Total Pressure Help

Test Preparation AP Sciences
1

<p>The gases are all placed in a container (12L) with constant Temp.</p>

<p>2.0L He at 2.0atm
1.0L O2 at 3.0atm
3.0L Kr at 1.0atm</p>

<p>So Dalton's Law of Partial Pressure states *for a mixture of gases in a container, the total pressure exerted is the sum of pressures that each gas would exert as if it were alone<a href="Verbatim%20from%20my%20textbook">/i</a></p>

<p>That is P(total)=P(He)+P(O2)+P(Kr)</p>

<p>Using PV=PV I find the pressure of each gas as though it was in the 12 liter container alone</p>

<p>2.0atm*2.0L/12L=.33</p>

<p>1.0L*3.0atm/12L=.25</p>

<p>3.0L*1.0atm/12L=.25</p>

<p>P(total)=.33+.25+.25=.83atm</p>

<p>Is this correct?</p>

<p>It is a MC question and the only answers are: </p>

<p>1.0atm, 2.0atm, 3.0atm, 4.0atm, 6.0atm. </p>

<p>Did I do it right or did I misinterpret the Law of Partial Pressures</p>

<p>My teacher did it like this SumV<em>SumP=P(total)</em>V(final)</p>

<p>SumV=2.0L + 1.0L + 3.0L=6.0L
SumP=2.0atm + 3.0atm+1.0atm=6.0atm</p>

<p>6.0L*6.0atm/12L=3.0atm</p>

<p>She's said that is right and I told her my way and she pretty much without much thought, said it was wrong. (she's one of the teachers that's never wrong)</p>

<p>So did I do it right or what? The book gave a similar example and I did it my way and got the same answer, her was way off. But if I say that, she'll just say the book is wrong.</p>

<p>If I am wrong, explain to me why, thanks.</p>

2

<p>You did it right.</p>

<p>Wow!
Your Chem teacher messed up big time.
There is no relationship like this:
SumV<em>SumP=P(total)</em>V(final)</p>

<p>Taken right from Zumdahl 6th ed p.207 example problem (meaning there is no error) to prove that there is no such relationship.</p>

<h2>46L He 25C 1atm + 12L O2 25C 1atm —> tank 25C P=?</h2>

<h2>- In the book, find mols first then use mols to find new pressure of each gas then add together. Solve using Boyle’s Law (your way) is good too.</h2>

<p>Ptotal = 11.7atm (go ahead and check)
Now let’s use your teacher’s equation.
SumV<em>SumP=P(total)</em>V(final)
58 * 2 = x * 12
9.7 atm = x which is NOT 11.7 atm</p>

<p>There is no such identity!</p>

<p>Just use an example problem in the book then prove her wrong. She could accuse the book wrong if she wants. Let she be proven wrong by the authors.</p>

<p>I feel bad for you, having to cope with such a teacher. Incompetent AND “no, I am always right.”</p>