Le Chatelier's Principle
Silver Chloride Equilibrium. Chloride ion precipitates silver ion as AgCl. Addition of chloride ion (from HCl) to the above solution containing Ag+ causes the formation of a silver chloride, AgCl, precipitate, now in dynamic equilibrium with its Ag+ and Cl- ions
Aqueous ammonia, NH3, "ties up" (i.e., it forms a complex ion with) silver ion, producing the soluble diamminesilver(I) ion, [Ag(NH3)2]+. The addition of NH3 removes silver ion from the equilibrium in equation 16.9, shifting its equilibrium posi- tion to the left and causing AgCl to dissolve. Adding acid, H+, to the solution again frees silver ion to recombine with chloride ion and re-forms solid silver chloride. This occurs because H+ reacts with the NH3 (see equa- tion 16.4) in equation 16.10, restoring the presence of free Ag+ to combine with the free Cl- to form AgCl(s) shown in equation
The colors of the solutions change, however, in the presence of added ammonia, NH3
Because the metal-ammonia bond is stronger than the metal-water bond, ammonia substitution occurs and the following equilibria shift RIGHT, forming the metal-ammonia complex ions:
When are the rates of the forward and reverse reaction unequal.
Before equilibrium is established
increase the rate of rxn by decreasing its activation energy, has no effect on equilibrium concentrations.
Catalyst
How is "bumping" avoided in the preparation of a hot water bath?
Caution must be taken not to heat the liquid too rapidly as "bumping" (the sudden formation of bubbles from the superheated liquid) may occur. To avoid or to minimize bumping, place a stirring rod followed by constant stirring or boiling chips into the liquid. If a stirring hot plate is used, place the stir bar into the liquid and turn on the stirrer
The rate of the forward reaction is equal to the rate of the reverse reaction
Chemical Equilibrium
occurs when the rate of the forward rxn is equal to the rate of the reverse rxn
Chemical Equlibrium
an explanation of the variability in reaction rates that is based on the idea that molecules must collide in order to react
Collision Theory
The addition of OH- shifts the buffer equilibrium, according to LeChâtelier's principle, to the right because of its reaction with H3O+, forming H2O.The shift right is by an amount that is essentially equal to the moles of OH- added to the buffer system. Thus, the amount of CH CO - increases, and the amount of CH COOH decreases by 323 an amount equal to the moles of OH- added:
Conversely, the addition of H3O+ from a strong acid to the buffer system causes the equilibrium to shift left, the H3O+ combines with the acetate ion (a base) to form more acetic acid, an amount (moles) equal to the amount of H3O+ added to the system. As a consequence of the addition of strong acid, the amount of CH3COOH increases, and the amount of CH CO - decreases by an amount equal to the moles of 32 strong acid added to the buffer system. This experiment compares the pH changes of a buffered solution to those of an unbuffered solution when varying amounts of strong acid or base are added to each
This experiment examines the effect of temperature on the system described by equation 16.17 4 Cl-(aq) + [Co(H2O)6]2+(aq)<-----> [CoCl4]2-(aq) + 6 H2O(l) This system involves an equilibrium between the coordination spheres, the water versus the Cl- about the cobalt(II) ion; the equilibrium is concentration and temperature dependent. The tetrachlorocobaltate(II) ion, [CoCl4]2-, is more stable at higher temperatures.
Coordination sphere: all ligands of the complex ion (collectively with the metal ion they are enclosed in square brackets when writing the formula of the complex ion).
A state of dynamic equilibrium, Ag CO (s) 2Ag+(aq) + CO 2-(aq), exists in solution. *d. What shift occurs in the equilibrium if HCl(aq) is added to the system? Explain.
Equilibrium will shift to the right if HCl is added to the system because the Ag+ions produced will be consumed in precipitate formation as AgCl with HCl. Also H+ will remove CO3^2- as (H2O) and CO2) and this also has the effect of shifting the equilibrium to the right.
What happens to the equilibrium if a reactant's concentration is decreased?
Favors the reverse reaction
For the rxn A + B <−> C + D, what happens if C or D are reduced?
