Le Chateliers WKS KEY - Dr. F PDF

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Le Chatelier's Principle Worksheet KEY 1. Balance the equilibrium reaction shown below and predict whether the equilibrium will shift towards products or reactants under the changing conditions below. 2 NaHCO3 (s) + heat

↔

Na2CO3 (s) +

CO2 (g) +

H2O (g)

the temperature is lowered: Reactants reaction is endothermic in forward direction, lower T favors reactants. H2O condenses on the upper walls of the flask Products condensing the water is the same as removing the gaseous water from the flask CO2 is allowed to escape from the reaction vessel: Products removal of a product causes shift toward product side the size of the reaction vessel is decreased: Reactants pressure increase causes shift to produce less moles of gas NaHCO3(s) is added: NO EFFECT the concentration of a solid is constant and its value is already part of the experimental Kc value Na2CO3(s) is added: NO EFFECT 2. Balance the equilibrium reaction shown below and predict whether the equilibrium will shift towards products or reactants under the changing conditions below. 2 C6H6 (l) +

15 O2 (g)

↔

12 CO2(g) +

6 H2O (g) + heat

O2 is removed from the reaction vessel: Reactants removal of a reactant causes shift to reactant side CO2 is added to the reaction vessel: Reactants addition of a product causes shift to reactant side the size of the reaction vessel is decreased: Reactants smaller volume = higher pressure; system shifts to produce fewer gas particles some Ar(g) is added to the vessel : NO EFFECT addition of an inert gas does not change partial pressure of reaction gases so no change. the temperature is increased: Reactants the reaction is exothermic. Adding heat will shift the reaction away from the “heat” product. 3. Balance the equilibrium reaction shown below and predict whether the equilibrium will shift towards products or reactants under the changing conditions below. N2O4(g) ↔ 2 NO2 (g) the size of the reaction vessel is decreased: a decrease in pressure causes a shift to produce more moles of gas the temperature is increased: an N-N bond must be broken in this reaction – endothermic in forward direction NO2 is removed from the flask: some N2 is added to the flask: (Inert Gas)

Reactants Products Products NO EFFECT

4. Balance the equilibrium reaction shown below and predict whether the equilibrium will shift towards products or reactants under the changing conditions below. 4 SO3(g) +

N2

↔

4 SO2 (g) +

the volume of the vessel is increased: the temperature is increased: reaction has a positive ∆H – endothermic SO2 is removed from the flask: some S8(s) is added to the flask: elemental sulfur is not part of the equilibrium system

2 NO (g)

∆H = 536 kJ Products Products Products NO EFFECT

5. Consider the equilibrium process shown below for the dissociation of acetic acid, a weak acid (weak electrolyte). Predict whether the equilibrium will shift towards products or reactants under the changing conditions below. CH3CO2H(aq)

↔

CH3CO2– (aq)

+

H+ (aq)

acetic acid (CH3CO2H(l)) is added to the flask Products acetic acid is soluble in water and will dissolve to increase the concentration of aqueous acetic acid. sodium acetate (NaCH3CO2(s)) is added to the flask Reactants sodium salts are soluble; aqueous acetate ion is produced hydrochloric acid (HCl(aq)) is added to the flask Reactants HCl is a strong acid in water and dissociates to give H+ and Cl– ions sodium hydroxide (NaOH(aq)) is added to the flask Products + + – → removes H : H + OH H 2O 6. Consider the equilibrium process shown below for the reaction of ammonia with water. Ammonia is a weak base Predict whether the equilibrium will shift towards products or reactants under the changing conditions below. NH3(aq) + H3O(l) ↔ NH4+(aq) + OH–(aq) ammonia (NH3(g), very soluble) is added to the flask sodium hydroxide (NaOH(s)) is added to the flask hydrochloric acid (HCl(aq)) is added to the flask removesOH– : H+ + OH– → H2O ammonium chloride (NH4Cl(s)) is added to the flask ammonium salts are soluble, NH4+is produced

Products Reactants Products Reactants

7. Consider the equilibrium process below involving the dissolution of silver chloride, a semi-soluble salt. Predict whether the equilibrium will shift towards products or reactants under the changing conditions below. AgCl(s)

↔

Ag+ (aq) + Cl– (aq)

the temperature is increased: AgCl(s) is added to the flask: Solids have a constant concentration AgNO3(s) is added to the flask: Nitrate salts are soluble; adds Ag+to solution. CuCl2(s) is added to the flask: CuCl2 dissolves to produce Cl– in solution Ag(s) is added to the flask: Cu(s) is added to the flask: Cu(s) reacts with Ag+ ions to make Ag(s) removing the ions from solution

Products NO EFFECT Reactants Reactants NO EFFECT Products

8. Consider the process below involving the vapor pressure equilibrium between water and water vapor in a sealed container (like a drink bottle). Predict whether the equilibrium will shift to favor products or reactants under the changing conditions below. H2O(l) ↔ H2O(g) liquid water is added to the flask (hint: does it change the concentration?)

NO EFFECT

water vapor is added to the flask

Reactants

the temperature is lowered

Reactants

the volume of space above the liquid is increased

Products

nitrogen gas is added to the space above the flask

NO EFFECT...