What effect do the following changes have on the position of equilibrium (which way does the equilibrium shift) for the reversible endothermic reaction? PCL5+ heat <-> PCL3(g)+ CL2(g)
A) removal of PCL3, as it is formed
B)addition of CL2
C) decrease in pressure
D) putting in an ice bath
A) removal of PCl3, as it is formed:
Equilibrium will shift to the left. Removing PCl3 is like taking away the VIP of the reaction. Without its presence, the equilibrium feels lonely and shifts to the side where PCl3 is produced to find some company.
B) addition of Cl2:
Equilibrium will shift to the right. Adding Cl2 is like adding a pinch of spice to the recipe. The reaction will shift towards the side where Cl2 is consumed to balance out the added ingredient.
C) decrease in pressure:
Equilibrium will shift to the side with more moles of gas. In this case, since there are two moles of gas on the reactant side (PCl5) and only one mole of gas on the product side (PCl3 + Cl2), the reaction will shift to the left to decrease the pressure and create more reactants.
D) putting in an ice bath:
Equilibrium will shift to the right. When you put the reaction in an ice bath, it gets chilly and reacts by moving towards the side with more heat (the right side). So, the reaction will shift to the right to warm things up a bit.
Remember, these are just jokes! In reality, the equilibrium shift can be determined by Le Chatelier's principle and the reaction's enthalpy, pressure, and moles of gas.
A) Removal of PCL3, as it is formed:
The removal of PCL3 would shift the equilibrium towards the products side to replace the PCL3 that was removed. According to Le Chatelier's principle, the system will try to counteract the removal of PCL3 by producing more of it.
B) Addition of CL2:
The addition of CL2 would shift the equilibrium towards the reactants side. This is because CL2 is on the product side of the reaction and by adding more of it, the system will try to counteract the increase by favoring the reactants.
C) Decrease in pressure:
A decrease in pressure would favor the side of the reaction with a higher number of moles of gas. In this case, the reactants side has 1 mole of gas (PCL5) while the products side has 2 moles of gas (PCL3 and CL2). Therefore, a decrease in pressure would shift the equilibrium towards the products side to balance out the decrease in pressure.
D) Putting in an ice bath:
Putting the reaction in an ice bath would decrease the temperature. Since the reaction is endothermic, it absorbs heat. By decreasing the temperature, the system will try to compensate for the decrease in heat by shifting the equilibrium towards the exothermic side. In this case, it would shift towards the reactants side to generate more heat.
To determine the effect of these changes on the position of equilibrium, we need to consider Le Chatelier's principle. According to the principle, if a system at equilibrium experiences a change, it will shift in a way that minimizes the effect of that change.
A) Removal of PCl3: If PCl3 is removed from the system, the equilibrium will shift to the right to produce more PCl3. This is known as the "common-ion effect." By removing PCl3, the equilibrium is disturbed, and the system tries to counteract the change by producing more PCl3.
B) Addition of Cl2: The addition of Cl2 to the system will also shift the equilibrium to the right. This is because increasing the concentration of Cl2 will cause the reaction to produce more PCl3 and reach a new equilibrium.
C) Decrease in pressure: Decreasing the pressure will shift the equilibrium to the side with more moles of gas. In this case, PCl3 is a gas while PCl5 and Cl2 are both in the liquid or solid state. Since there are fewer moles of gas on the right side of the equation, decreasing the pressure will shift the equilibrium to the right to increase the gas molecules and establish a new equilibrium.
D) Putting in an ice bath (lowering the temperature): Since the reaction is endothermic (heat is a reactant), putting the system in an ice bath will decrease the temperature. According to Le Chatelier's principle, when the temperature is decreased, the equilibrium will shift to the side of the reaction that produces heat. In this case, it will shift to the right to produce more PCl3 and Cl2, which are both exothermic products.
In summary:
A) Removal of PCl3 shifts the equilibrium to the right.
B) Addition of Cl2 shifts the equilibrium to the right.
C) Decrease in pressure shifts the equilibrium to the right.
D) Putting in an ice bath shifts the equilibrium to the right.
PCl5(g) + heat <-> PCl3(g)+ Cl2(g)
A) removal of PCl3, as it is formed
B)addition of Cl2
C) decrease in pressure
D) putting in an ice bath
What does Le Chatelier's Principle say. In long words it is this.
When a chemical system in equilibrium is subjected to a stress it will shift in such a way so as to relieve the stress. My students never got that so we came up with a simpler one. Here it is. A system in equilibrium will try to undo what we do to it.
For A. If we remove PCl3 the system will shift to form more of it. Simple. Shifts to the right; therefore, the amount of Cl2 @ equilibrium will be higher and the amount of PCl5 will be smaller.
C. If we decrease pressure the system will shift to lessen the pressure. How can it do that? By decreasing the number of moles of gas. So it will shift to the left BECAUSE there are fewer moles on the left (1 mol gas) than the right(2 mols gas). So the amount of PCl3 and Cl2 will decrease at equilibrium because there are fewer moles of gas present that way.
I've never understood why students get confused over this. In my opinion it is the simplest fundamental principle in chemistry. I'll leave B and D for you to do. I shall be happy to check your answers.