The pressure of a gaseous sample is caused by what? What device is used to measu

Question

The pressure of a gaseous sample is caused by what? What device is used to measure gas pressure? Describe how it works. Atmospheric pressure is different than gas pressure. How so? A sample of gas occupies 5 liters at 100°C and has a pressure of 2.5 atm. What will the pressure of the gas be if the temperature stays at 100°C and the volume is reduced to 1 liter. Whose law applies to this problem? A balloon is filled with helium gas. How many grams of helium are required to inflate the balloon to a pressure of 1.2 atm if the volume of the balloon is 2 Liters at273 K. 1. 2. 3.

Explanation / Answer

1. The pressure of gas sample is governed by equation PV=nRT . This is ideal gas equation and according to it, any change in volume, temperature or number of moles cause change in pressure as R is gas constant. The device that is used to measure gas pressure is manometer. It measures the pressure exerted upon a column of liquid, it is called a manostat, or manometer. Atmospheric pressure is generally measured in millibars.

Atmospheric pressure is the pressure exerted by atmosphere on the surface as wellas object on the earth while gas pressure is the pressure that gas applies on the wall of container.

2. Boyle law applies here. P1V1= P2V2

5 L x 2.5 atm = 1 L X P2

P2=12.5 atm

3. Applying ideal gas equation PV=nRT, we get n=PV/RT

n= (1.2atm x 2 L)/(273K X 0.08314 atm L/mol-K)

n= 0.11 mol

now mass of He = mol X molecular wt

.11X4 g = 0.44g

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