Blog 9.2 LeChatlier's Principle (Due April 17th)

Blog 9.2: LeChatelier's Principle

Station One

 Explain the shift that happened when HCl was added.

 1.    Explain the shift that happened when the system was heated, based on the location (products side or reactants side) of “heat energy” in the reaction.

2.   Describe how the Delta H (heat of reaction) shows whether the reaction is endothermic or exothermic. Relate this to potential energy and also the + or - sign of delta H.

 3.    

a. What does Table F say about the interaction between Ag¹⁺ ion and Cl^1- ion?

b. From your observations about what happened when you added AgNO₃, what evidence do you have that the Table F interaction happened?

c. Explain the shift caused by adding AgNO₃.

Station Three Processing Question:

6.  In terms of pressure changes, explain how your observations help to make sense of the fact that a carbonated beverage begins to effervesce (release gas) as soon as the bottle is opened.  (A chemist might say the reaction “shifts to the right” as soon as the container is opened!)

ENRICHMENT: 

Chickens Lose Equilibrium…Problem Solved Applying Le Chatelier

By David B. Brown & John A. MacKay III

Chickens cannot perspire, so when they get hot, they pant.  This seemingly trivial fact led to a serious economic loss for egg producers.  In hot weather, chickens lay eggs with thin shells that are easily (and frequently) broken.  A little reflection shows that this is an inevitable consequence of Le Chatelier’s principle and the well-known carbon dioxide equilibrium system.

CO₂ (g)  <-->  CO₂ (aq) <--> H₂CO₃(aq) <--> H⁺ + (CO₃)^2-(aq) <--> CaCO₃(s)

(chicken breath) ------------- (chicken metabolism) ---------------------- (egg shell)           

When the chicken pants, the equilibrium is perturbed by the rapid loss of carbon dioxide.  Because this effect cascades through all of these equilibria, the effect is a loss of solid calcium carbonate, which ultimately produces weaker egg shells.

Ted Odom, while a graduate student at the University of Illinois, found the deceptively simple “solution” to this problem – give the chickens carbonated water.  Now the equilibrium has been perturbed in the opposite direction.  The addition of aqueous carbon dioxide shifts all of the equilibria to the right and results in stronger egg shells.  Moreover, the chickens seem to like the carbonated water, and there are rumors that they spend their spare time singing familiar singles about “spirit” and the “real thing.”  Philosophical questions about which came first are left to the reader, but in this case, at least, Le Chatelier’s principle comes before the egg (shell).

Questions:

1.)    What gas do chickens pant out?

2.)    When the [CO₂] decreases, which way does the equilibrium shift?

3.)    When the equilibrium shifts, what happens to the amount of the CaCO₃(s) (the egg shell) that is produced?

4.)    Explain why panting results in thinner egg shells.

5.)    What change could farmers make to assure thicker egg shells in hot weather?  How does this change take advantage of Le Chatelier’s principle?