expt 9-chemical equilibrium

Experiment No. 9

Chemical Equilibrium

Group 3:Athena Paula BalbinCrystle Cotingting

Objectives:To evaluate and explain the effect

of change in concentration and temperature on the equilibrium

To interpret the result based on the Le Chatelier’s principle

Chemical Equilibrium Chemical Equilibrium is a state of

dynamic 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 Chatelier’s Principle“If 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

Three (3) Factors that can disturb a chemical equilibrium:

1.Change in reactant or product concentrations

2.Change in the pressure

3.Change in temperature

The concept of Le Chatelier’s principle is important in determing direction of reaction.

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

Methodology

Color of mixture?

10 drops of 20 drops Fe(NO3)3 +

20 drops KCNS + 10 mL distilled water

Test tube 1

Test tube 2

Test tube 3

Test tube 4

Test tube 5

Test tube 6

Test tube 7

Test tube 8

10 drops distlled water

10 drops Fe(NO3)3

10 drops KCNS

10 drops KCl

10 drops AgNO3

10 drops NaF

Ice bath

Heat over fire

Resulting color of mixture?

reference

Results:reactant/treatment

observations Direction of reaction

Distilled water

0.1 M Fe(NO3)3 Darker forward

0.1 M KCNS darker forward

0.1 M KCl Lighter backward

0.1 M AgNO3 Milky white backward

NaF crystals Milky white backward

Increase in temp. Lighter Backward

Decrease in temp.

Darker Forward

20 drops Fe(NO3)3 + 20 drops KCNS +

10 mL distilled water

10 drops NaF10 drops AgNO310 drops KCl10 drops KCNS10 drops Fe(NO3)3

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+ + CNS- ↔ FeCNS2+

orange colorless blood-red

Change in the concentration of reactant/product

“If 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

-Although 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.

Effect of temperature changes• Equilibrium constant changes with changes in temperature.

• Treat heat, ∆H, as if it were a chemical reagent

•Endothermic: Reactants + ∆H ↔ product

•Exothermic: Reactants ↔ 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

•Increase in temperature results in shift is to the left

•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 Chatelier’s 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 Chatelier’s Principle.

According to Le Chatelier’s 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.