Forward rxn is favored
A state of dynamic equilibrium, Ag CO (s) 2Ag+(aq) + CO 2-(aq), exists in solution. What shift, if any, occurs in the equilibrium if AgNO3(aq) is added to the system?
If Ag2NO3 is added to the system in the equilibrium, then this will increase the ions. The reactions will shift to the left side as reaction wants to compensate this addition
general statement governing all systems in a state of dynamic equilibrium This is LeChâtelier's principle, proposed by Henri Louis LeChâtelier in 1888.
If an external stress (change in concentration, temperature, etc.) is applied to a system in a state of dynamic equilibrium, the equilibrium shifts in the direction that minimizes the effect of that stress.
CO₂(aq) ↔ CO₂ (g) ∆H = +KJ (endo) Use Le Chatelier's principle to explain why is it important to serve "fizzy" drinks chilled rather than warm?
If fizzy drink gets warm the system will oppose the change by moving in the enothermic direction. Less CO₂is dissolved and drink will go flat.
states that changing a factor such as concentration, temperature, or pressure of a rxn at equilibrium will cause the reaction to shift in the direction that counteracts the effect of that change
Le Chatelier's Principle
State whether a high or low temperature and a high or low pressure should be used to maximize the yield of product: 2SO₂(g) + O₂(g) ↔ 2SO₃(g), ∆H = -kJ (exo)
Low temperature (Opposes decrease by moving in exdothermic direction) High pressure (Opposes increase by moving to side with least moles)
Consider the following exothermic reaction in equilibrium: 4HCl(g) + O₂(g) ↔ 2Cl₂(g) + 2H₂O(g) State, with a reason, what would happen to the amounts of chlorine and hydrogen chloride if a catalyst is introduced.
NO CHANGE in [HCl] or [Cl] as a catalyst speeds up the rate of both the forward and backward reaction.
Silver Carbonate Equilibrium. The first of the silver salt equilibria observed in this experiment is that of a saturated solution of silver carbonate, Ag2CO3, in dynamic equilibrium with its silver and carbonate ions in solution.
Nitric acid, HNO3, dissolves silver carbonate: H+ ions react with (and remove) the CO 2- ions on the right; the system, in trying to replace the CO 2- ions, shifts to 33 the RIGHT. The Ag2CO3 dissolves, and carbonic acid, H2CO3, forms.The carbonic acid, being unstable at room temperature and pressure, decomposes to water and carbon dioxide. The silver ion and nitrate ion (from HNO3) remain in solution.
A state of dynamic equilibrium, Ag CO (s) 2Ag+(aq) + CO 2-(aq), exists in solution. a. What shift, if any, occurs in the equilibrium if more Ag2CO3(s) is added to the system?
Since Ag2CO3 is a solid the equilibrium is not shifted
Q. The Haber process involves an equilibrium reaction: N₂(g) + 3H₂(g) ↔2NH₃(g), ∆H = -kJ The reaction is carried out at 450 ° C and 250 kPa with an iron catalyst. Give two reasons why a lower pressure is not used
System would oppose change move backwards in favor of more moles and yield of NH₃ would decrease. Collision frequency would decrease so rate decreases.
Consider the following exothermic reaction in equilibrium: 4HCl(g) + O₂(g) ↔ 2Cl₂(g) + 2H₂O(g) State, with a reason, what would happen to the amounts of chlorine and hydrogen chloride if the temperature of the container was increased.
The [HCl] ↑ and [Cl]↓ as system moves to left to oppose increase in temperature and moves in endothermic direction.
Consider the following exothermic reaction in equilibrium: 4HCl(g) + O₂(g) ↔ 2Cl₂(g) + 2H₂O(g) State, with a reason, what would happen to the amounts of chlorine and hydrogen chloride if water is removed.
The [HCl] ↓ and [Cl]↑ as system moves to right to oppose removal of water
Addition of strong acid, H+, affects these equilibria by its reaction with ammonia (a base) on the left side of the equations:
The ammonia being removed from the equilibria causes the reactions to shift LEFT to relieve the stress caused by the removal of the ammonia, re-forming the aqueous Cu2+ (sky blue) and Ni2+ (green) solutions. For copper ions, this equilibrium shift may be represented as
dynamic equilibrium
The apparent cessation of the reaction before a 100% yield is to obtained implies that the chemical system has reached a state where the reactants combine to form the products at a rate equal to that of the products re-forming the reactnants
Define dynamic equilibrium
When the rate of the forward reaction is equal to the rate of the reverse reaction and concentrations of reactants and products remain unchanged.
