Explain LeChatelier\'s Principle. One of the reactions that is often studied in

Question

Explain LeChatelier's Principle. One of the reactions that is often studied in an equilibrium experiment is NH_3(aq) + H_2O(l) doubleheadarrow NH_4^+ (aq) + OH^- (aq). a. Write the equilibrium constant expression (Law of Mass Action) for this equation. b. Based on your knowledge of LeChatlier's Principle, predict what would happen to the equilibrium if the following changes were made. Explain your reasoning in each case. Be sure to include any secondary reaction involving a common ion if applicable. i. NH_4CI was added to the solution at equilibrium ii. NaOH was added to the solution at equilibrium iii. HNO_3 was added to the solution at equilibrium

Explanation / Answer

Q1.

First, let us state the Le Chatelier principle which deals with changes in an equilibrium:

The statement is as follows:

If any equilibrium is disturbed, that is, change in conditions such as P,T, concentration, partial pressure, etc.., the system will counterbalance such change in order to favour the system's equilbirium.

Q2.

a)

K = [NH4+][OH-]/[NH3]

liquids are not included, since they have activity = 1, so ignore H2O

b)

i) if we ad NH4Cl = NH4+ + Cl- forms, this increases NH4+ concentration, so more NH3 and H2O will be produced, the shift goes to the left

ii)

addition of NaOH = Na+ + OH-

OH- increases, so the shift goes again towards more NH3 and H3O ( left side)

iii)

HNO3 = H+ and NO3-

H+ is acidic, will react with OH-

OH- decreases, so the products decreases

NH3 and H2O must react to form OH-

the shift goes to the Right

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