Chemical Equilibrium and Le Châteller\'s Principle vot plak 6. Reagents: NH,CI (

Question

Chemical Equilibrium and Le Châteller's Principle vot plak 6. Reagents: NH,CI (), DI water, saturated NH,Cl (aq), 12 M HCI (aq) NH,CI (=NH, * (aq) + Cl- (aq) K. =? KEQ 17.18) Hint: Be sure that the saturated ammonium chloride is saturated (i.e has solid ppt at the bottom of the reagent container). If not add ammonium chloride to your beaker until saturated. a. Add about 0.5 g of ammonium chloride to a small test tube, which is about one-third full with DI water. After adding the solid stir and feel the bottom of the test tube to note any temperature change. Record your observations in your lab book. Is the solution of ammonium chloride exothermic or endothermic? Write the net ionic equation, putting heat as a reactant or product. b. To a second test tube add about 3.0 ml of saturated ammonium chloride. c. To this test tube, add 12 M hydrochloric acid (CAUTION!) drop wise until you see a definite change. Record your observations of this change in your lab book. Is the reaction shifted to right or the left? Reason for shift. Write the net ionic equation. d. Put the resulting test tube into a hot water bath while stirring the mixture. Record your observations. Is the reaction shifted to the right or the left? Reason for shift. Write the net ionic equation. e. Put the test tube in ice water. Record your observations. Is the reaction shifted to the right or the left? Reason for the shift. Write the net ionic equation.

Explanation / Answer

a. Test tube becomes cold.

The ammonium chloride solution is endothermic. NH4Cl(s) + H2O (l) + heat energy<---------> NH4+ (aq) + Cl- (aq)

b & c. The test tube gets heated up.

   HCl molecules upon dissociation gives H+ and Cl- ions hence the concentration of Cl- ions on right hand side increases, so the equilibrium shifts towards left.

NH4Cl(aq) ----------> NH4+ (aq) + Cl-(aq)

HCL (aq)------------> H+ (aq) + Cl- (aq)

________________________

NH4Cl(aq) + HCl (aq)<----------> NH4+(aq) + H+ (aq) + 2Cl-(aq)

d. Since the reaction is exothermic if the temperature is raised the reaction proceeds to left.

Since heat is added to the reactants side (left) equilibrium shifts to right

e. Since the reaction is exothermic the cooling effects shifts the equilibrium to right.

Since the heat is removed from the system ( from products side) equilibrium shifts to product side to produce heat again.

Kc = (NH4+) (Cl-)

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(NH4Cl)

  

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