2007-07-03 04:01:59 · 5 answers · asked by Anonymous in Science & Mathematics ➔ Chemistry
The laws of thermodynamics are summed up in the following equation:
P*V = T
Where P = Pressure, V = Volume, and T = Temperature.
For the can experiment, the thin walls of the can mean that pressure can remain constant for the purposes of the demostration. When P is held constant in the equation, you get:
c * V = T, or c = T/V
Which translates into a directly proportional relationship. That means that when T goes down, V must also go down. When you cool the can, the temperature drops, and since the volume must also drop, the can collapses.
For examples of the other relationships, consider a pressure cooker, where volume is held constant, and temperature rises, increasing the pressure, or a tire pump, where you press the handle down, decreasing the volume of air in the pump, but increasing the pressure (temperature remains constant).
2007-07-03 04:23:32 · answer #1 · answered by Bryan F 3 · 1⤊ 1⤋
Not a higher vacuum, but an easier one to do. Most labs don't have a good vacuum pump. It also will give the teacher an opportunity to show the gas laws and allow simple calculations by measuring the amount of water tht drips out of the can. Converting the grams to steam and knowing the volume it would make at 100 deg. C will give you a close hit on the vacuum produced when it condensed.
2007-07-03 19:43:36 · answer #2 · answered by Brian T 6 · 0⤊ 0⤋
Filling the can with steam drives out the air.
It the can is Immediately sealed, and the can allowed to cool, the steam condenses and, in so doing, the pressure inside the can decreases to a high vacuum.
The atmospheric pressure acting on the large surface area of the can causes it to collapse.
(It will also work using an inch or two of very hot water).
(Brian T, no one is talking of vacuum pumps but of the vacuum created when the steam in a steam filled vessel is condensed and its resultant HUGE decrease in volume).
(Condensing steam decreases in volume by about 1,700 times. i.e. 1,700 cc of steam will condense to 1 cc of water).
2007-07-03 11:51:38 · answer #3 · answered by Norrie 7 · 0⤊ 0⤋
The steam replaces part of the atmosphere in the open container. Cap the container and cool it; the steam goes to liquid water and the pressure inside goes down.
This is the basis of one of several variants of the collapsing can demo.
2007-07-03 11:06:57 · answer #4 · answered by ChemTeam 7 · 1⤊ 1⤋
Because it drives everything else out.
2007-07-03 11:09:21 · answer #5 · answered by ag_iitkgp 7 · 0⤊ 0⤋