Help for Boyles Law lab

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Help for Boyles Law lab

• Announcement
• You do NOT have to answer questions 4,5, and 6
  for this lab!

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Help for Boyles Law lab

• Boyles law says P1V1P2V2. For our lab, this
  means that the PV product should be the same for
  ALL five trials.
• In other words,
• P1V1P2V2P3V3P4V4P5V5
• where the subscript 1 refers to trial 1, 2
  refers to trial 2, and so on.

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Help for Boyles Law lab

• But were all PV products the same for all 5
  trials? Lets look at a sample data table.
• Compare this to your own Data Table 1 on page 97
  of the Boyles Law lab.

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Help for Boyles Law lab
PV products are NOT the same! Why?
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Help for Boyles Law lab
Review
Gas molecules in the syringe bop around and hit
the sides of the container, pushing against them.
The molecules are exerting a pressure.
As you decrease the volume, you have the same
number of molecules flying around, hitting each
other more often, and hitting the walls of their
container more often. Youve increased the
pressure inside the syringe.
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Help for Boyles Law lab

• Something you need to consider Is there really
  no pressure on the syringe system when no books
  are on top of it? If there is a pressure, what
  causes it?

Lets assume there is some other pressure that
weve forgotten about. If its a constant
pressure that weve forgotten, it will be the
same for all five trials. Well be able to plug
it into all of the pressures we measured and it
will make the PV product nearly the same for all
5 trials. Well call this extra pressure x and
try to solve for it by plugging it into the PV
product.
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Help for Boyles Law lab

• To make the math easy, well solve for x by
  plugging it into the data for two trialsand
  well just pick trials 1 and 2 (you could pick
  any or all trials).

P1V1 P2V2 (1 book x)(22.0mL) ( 2 books
x)(17.7mL) 22.0booksmL 22.0xmL 35.4booksmL
17.7xmL 4.3xmL 13.4booksmL x 3.1 books
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Help for Boyles Law lab
So lets add this extra pressure to all of our
readings and see if the PV product for all five
trials are reasonably close. If they are, this
means that there really IS a constant extra
pressure. Compare this next data table to your
own Data Table 2 on page 99 of the Boyles Law
lab.
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Help for Boyles Law lab
Sweet! The PV product is consistent for different
pressures and volumes. Boyles Law holds! There
is also a constant extra pressure we need to
consider.