Expt 9-Chemical Equilibrium

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Chemistry 14.1 - General Chemistry Laboratory I

Text of Expt 9-Chemical Equilibrium

Experiment No. 9

Chemical EquilibriumGroup 3: Athena Paula Balbin Crystle Cotingting

Objectives:y To evaluate and explain the effect ofchange in concentration and temperature on the equilibrium

y To interpret the result based on the LeChateliers principle

Chemical Equilibriumy Chemical Equilibrium is a state ofdynamic balance in which the rate of formation of the products of a reaction from the reactants equals the rate of formation of the reactants from the products. The concentrations of the reactants and products remain constant. A+B C

Le Chateliers PrincipleIf a system at equilibrium is disturbed by a change in temperature, pressure, or the concentration of one of the components, the system will shifts its equilibrium position so as to counteract the effect of the disturbance.

Henry Louis Le Chatelier

y Three (3) Factors that can disturb achemical equilibrium:

1.Change in reactant or productconcentrations

2.Change in the pressure 3.Change in temperature

y The concept of Le Chateliers principle isimportant in determing direction of reaction.

y The concept of chemical equilibrium is usedby many manufacturers and factories and so we recommend further and deeper studies regarding this subject matter in order to increase the efficiency of substances.

MethodologyTest tube 1 Test tube 2 Test tube 3 10 drops of 20 drops Fe(NO3)3 + 20 drops KCNS + 10 mL distilled water Color of mixture? Test tube 6 Test tube 7 Test tube 8 10 drops NaF Heat over fire Ice bath Test tube 4 Test tube 5 10 drops distlled waterreference

10 drops Fe(NO3)3 10 drops KCNS 10 drops KCl 10 drops AgNO3 Resulting color of mixture?

Results:reactant/treatmentDistilled water 0.1 M Fe(NO3)3 0.1 M KCNS 0.1 M KCl 0.1 M AgNO3 NaF crystals Increase in temp. Decrease in temp. Darker darker Lighter Milky white Milky white Lighter Darker forward forward backward backward backward Backward Forward

observations

Direction of reaction

20 drops Fe(NO3)3 + 20 drops KCNS + 10 mL distilled water

10 drops Fe(NO3)3 10 drops KCNS

10 drops KCl

10 drops AgNO3

10 drops NaF

Ice bath

Heat over fire

Reference

Discussion:An equilibrium is achieved when 20 drops of 1M Fe(NO3)3, 20 drops of 1M KCNS and water were mixed. The reaction is: Fe3+ + CNSorange FeCNS2+

colorless blood-red

Change in the concentration of reactant/productIf a chemical system is at equilibrium and we add a substance (either reactant/product), the reaction will shift so as to reestablish equilibrium by consuming part of the added substance. Conversely, removing a substance will cause the reaction to move in the direction that forms more of that substance.

Test tube 2 and 3 - basically an increase in concentration of the reactant - to reduce amount of reactant (and reattain equilibrium), shift towards formation of more product (forward direction) - a forward reaction resulted in creation of more FeSCN2+ making solution darker

Test tube 4 - KCl dissociates into K+ and Cl- ions - K+ ions also form a complex with CNS(Fe(CNS)3 + 3KCl FeCl3 + 3KCNS ) - Decrease in amount of reactant CNS- To increase amount of reactant (to reattain equilibrium), the product FeSCN2+ is broken down (reverse shift) - Breakdown of product turns solution lighter - Light brown color can also be attributed to FeCl3 molecules

Test tube 5 -Addition of AgNO3 caused a precipitation of insoluble compound AgCNS Fe(CNS)3 + AgNO3 AgSCN + Fe(NO3)3 -Decrease in the amount of CNS- ions, because also was being used to form AgCNS -To increase amount of reactant (to reattain equilibrium), the product FeSCN2+ is broken down (reverse shift) -Breakdown of product turns solution lighter

Fe(NO3)3, a reactant, was also produced, the effect of the shift towards the breakdown of the FeCNS2+ is more dominant because the AgCNS formed is solid and insoluble.

-Although

Effect of temperature changes Equilibrium constant changes with changes in

temperature. Treat heat, H, as if it were a chemical reagent Endothermic: Reactants + H Exothermic: Reactants product

product + H

When the temperature is increased, it is as if we have added a reactant, or a product, to the system of equilibrium. The equilibrium shifts in the direction that consumes the excess reactant (or product), namely heat.

Endothermic: Like adding more reactants Reduce amount of reactant and reattain equilibrium by shifting towards formation of more products Increase in temperature causes the shift to the right Exothermic: Like adding more products Reduce amount of the product and reattain equilibrium by shifting towards formation of more reactant

Heating test tube 7 resulted in a solution of a lighter color, indicating a shift towards the production of reactants. Placing test tube 8 in an ice bath produced a darker color of solution, indicating a shift towards production of products. Hence, it is an exothermic reaction

Conclusions and Recommendations- Le Chateliers principle has been demonstrated in

this experiment. -An increase in the concentration of the reactant or a decrease in the concentration of the product shifts the direction of the reaction towards the production of more products to return to the equilibrium position. -The opposite, a decrease in the concentration of the reactants or an increase in the concentration of the product shifts the equilibrium position towards the production of more reactants.

-If temperature is treated as a reactant, in an exothermic reaction, an increase in temperature shifts the direction towards the production of more reactants. -A decrease in temperature in an exothermic reaction causes a shift towards the production of products, in order to reestablish equilibrium.

Guide Questions and Answers:1.Explain your observations on the basis of Le Chateliers Principle. According to Le Chateliers Principle if a system is at equilibrium and we add a substance, the reaction will shift so as to reestablish equilibrium by consuming part of the added substance.

If reactants are added or products are removed, the system will reestablish equilibrium by moving in the forward direction and converting the reactants into products. Such is the case in test tubes 2, 3, and 8 (if you treat heat as a reactant). On the other hand, if the concentration of the reactants is decreased, shifting the reaction backwards and decomposing the products into reactants reestablishes equilibrium. Such as demonstrated by test tubes four, five and six and seven (if you treat heat as a reactant).

2.Which species (ions) in the added reagents are effective in altering the state of the system? Fe3+ and CNS- are effective. 3. Is the reaction endothermic or exothermic? Why? The reaction is exothermic, because the reaction shifts backward (a lighter solution was obtained) with an increase in temperature, indicating that the reaction is heat absorbing.