GasesAn Exploration in Ideal Gas Behavior

Loosely adapted from: Philip Dutton University of Windsor, Canada and Martin Silberberg

Some Important Industrial Gases

Name (Formula) Origin and use

Methane (CH4) Natural deposits; domestic fuel

Ammonia (NH3) From N2 + H2 ; fertilizers, explosives

Chlorine (Cl2) Electrolysis of seawater; bleaching and disinfecting

Oxygen (O2) Liquified air; steelmaking

Ethylene (C2H4) High-temperature decomposition of natural gas; plastics

Helium He 4.0Neon Ne 20.2Argon Ar 39.9

Hydrogen H2 2.0

Nitrogen N2 28.0Nitrogen monoxide NO 30.0

Oxygen O2 32.0Hydrogen chloride HCl 36.5

Ozone O3 48.0

Ammonia NH3 17.0

Methane CH4 16.0

Substances That Are Gases under Normal ConditionsSubstance Formula MM(g/mol)

The Three States of Matter

Important Characteristics of Gases

1) Gases are highly compressible An external force compresses the gas sample and decreases its

volume; removing the external force allows the gas volume to increase.

2) Gases are thermally expandable When a gas sample is heated, its volume increases; when it is

cooled its volume decreases.

3) Gases have low viscosity Gases flow more easily than liquids or solids.

Important Characteristics of Gases

4) Most Gases have low densities Gas densities are on the order of grams per liter whereas

liquids and solids are grams per cubic cm, 1000 times greater.

5) Gases are infinitely miscibleGases mix in any proportion. An example of such is air, a mixture of many gases.

Properties of Gases: Gas Pressure

• Gas Pressure

• Liquid Pressure

P (Pa) =

Area (m2)

Force (N)

P = g ·h ·d

Pressure of the Atmosphere

• Called “atmospheric pressure,” or the force exerted upon us by the atmosphere above us.

A measure of the weight of the atmosphere pressing down upon us.

• Measured using a barometer - A device that can “weigh” the atmosphere above us.

Pressure = Force Area

A Mercury Barometer

Effect of Atmospheric Pressure on Objects at the Earth’s Surface

Construct a Barometer Using Water

dwater = 1.00 g/cm3 dHg = 13.6 g/cm3

Height of water column = Hw …of Hg column = HHg

HgW

Hg W

dH

H d Hg

W HgW

d

H Hd

HW = 10.3 m = 33.8 ft

W

gmL

gmL

13.6760 mmHg 10340 mm1.00

H

The Mystery of the Suction Pump

Because of the density of water, a “suction” pump can only pull water from a maximum depth of ~10 m (~34 feet) regardless of the quality of the vacuum or how fast the handle is pumped.

For wells deeper than 34 feet, the water must be pushed up from below.

Manometers

Common Units of Pressure

Unit Atmospheric Pressure Scientific Field

pascal (Pa); 1.01325 x 105 Pa SI unit; physics, kilopascal(kPa) 101.325 kPa chemistry

atmosphere (atm) 1 atm* Chemistry

millimeters of mercury 760 mmHg* Chemistry, medicine, ( mm Hg ) biology

torr 760 torr* Chemistry

pounds per square inch 14.7 lb/in2 Engineering ( psi or lb/in2 )

bar 1.01325 bar Meteorology, biology chemistry, physics

Converting Units of Pressure

Problem: A chemist collects a sample of carbon dioxide from the decomposition of limestone (CaCO3) in a closed end manometer, the height of the mercury is 341.6 mm Hg. Calculate the CO2 pressure intorr, atmospheres, and kilopascals.

Solution:

PCO2 (torr) = 341.6 mm Hg x = 341.6 torr 1 torr1 mm Hg

converting from mmHg to torr:

converting from torr to atm:

PCO2( atm) = 341.6 torr x = 0.4495 atm 1 atm760 torr

converting from atm to kPa:

PCO2(kPa) = 0.4495 atm x = 45.54 kPa101.325 kPa 1 atm

Characterization of a Gas Sample

To fully characterize any gas sample, 4 variables must be accounted for:

Pressure (P)Volume (V)

Quantity of gas in moles (n)Kelvin Temperature (T)

Experiment this week

Determine the relationship between:

P and VP and T

Vernier Pressure SensorNote: Pressure must not exceed 220 kPa. Start with

syringe at 10 mL and compress no further than 5 mL. Draw plunger back to get larger volumes.

Set up LoggerPro to collect data on command: Experiment | Data Collection

Change Mode: Events with Entry

A Note on Pressure Versus Temperature:What must be constant?Use a small Erlenmeyer flask and the plastic tubing to attach the sensor. Clamp the flask below the surface of water in a big beaker. Use ice for subambient temperatures. Heat to no hotter than about 80°C

Lots of little parts. Please don’t lose them. Use a 60 mL syringe rather than the 20 mL supplied in the box.

Attach syringe to Leur-lock with a gentle push……then a gentle twist. It doesn’t have to be really tight. Really, it doesn’t.

Other NotesThe thermometers don’t know how to swim!

– Please don’t teach them

This investigation, Author 2: Introduction and Conclusion3: Discussion1: Data/Results and Experimental

This investigation, AuthorB: Introduction, Conclusion, Data/ResultsA: Discussion and Experimental