Is the yield of SO₃ at equilibrium favored by a hig...

Question

Is the yield of SO₃ at equilibrium favored by a higher or lower pressure? By a higher or lower temperature?

2 SO₂(g) + O₂ ⇌ 2 SO₃(g) ∆H = -47 kcal/mol

Accepted Answer

Welcome back, everyone which of the following favors the formation of more phosphorus oxy chloride at equilibrium. So we've got the reaction where two moles of phosphorus trichloride gas reacts with one mole of oxygen gas and equilibrium to form two moles of phosphorus oxy chloride gas with an entropy change equal to negative 130 kg per mole. And we have choices A through D which vary as far as having conditions of higher pressure, lower temperature or different variations of the converse. And so we would go ahead and begin by recalling Leat Li's principle. So first, we're going to consider Lelia's principle with regards to changes in pressure on a system in this case, our reaction. And so for a system in equilibrium, specifically, when we have a change in pressure, if we were to, for example, decrease the pressure, recall that according to Lelia's principle, equilibrium is going to shift to the side with more moles of gas. So in this case, we would observe that we've got a total of three moles of gas gaseous reactants on the reactant side and a total of only two moles of gaseous products on the product side. And so we have more moles of gas on the reactant side. So with a decrease in pressure equilibrium will shift to the left and shifting to the left would ultimately create more reactants and lower the concentration of phosphorus oxy chloride gas, our products at equilibrium. So we would therefore want to rather increase the pressure so that equilibrium will shift to the side with less moles of gas. And so that would be the product side because we only have two moles of gas. On the product side, we have two moles of phosphorus oxy chloride gas. And so that would increase the concentration of phosphorus oxy chloride gas if we increase the pressure of our system at equilibrium. So with that understood, we are then going to consider the effect of temperature change on a system in equilibrium. So again, we need to refer to Lelia's principle and we're going to recall that equilibrium will reestablish itself based on any disturbances caused to maintain an equilibrium state. And so going back to our given reaction, we are told that we've got a negative entropy change. So because our entropy change is negative, this therefore corresponds to heat being a product. So we can say heat is a product. So with regard to temperature changes on this system, if we were to remove heat from the system, then recall that according to Lesley's principle, we would be removing a product in this case. And so equilibrium would reestablish itself by shifting in the direction to make more heat from removing that heat originally. And so equilibrium would shift to the right towards our product side. So we can note down that equilibrium shifts to side where heat is a product, or rather we should say where heat is present. So in this case, we've got heat as a product. So equilibrium would shift to the right. But if we were to add heat to our system, then according to Lelia's principle equilibrium will shift to the side where the reactants are. So we would say equilibrium shifts in the reverse direction. Whereas initially where we stated, if we remove heat equilibrium will shift to the side where heat is present. So in this case, heat is a product. So equilibrium shifts in the forward direction. So because phosphorus oxy chloride is a product along with heat. In given our negative entropy change, we would definitely want to decrease heat in order to increase our concentration of phosphorus oxy chloride. So going to our answer choices given, we would confirm that we would want to ultimately have a higher pressure and a lower temperature in order to favor the formation of more product being phosphorus oxy chloride at equilibrium. So we would rule out choice B because it states that we would need a higher pressure which is correct, but a higher temperature which is incorrect. We would also rule out choice C which states that we would have a lower pressure. No, we want to have a higher pressure since increasing pressure will favor the side with regard to equilibrium that has a lower number of moles of gas, which is our product side where phosphorus oxy chloride is present. And we can also rule out choice D because it incorrectly states we need a higher temperature. So that leaves us with choice. A as the only correct choice in our final answer, which correctly states the favorable conditions at equilibrium where we should have higher pressure and lower temperature to form more phosphorus oxy chloride. I hope that this made sense and let us know if you have any questions.

Is the yield of SO₃ at equilibrium favored by a higher or lower pressure? By a higher or lower temperature?
2 SO₂(g) + O₂ ⇌ 2 SO₃(g) ∆H = -47 kcal/mol

Key Concepts

Le Chatelier's Principle

Equilibrium Constant (K)

Exothermic Reactions

Watch next