Help with Le Chatlier's Principle question?? Please HELP?????? GENCHEM2

Question

Hi everyone, I am really stuck on this problem, and I don't really think I understand Le Chatlier's principle very well. However, I would like to learn for sure!! Thank you for the help!!!

 

For each of the following reactions, determine which direction the equilibrium will shift for the given conditions (to the right, to the left, or no shift). Explain your reasoning.
5. P4(s) + 5O2(g) ↔ P4O10(g)  delta H =- 
a. The total pressure is decreased

 

b. Some oxygen is removed

 

c. The temperature is decreased

Answer 1

Hi Angelica

 

Le Chatelier's principle gives you a qualitative picture of what happens to the equilibrium position when a change is imposed on a system. The shift in the position occurs in the direction that reduces the change. Changes that affect the position of an equilibrium system range from changing the concentrations of reactants or products and changing the pressure or the temperature of the system.

 

a) There are three ways that you can change the pressure of an equilibrium system.

- You can add or remove a gaseous reactant or product

- You can add an inert gas that is not part of the system. Note that the addition of an inert gas does affect the total pressure of the system but not the partial pressures or concentrations of the individual components of the system. Thus in this case no shift occurs.

- You can change the volume of the system. At constant P and T, the volume of the system is directly proportional to the number of moles of the individual components so the shift will occur depending on how the volume changes.

 

In this case the volume of the system is increased which decreases the total pressure (P and V have an inverse relationship; try to see why from the ideal gas law). Since volume is directly proportional to the number of moles of the individual components, the system will shift in the direction where there are more molecules. In this case the shift is to the right (there are five molecules of oxygen).

 

b) In this case you are dealing with concentration changes. By removing oxygen the concentration of oxygen decreases so the equilibrium will shift to the left.

 

c) The reaction is exothermic. To see what happens when you decrease the temperature you can treat the energy as a product as follows

 

P₄ (s) + 5O₂ (g)  <-> P₄O₁₀ (g) + KJ

 

Since the reaction is exothermic, a decrease in the temperature will cause the system to shift to the right.

 

Hope this answers your question.