LE CHATELIER AND EGGSHELLS

Chickens do not perspire and so (like dogs) pant to cool themselves. Panting has been found to cause chickens to lay eggs with thin shells. This surprising result can be explained using Le Chateller's principle and the following equilibria:

CO_2(g) + H₂O_(l)       H₂CO_3(aq)        2H⁺_(aq) + CO₃^2-_(aq)

CO₃^2-_(aq) + Ca²⁺_(aq)       CaCO_3(s)

When a chicken pants, more CO₂ is expelled from its body than when it breathes normally. The CO₂ is in equilibrium with H₂CO₃ and CO₃^2- in the body. Thus, when more CO₂ is expelled, the equilibrium in the first reaction above shifts to the left. This lowers the equilibrium concentration of CO₃^2- in the chicken's body. The CO₃^2- is required to form CaCO₃, a major component of eggshells. Thus, according to the second reaction, the lower concentration of CO₃^2- leads to less CaCO₃ and thin eggshells. One solution to the problem is to give chickens carbonated water to drink in hot weather. The CO₂ dissolved in the water adds CO₂ to the body fluids of the chickens and shifts the equilibria the right.