Hey all - having trouble with this question:
At 92.2 C, the Kp for the following reaction is 0.2000 atm-1. If you were to place exactly 0.200 atm of N2O4 into a 1.00 L vessel, what would the partial pressure of NO2 be once equilibrium was established?
2NO2 --------> N2O4
A) 0.025 atm NO2
B) 0.200 atm NO2
C) 0.350 atm NO2
D) 0.400 atm NO2
I understand how to set up the equilibrium table, but like the solution says - using intuition would save time. How can you determine the change in NO2 partial pressure just from the Kp value given and the amount of product? Is there a general concept like if Kp is less than 1, the reaction favors the formation of reactants? Also how did BerkReviewTeach find out the N2O4 amounts for each choice? Thanks!!
At 92.2 C, the Kp for the following reaction is 0.2000 atm-1. If you were to place exactly 0.200 atm of N2O4 into a 1.00 L vessel, what would the partial pressure of NO2 be once equilibrium was established?
2NO2 --------> N2O4
A) 0.025 atm NO2
B) 0.200 atm NO2
C) 0.350 atm NO2
D) 0.400 atm NO2
I understand how to set up the equilibrium table, but like the solution says - using intuition would save time. How can you determine the change in NO2 partial pressure just from the Kp value given and the amount of product? Is there a general concept like if Kp is less than 1, the reaction favors the formation of reactants? Also how did BerkReviewTeach find out the N2O4 amounts for each choice? Thanks!!
BR General Chemistry Sample Question 3.9
Perhaps a distribution chart can help here. Let's consider the four answer choices.
· · · · · · · · NO2 · · · · N2O4
start · · · · · 0 · · · · 0.200
choice A · 0.025 · · · · 0.1875
choice B · 0.200 · · · · 0.1000
choice C · 0.350 · · · · 0.0250
choice D · 0.400 · · · · 0
Choice A can't be equilibrium, because there are more products than reactants. Given that K = 0.20, there must be more NO2 than N2O4.
Choice B can't be equilibrium, because plugging into the K expression yields 0.1/(0.2)exp2 = 0.1/0.04 = 10/4 > 0.200. Given that K = 0.20, that can't be right.
Choice D can't be equilibrium, because there must be at least some product.
Only choice C remains standing, thus it must be the best answer.
As the answer explanation states (BR page 174 of General Chemistry I), this question is designed to demonstrate that you don't really need to employ a great deal of math to solve numerical-based questions in a multiple-choice format.
BTW, if it makes you feel any better, the questions you sk are the usual suspects that most of our students ask about. Getting those questions correct is far less important to your preparation than figuring out a logical way to solve the questions quickly. You are doing quite well from what it seems. Three chapters down and seven to go.