Describe the dynamic equilibrium that exists between the two water tanks at right
When two tanks are connected by a pipe- any difference in amount of water in any tank is immediately balanced by appropriate change in the other tank
Explain how LeChâtelier's principle applies when water is added to the right tank.
When water is added to the right tank, the amount of water in the tank increases. to counter this, some water flows to the left tank, establishing equilibrium
Ligand:
a Lewis base that donates a lone pair of electrons to a metal ion, generally a transition metal ion
an aqueous solution that resists a pH change when small amounts of acid or base are added
a buffered medium/ buffer A buffer solution must be able to consume small additions of H3O+ and OH- with- out undergoing large pH changes. Therefore, it must have present a basic component that can react with added H3O+ and an acidic component that can react with added OH-. Such a buffer solution consists of a weak acid and its conjugate base (or weak base and its conjugate acid). This experiment shows that the ACETIC ACID ACETATE buffer system can minimize large pH changes:
Two factors affecting equilibrium position are studied in this experiment:
changes in concentration and changes in temperature.
The effect of adding an ion or ions common to those already present in a system at a state of dynamic equilibrium is called the
common-ion effect. The effect is observed in this experiment for the following equilibrium: 4 Cl-(aq) + [Co(H2O)6]2+(aq) <--> [CoCl4]2-(aq) + 6 H2O(l)
When the forward and reverse reaction occur at the same rate, the reaction is said to be in ___________
equilibrium
What happens to the smog levels with Increasing temperatures
Smog levels rise.
Q. The Haber process involves an equilibrium reaction: N₂(g) + 3H₂(g) ↔2NH₃(g), ∆H = -kJ The reaction is carried out at 450 ° C and 250 kPa with an iron catalyst. Give one reason why a higher temperature is not used.
System would oppose change move backwards in endothermic direction and yield of NH₃ would decrease.
What happens to the equilibrium of an endothermic rxn if heat is added?
The forward rxn is favored because heat is a reactant.
How does the equilibrium change if a catalyst is added?
No change in equilibrium (catalysts only change rate at which equilibrium is reached)
c. After water is added to the system and equilibrium is reestablished: (i) what change in the number of moles of Ag+(aq) occurs in the system? Explain. (ii) what change in the concentration of Ag+(aq) occurs in the system? Explain.
(i)water is used as solvent and in water, Ag2CO3 will dissolve maximum and reestablish equilibrium.Meaning the moles of AG+ is the same in both backwards and forward direction (ii)When one changes the concentration of ions in the solution that belongs to an equilibrium occurring in solution, the effect on equilibrium occurring in solution, the effect on equilibrium is called the common ion effect
Reactants turn into products and products turn into reactants
A reversible reaction.
The following chemical equilibria are studied in this experiment. To become familiar with their behavior, indicate the direction, left or right, of the equilibrium shift when the accompanying stress is applied to the system. a) NH3(aq) is added to Ag+(aq) + Cl-(aq) <---> AgCl(s) b) HNO (aq) is added to Ag2CO3(s) <---> Ag+(aq) + CO3^2- (aq) c) KI(aq) is added to Ag+(aq) + 2 NH3(aq) <--->[Ag(NH3)2]+(aq) d) Na2S(aq) is added to AgI(s) <--->Ag+(aq) + I-(aq) e) KOH(aq) is added to CH3 COOH(aq) + H 2O(l) <--->.H3O+(aq) +CH3CO2 - (aq) f) HCl(aq) is added to 4 Cl-(aq) + Co(H2 O)6^ 2+ (aq) CoCl4^ 2- (aq) + 6 H2 O(l)
A)Left B)Right C)Left D)Right E)Right F)Right
Note the dynamic equilibrium in the opening photo. Which solution changes color when the pH of both solutions is increased?
