that equilibrium rate of forward and backward reactions were met. Table 1 shows the data and results in the application of the law of chemical equilibrium to solubility equilibrium. Only Na2C2O4 was immiscible and did not mix with BaCl2. Knowing the concepts of chemical equilibrium, one may know how different factors like temperature, solubility and concentration may affect the reactants in an equilibrium reaction. Hence, in experimentations they would tend to be conscious and well-oriented of the different dynamics that may affect adversely the results of their experiments.

REFERENCES Books Balasta, M.L.F., et al. Laboratory Manual and Workbook for General Chemistry. Part Two. Manila: Integrated Research Center, DLSU, 1983. Brown, T.L., H. Eugene le May, Jr., and Bruce E. Bursten. Chemistry: The Central Science. 7th Edition. New Jersey: Prentice-Hall International, 1997. Chang, R. General Chemistry The Essential Concepts 5th Edition. 2008. McGraw-Hill. Singapore Samonte, J.L. & Figueroa L.V. General Chemistry Laboratory Manual 3rd Edition. 2007. C & E Publishing Inc. Quezon City. Philippines.