TITLE: PV = nRT = BANG !
AUTHOR: DAVID J FRANKLIN, WEISER HIGH SCHOOL,
WEISER, IDAHO
GRADE LEVEL/SUBJECT: grades 11-12
Chemistry and Physics.
OVERVIEW: The ideal gas law is often difficult for
students to deal with. Manipulating the equation with
algebra can be confusing.
PURPOSE: This experiment will excite and focus the
students on this important prediction tool :
PV = nRT
OBJECTIVE(s): Students will be able to:
1. understand the ideal gas law and how it is used
as a prediction tool.
2. know the properties of 2 liter soda pop bottles.
3. explain the behavior of nitrogen (both liquid and
gas).
RESOURCES/MATERIALS:
Liquid nitrogen ( we get ours from the local vet),
thermos, 2 liter PET bottle with lid, garbage can,
water safety equipment.
ACTIVITIES AND PROCEDURES:
1. Place a large plastic garbage can (50 gal) at
least 30 yards away from buildings, cars, PEOPLE,
STUDENTS, etc.
2. Fill the garbage can at least 1/2 full of water.
3. Using a funnel, place about 100 ml of liquid N2 in
a 2 liter PET Coke Bottle. Teachers should do
this; wear safety equipment.
4. Cap the 2 liter bottle tightly and toss into water
filled garbage can. Run back toward students.
(You have 15-20 seconds prior to bottle failure.)
5. Enjoy the loud explosion of the bottle.
6. Now, analyze the situation using the ideal gas
law:
P1V = nRT1
P2V = nrT2
P1 = nR = P2
-- -- --
T1 V T2
100 ml N2 --> ________ moles N2
V = 2 liters
7. Convert units: atm --> psi, etc.
I have heard rumors that the PET bottles fail at
200 psi. See if you agree.
TYING IT ALL TOGETHER: This spectacular demonstration
opens the door for using the Ideal Gas Model: PV=nRT.
Similar cases can be considered quantitatively. Graphs
(P vs.T) can be considered. Other gases can be
considered.
Have fun !
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John Kurilecjmk@ofcn.org