Consider the following equilibrium:
PCl3 (g) + Cl2 (g) yields PCl5 (g)
delta H= -92KJ
The concentration of PCl3 at equilibrium may be increased by:
decreasing the temp (think this is it)
adding Cl2 to the system
the addition of neon
the additio of PCl4
I don't think so. Remember that Le Chstelier's Principle says that when a system in equilibrium is disturbed it will shift so as to undo what we've done to it.
When dH is involved I rewrite the equation to make more sense.
PCl3 + Cl2 ==> PCl5 + heat
Now, adding PCl3 makes the system want to use up the added PCl3. How can it do that? By reacting more PCl3 with Cl2 to produce PCl6; i.e., shifting the rxn to the right.
Adding more cl2 will shift to the right.
Adding PCl5 will shift to the left.
Adding heat will make it shift to the left.
Sir, thank you for answering. I thought it was the adding the Cl2, but it was wrong. That is why I went with decreasing the temp, but now knowing that it is wrong as well. I think my only option is the addition of PCl5 (which I meant to put at the top vice Pcl4) I hope I am on the right track.
Adding heat and adding PCl5 is th only way to shift it to the left (or course decreasing PCl3 and Cl2 will shift it to the left also). Decreasing T shifts the reaction to the right (because if we take temperature away the reaction will shift to the right in order to produce more heat).
To determine how the concentration of PCl3 at equilibrium can be increased, we can refer to Le Chatelier's principle. Le Chatelier's principle states that when a system at equilibrium is subjected to a change, it will shift in a way that counteracts the change and restores equilibrium.
In this case, the given equilibrium reaction is:
PCl3 (g) + Cl2 (g) ⇌ PCl5 (g)
According to Le Chatelier's principle, increasing the concentration of any of the reactants will shift the equilibrium to the right to consume the additional reactant. Conversely, decreasing the concentration of any of the reactants will shift the equilibrium to the left to produce more of that reactant.
Based on this information, we can evaluate the options:
1. Decreasing the temperature: This is the correct choice. According to the given negative delta H value (-92 KJ), the forward reaction is exothermic. By decreasing the temperature, we effectively "adding heat" to the system. According to Le Chatelier's principle, the system will shift in the endothermic direction to counteract the decrease in temperature. In this case, the system will shift to the right, increasing the concentration of PCl3.
2. Adding Cl2 to the system: Adding Cl2 will increase the concentration of a reactant. According to Le Chatelier's principle, the reaction will shift to the right to consume the additional Cl2. This will result in the production of more PCl5, but it will not directly affect the concentration of PCl3.
3. The addition of neon: Neon (Ne) is an inert gas that does not participate in the chemical reaction. Adding an inert gas does not affect the equilibrium position. Therefore, it will not directly change the concentration of PCl3.
4. The addition of PCl4: PCl4 is not one of the reactants or products in the given reaction. Adding PCl4 to the system will not affect the equilibrium position or the concentration of PCl3.
In conclusion, to increase the concentration of PCl3 at equilibrium, we should decrease the temperature.