Shift equilibrium to the right convert yellow to orange if already orange will not do anything
Is equilibrium static or dynamic?
Dynamic: the reaction keeps going in the forward and reverse directions
What happens to the equilibrium if a reactant's concentration is increased?
Favors the forward reaction
Silver Iodide Equilibrium. Iodide ion, I- (from KI), added to the Ag+(aq) + 2 NH3(aq)<---->Ag(NH ) +(aq) equilibrium in equation 16.10 results in the formation of solid 32 silver iodide, AgI.
The iodide ion removes the silver ion, causing a dissociation of the [Ag(NH3)2]+ ion and a shift of the equilibrium to the LEFT
Define position of equilibrium
The ratio of the concentration of products to reactants
2 NO2(g)<---->N2O4(g) + 58 kJ
The reaction for the formation of colorless N2O4 is exothermic by 58 kJ. To favor the formation of N2O4, the reaction vessel should be kept cool (Figure 16.4 right); removing heat from the system causes the equilibrium to replace the removed heat and the equilibrium therefore shifts RIGHT. Exothermic: characterized by energy release from the system to the surroundings
What happens to the equilibrium of an exothermic rxn if heat is added? Why?
The reverse rxn is favored because heat is a product.
For the rxn: 2A (g) + 3B (g) <−> C (g) + 3D, what happens if pressure is reduced?
The reverse rxn is favored because the equilibrium shifts toward the larger moles of gas which are on the left side.
CO₂(aq) ↔ CO₂ (g) ∆H = -kJ (exo) Use Le Chatelier's principle to explain what happens to the CO₂ concentration in water when a can of soft drink is shaken up and then opened.
The system is no longer just the bottle but the universe. The [CO₂] in the universe is much lower so the system will move to the right to oppose the change. Dissolved CO₂decreases and so the drink goes 'flat'.
Q. The Haber process involves an equilibrium reaction: N₂(g) + 3H₂(g) ↔2NH₃(g), ∆H = -kJ The reaction is carried out at 450 ° C and 250 kPa with an iron catalyst. Why is a catalyst used?
To lower the actiavtion energy and speed up the reaction.
Explain how LeChâtelier's principle applies when the faucet on the right tank is opened
When the faucet on the right tank is opened, the amount of water in the right tank decreases. To counter this change water flows in from the left tank so the equilibrium is established once again
When is equilibrium established?
When the rate of the forward and reverse reaction are equal. There is no overall change in concentration.
Define Le Chatelier's principle
any change in a system at equilibrium results in a shift of equilibrium in direction which minimizes (opposes) change. "dynamic equilibrium concept"
Will the addition of NaC2H3O2 to a CH3COOH solution cause the pH to increase or decrease?
as salt increase log(salt/acid) value also increases, resulting PH will increase
Le Chatelier's principle states that
if a system at equilibrium is disturbed, the equilibrium position will shift to counter the effects of the disturbance
When you take something away from a system at equilibrium the system shifts in such a way as to _________ some of what you've taken away
replace
4 Cl-(aq) + [Co(H2O)6]2+(aq) <--> [CoCl4]2-(aq) + 6 H2O(l)
represents an equilibrium of the ligands Cl- and H2O bonded to the cobalt(II) ion—the equilibrium is shifted because of a change in the concentrations of the chloride ion and water.
endothermic: decreasing temperature causes __________
shift left (reverse)
exothermic: increasing temperature causes ________
shift left (reverse)
increasing concentration of products causes_________
shift left (reverse)
endothermic: increasing temperature causes __________
shift right (forward)
exothermic: decreasing temperature causes __________
shift right (forward)
increasing concentration of reactants causes___________
shift right (forward)
increasing volume causes __________
shift towards greater moles of gas particles
decreasing volume causes __________
shifts towards fewer moles of gas particles
Aqueous solutions of copper ions and nickel ions appear:
sky blue and green, respectively
Experimental Procedure. Cite the reason for each of the five cautions in the experiment.
strong odor do not inhale avoid breathing vapors and avoid skin contact Avoid inhalation and skin contact
When you add something to a sys at equilibrium the system shifts in such way as to _______ some of what you've added
use up
